The Trouble with “Road Tubeless”

It’s always interesting when bike industry people talk among each other, off-the-record. On the ride from the airport to Paul Camp a few weeks ago, one bike tester was still visibly shaken when he related: “My tubeless tire blew off the rim yesterday. I almost crashed.” Worried that this might have been one of our tires, I asked about the brand. He mentioned a big maker, known as a pioneer of  “Road Tubeless”. The tester continued: “I had it inflated to 90 psi, well under the max. I was just riding along, when suddenly – bam!”

Tubeless tires are becoming popular these days. Using inner tubes inside your tire almost seems like a throwback to the 1950s. Cars have not used inner tubes in over half a century, and mountain bikes have gone tubeless, too. Many of us have been riding our Allroad bikes, with their wide tires, tubeless for years.

Finally, road bikes, with narrower tires, are going tubeless, too. But it hasn’t always been smooth sailing: There are more and more reports of tires blowing off the rims. What is going on? Why are tires with inner tubes safe at high pressures, but the same tires sometimes blow off the rim when mounted tubeless?

An inner tube doesn’t just hold air, it also reinforces the joint between the tire and the rim. Air pressure pushes the tube against the tire so that it no longer can move independently. For the tire to blow off, a very small section of the tube must stretch tremendously, so the tire can climb over the rim’s edge. As flexible as inner tubes are, they get to a point where they don’t stretch any farther – pull on a tube, and you’ll notice this. That makes it very hard for the tire to blow off the rim.

Without an inner tube, there is nothing reinforcing that joint. If the fit between rim and tire is even just the slightest bit loose, the tire can slide upward, and – bam! In fact, even with a perfect fit, there is a point at which a tire blows off the rim: Tire beads can stretch a little, and the higher you inflate the tire, the more force there is stretching the bead. That appears to be the root cause of the problem: Road tires typically are run at relatively high pressures.

Thinking about this, I realized that “Road Tubeless” is a bit in uncharted waters: Usually, tubeless tires run at much lower pressures. Tires for cars and motorcycles are generally inflated to less than 45 psi. (The exception is airplane tires with up to 200 psi, but those are a very special design.)

All these tires also are much stiffer than bicycle tires, which helps them stay on the rim. A supple tire can move in just one small spot, which makes it much easier to climb over the rim’s edge. I was surprised at Paul Camp to hear about the tester’s experience with a tire that isn’t even known for its supple casing. But compared to car or motorcycle tires, even stiff bicycle tires are supple…

There have been a few isolated reports of our 700C x 35 mm Bon Jon Pass tires blowing off the rims, too. We’ve wondered whether perhaps there was a manufacturing error. We mounted one of the tires from that production run on a wheel with a Reynolds carbon rim that we had measured carefully to make sure its diameter was exactly to spec. We inflated the tire to its maximum pressure of 90 psi (6.2 bar) – without problems. The pressure has already gone down to 85 psi by the time I took the photo – there was no sealant in the tire for reasons that will become apparent in the next paragraph.

I then inflated the tire further. 100 psi was fine. 105 psi, no problem. A few more pump strokes, about 108 psi, and – bam! The tire blew off the rim. I was wearing ear protection, and there was no sealant inside the tire, so no damage was done.

Of course, few people would inflate a 35 mm tire to 108 psi (7.6 bar). Even with tubes, the Bon Jon Pass is rated to a maximum of 90 psi (6.2 bar). And as long as everything is perfect, you can run them tubeless at this pressure, too. But in the real world, not everything is perfect. The diameter of different rims can vary considerably. Panaracer’s engineers found that the rims on many production bikes are a bit smaller than spec, because that makes it easier to mount the tires on the assembly line. Of course, this also results in a looser fit of the tires.

This also explains why the few instances of Compass tires blowing off the rims have mostly been with Bon Jon Pass tires: They are our narrowest tubeless-compatible tire – 35 mm wide – and people tend to run them at higher pressures. On the other hand, the gravel racers love this tire and report zero problems despite the often brutal riding conditions. But they run their Bon Jons at 60 psi or less…

Over the last year, I’ve been testing every model of tubeless-compatible tire in the Compass program. I’ve mounted them without tubes on a range of bikes, both Bicycle Quarterly test bikes and my own machines. I’ve experienced zero problems, but I also run them at pressures of 60 psi (4 bar) or lower. I remounted the Bon Jon Pass that blew off the rim and inflated it to 60 psi, put in some sealant, and took it for a couple of rides. As expected, it was fine.

Based on this experience, we recommend: Do not exceed 60 psi (4 bar) when running Compass tires tubeless. If you need higher pressures, please use tubes. Since the problems with running tubeless tires at high pressures are not limited to Compass tires, I’d recommend this for all tubeless tires – and especially for high-performance tires that are relatively supple.

BJPASS_result-750x481

However, you also don’t want to run too low a pressure with tubeless tires. If the tire flexes excessively, this will break down the casing until it starts to leak (above). With a narrow tire, you have a narrow window between “too high” and “too low” pressures. On a 35 mm tire, 60 psi (4 bar) still is plenty for most riders. (I usually ride my Bon Jons at about 35-40 psi.) But if we were to offer a 26 mm-wide tubeless-compatible tire, 60 psi isn’t enough even for a light rider. Yet going higher than 60 psi would risk blowing the tire off some rims.

With wider tires, you don’t have that problem. I run the 54 mm-wide Rat Trap Pass tires on my Firefly at 40 psi (2.8 bar) on smooth roads. At such a “high” pressure (for tires this wide), the bike feels like a racing bike. On gravel, I can go down to 22 psi (1.5 bar) without risking damage to the casings. I run them tubeless now, after suffering two pinch flats during the Otaki 100 km Mountain Bike Race in Japan (above). As I found out, riding over really rough ground at very high speed will pinch-flat even 54 mm tires!

I feel that for riding on rough gravel, tubeless really is the way to go. Choose tires that are wide enough, run them at low pressure, and you shouldn’t have trouble. (Unless your rims are way out of spec.)

For road riding, the advantages of tubeless tires are less clear. Pinch flats are much less of an issue on the road, unless you still ride ultra-narrow tires. All the testing I’ve seen – including our own – indicates that the rolling resistance of tubeless tires is no lower, and perhaps even higher, than using thin, lightweight inner tubes. That isn’t surprising: You replace an ultra-supple inner tube with a liquid sloshing around inside your tire.

What about flats? One nice feature is that the sealant inside the tubeless tire automatically seals small punctures. But it appears you don’t have to go tubeless for that: Some riders use sealant inside their tubes. They report that it also seals small punctures in the tube – provided you use it from the start, when you mount a new tire. (With an old tire, during a puncture, the air may not escape through hole that is right above the puncture in the tube, but through a bigger hole from a previous puncture that is elsewhere in the tire. Then the sealant flows into the space between tire and tube, creating a mess without sealing the tube.)

Based on all of the above, we concluded that at this time, running high-pressure tires tubeless isn’t worth the risks. Can these issues be resolved? It’s difficult to say. Perhaps “Road Tubeless” is the way of the future, or perhaps it’ll be like radial tires for bicycles. Cars have used radials for decades, but for bicycles, they never caught on.

What needs to happen to make tubeless tires safe even at high pressures? Clearly, the interface between tire bead and rim must become more standardized, and manufacturing tolerances must become tighter. With a “perfect” rim, it’s already fine to run our 35 mm tires tubeless at 90 psi, but how do we get all rims to be perfect?

It might also help to increase the size of the interface between rim and tire bead. Modern cars have rim flanges that are 17.5 mm tall – three times as tall as most bicycle rims. However, that means a complete redesign of the tire/rim interface, with the result that the new tires would not be compatible with old rims, and vice versa.

The tire bead also might have to become less stretchy, but there are downsides to this. Tubeless-compatible tires already have stiffer beads than “standard” models. There aren’t any stiffer materials than what is being used, so making them even stiffer means adding weight and bulk. We haven’t given up hope yet: Together with Panaracer, who make our Compass tires, we continue to research tubeless technology in the continuing quest to improve our tires further.

For now, here is the take-home message for running tubeless tires:

  • For tubeless, we recommend a maximum pressure of 60 psi (4 bar).
  • If you are riding on gravel or rough stuff, tubeless eliminates pinch flats. And you’ll be running less than 60 psi anyhow.
  • If you ride on the road and need more than 60 psi, use inner tubes. Not just with Compass tires, but with other brands as well.
  • Even on smooth roads, Compass’ wide tires roll as fast as our narrow ones. Getting wider tires and running them at pressures below 60 psi is a good way to use tubeless on the road.
  • When mounting a tire tubeless, first inflate it 20% higher than the pressure you’ll be riding. Let it sit for a while to make sure it will not blow off your rim. Then decrease the pressure before you ride the bike. That way, you know that you aren’t at the upper pressure limit for that particular tire/rim combination.

Tubeless technology holds great promise, but like everything, it should be applied where it makes sense and where it is safe. In a future post, we’ll talk about tips on how to set up Compass tires tubeless.

Photo credits: Nicola Joly (exploded tire), Cyclocross Magazine (damaged casing), Toru Kanazaki (Otaki 100 km Race)

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
This entry was posted in Testing and Tech, Tires. Bookmark the permalink.

131 Responses to The Trouble with “Road Tubeless”

  1. RayM says:

    If you use sealant and let it cure, it will “glue” the tire to the rim. This should increase the pressure needed to blow the tire off the rim.

    • RayM says:

      I agree with Jan that there is a sweet spot. The question is how to find it for the combination of a rider, wheel, and tire.

      I’ve had a tire blow off the rim while it was inside the cab of my pickup truck. White juice spattered everywhere. The temperature was not especially hot. I had just loaded the bike into the truck and made it only a couple of miles from my house and then BANG!

      Now, after mounting and adding sealant to a tire for its first time, I shake the wheel then do a gentle, short ride (< 1 mile) to distribute the sealant I then let the wheel sit overnight before riding.

      "You never know what is enough unless you know what is more than enough." – William Blake

  2. larryatcycleitalia says:

    Intelligent advice, thanks. Sadly, too many are under the old “if some is good, more is better” spell and this includes tire pressure. I’ve watched cyclists pump the tires so hard that you can almost see daylight under their feet as they abuse that floor pump while its hose bulges from the strain! More than once I’ve rescued one from a tire right at the verge of blowing off the rim – despite having a tube inside. Keep singing the praises of wider tires at lower pressures!!!!

  3. Nicolas says:

    Great reading Jan ! totally converge with my own testing…and the risk of blasting your pant and my flashs cases is really too high to try it anymore !

  4. Vik says:

    One data point. I’ve run 32mm x 700c Compass tires at ~70-75psi tubeless on Velocity Blunt SL rims with no issues. When they wear out I’ll buy the 35mm version so I can run lower pressures. I can’t run larger tires in my bike with fenders.

  5. Frank Toman says:

    Hi Jan.
    Thanks for this post. It answers some questions … particularly about removing the valve core and adding sealant to my tubes.
    I had some blowout issues mounting Babyshoe pass tyres to Velocity blunt ss rims with inner tubes! Several times I would inflate them to about 50 psi (higher than I intended to run … but wanting to feel confident that I wasn’t on the upper limit) and 20 minutes later I’d hear the small explosion in the garage as it blew off the rim … destroying a fancy lightweight Schwalbe inner tube to boot.
    Gabe from ‘Compass Tech’ patiently worked it out … the high pressure rim tape I was using (Schwalbe) is apparently too thick. I haven’t had any issues since switching to the skinny tubeless rim tape. (When you are next in Tasmania Gabe I’ll buy you a beer!)
    Best. Frank

  6. Neil says:

    I was under the impression that tubeless road tires needed to use a different material for the bead, due to the higher pressures of inflation, and the tendency for beads to stretch as you highlight above. I thought I had heard Kevlar or carbon was the material of choice, because it doesn’t stretch. Any thoughts? Beyond the reprofiled bead shape, do Compass tires use something other than the standard material for the bead?

    • Compass tubeless-compatible tires use a different bead that stretches less. The exact material is proprietary, but it’s the strongest, least stretchy available today. That is why making the beads even stiffer would require adding more material and more bulk.

      • Fred Blasdel says:

        Several of your competitors produce tires with beads that don’t appreciably stretch at all, they mount exactly the same every time over the life of the tire. This isn’t new technology, some of these tires have been available for a decade.

        Even your latest “TLR” tires fit dramatically looser after being mounted once! You’re seriously losing customer trust every time you make a proudly blind statement like that.

      • Fred, not sure you’ve tried the recent Compass tubeless-compatible tires. The bead doesn’t stretch noticeably. In fact, the tire shown in the article blew off the rim, yet its bead returned to its original length, and the tire mounted fine afterward.

      • HaloTupolev says:

        >”Even your latest “TLR” tires fit dramatically looser after being mounted once!”

        Hasn’t been my experience. I’m not running them tubeless, but I’ve needed to use tire levers every time I’ve seated my Rat Trap Pass ELs, and they don’t seem to be getting any looser.

      • Fred Blasdel says:

        Jan I had a customer’s brand new SBH stretch noticeably just in April, I used thick tape to ensure a very tight fit yet it still blew off the rim, and wasn’t tight anymore when remounted (with a tube).

        Have you been making undisclosed running changes to the construction of the tires?

      • brand new SBH stretch noticeably just in April

        If a brand-new tire blew off the rim, it probably was an undersize rim, not a tire that stretched.

        Have you been making undisclosed running changes to the construction of the tires?

        We always strive to improve our products. If we told our customers about every little or big change we make to our products, they’d get bored pretty quickly!

  7. STS says:

    While there are without doubt problems with some combinations of tubeless road tires and rims and a dependable and accepted standard for Road Tubeless is clearly needed you generalize somethings that should not be generalized.
    Two things should be mandatory though.
    1. Only use tubeless tires for tubeless. Only those can be expected to have a bead material which is less stretchy than the Kevlar / Aramid stuff commonly used in folding clinchers.
    2. After installing a new tubeless tire always inflate it to 50% more pressure than the highest one you’ll ever use. Use ear and eye protection. Let it stand overnight in a place where it will do no harm if it comes off. When you come back on the next day inflate it again to that testing pressure. Wait some more minutes. If it passes this test it will not pop off even when the temperature in the tire raises during use due to brake heat or hot tarmac.

    There is already more than one test out there showing that the most advanced tubeless tires like the Schwalbe Pro ONE have a lower rolling resistance than comparable tube-type clinchers. But the most compelling reason for Road Tubeless is safety. People who run clinchers labeled as 25 mm wide (which are still the maximum on most road bikes) on rougher roads may still have pinch flats. Especially on chip seal where you’re typically not able to see smaller rocks or stones because of the structure of the road surface you might run over a stone and pinch flat your tube. If it happens in a turn that most often leads to a crash. I’ve seen this several times during the years when I ran a cycling trip company whose trips were mostly run on French roads where chip seal is still wide-spread. Some of those cases ended in a hospital, some even with broken bones.
    So for me riding tubeless tires on the road has become self-evident ever since they were available in 2005/2006. I never had one come off a rim and it also never happened to one of our customers of whom many converted to Road Tubeless over those years. Many of those guys used and still use the Hutchinson Fusion 2, Fusion 3 and Intensive tires which in reality measured only 23 mm. So they typically ride them with pressures above 100 psi some even with 120 psi.
    If tire and rim fit well together and if the tire bead is made from a longitudinally stiff bead core even those high pressures are not a problem.
    The test described above is your simplest way to find out if the combination you’re planning to use is safe and it takes the guess work out of it until a reliable standard – which is in the works – is firmly in place.

    • The tire that blew off for the tester was one of those you describe as “safe” above. Also, with respect to rolling resistance, the data I have seen does not indicate lower rolling resistance for tubeless tires.

      Steel drum tests only measure hysteretic losses, but those are them important ones here, and they show the Schwalbe Pro One tubeless version has higher hysteretic losses than the standard version with inner tubes. See http://www.bicyclerollingresistance.com/specials/schwalbe-one-tubeless-clincher (Note that the drum test does not measure the overall resistance of a tire, because it neglects the suspension losses. That is why these tests show all tires having lower resistance at higher pressures, something that has been disproven many times on the road.)

      • Rider X says:

        Jan. That link is for Schwalbe’s first generation of road tubeless, the One, not the newest generation Pro One – which is what the poster is referring to. (Yes, confusing naming distinction). It first generation was as responsive as riding a tire stuffed with wet sand. The second gen is much improved putting it on par with the clincher only + latex, with the added benefit of sealant to steal punctures.

      • Sorry about that. It’s hard to keep up with all the “new and improved” products companies put out. Glad the Schwalbe tires are improving. Has anybody seen independent testing of the latest version? Even on a steel drum – this is one place where the hysteretic losses alone are important…

      • STS says:

        Jan,

        did the tester you refer to also mention the rim he used? While being a cycling journo should make sure he used a rim designed and properly dimensioned for tubeless use my experience tells me that this is not so self-evident. People who want to try out this “tubeless thing” often venture into the unknown without given much thought about the requirements. If you include those people’s experiences into your database used to judge whether a system is safe or not, good working or not, your conclusion becomes flawed. What I based my comment on is not only my own personal experience but also that of some hundred customers, road cyclists, I talked into using tubeless over the years. I would not dare to contribute to your blog entries if I only had my personal and thus somewhat limited experiences. The internet is full of that kind of rather useless “information” which is nothing more than an opinion.

        I conclude that if done properly Road Tubeless is safe. Whether its advantages are worth the disadvantages remains a personal decision. But saying that it’s not safe is not correct. Ignoring the max. tire diameter or width on a car and installing tires that are too big because they seem to fit when you install them is also not safe. But it’s only a user error as much as using unsafe combinations of TL bicycle tires and rims.

        A couple of weeks ago Bike Radar published the results of a well-done test of the fastest road tires. The Schwalbe Pro ONE proved to be the fastest. While the test did not include one of your tires as far as I remember they had a lot of tires in there that should qualify as representing the current bicycle tire technology when it comes down to speed.

        I’m fully aware of the limitations of steel drum tests. In fact as far as I know I was the first journo who did real world rolling resistance tests with Powermeters on timed sections for German Mountain BIKE magazine back in 1999. But as you say for that kind of evaluation the drum test delivers some valuable results.

      • I appreciate your thoughts. I don’t know what rim the tester used, but it was probably whatever the test bike came with. If customers cannot trust that the bikes they buy are equipped with parts that work, then we have a problem…

        Regarding the Bike Radar test, I was surprised that this test still is done on steel drums, and still claims that higher pressures roll faster. The latter finding discredits the results, since we have shown time and again that this isn’t true on real roads. As a scientist, I am well aware of the temptation to accept flawed data as better than no data at all, but unfortunately, that isn’t the case.

        The Bike Radar guys tried to explain the tire pressure thing by saying on smooth roads, higher pressures are faster (even though their drum was textured to simulate rough roads), but we’ve shown that even on smooth roads, high pressures don’t roll faster. During the transition from the old thinking (narrow tires, high pressures are faster) to the new findings, we have this muddle of old and new ideas, with little rigorous examination of the methods.

      • Rider X says:

        Bicycle rolling resistance has an update test (I assume 2017 version of the Pro One will be similar):
        http://www.bicyclerollingresistance.com/road-bike-reviews/schwalbe-pro-one-tubeless-2016

        Bike Radar also has a fairly in-depth set of drum and roll-down tests of a variety of road tires including the Pro One:
        http://www.bikeradar.com/road/gear/article/best-performance-road-tires-lab-tested-49101/

        I realize you don’t want to muddy the waters (i.e., focus on hysteresis over suspension losses), but have you thought about submitting some compass tires to bicyclerollingresistance.com? Given the larger volume they will likely be ranked under touring tires, which I am sure they will lay waste to the stiff competition (sorry pun intended).

      • Thank you for the links to the drum test that shows even the latest Schwalbe to be faster with an inner tube than tubeless. Of course, without an inner tube, the tire may be more comfortable, reducing the suspension losses, which might make up for the disadvantage that the drum tests show.

        We considered submitting tires to http://www.bicyclerollingresistance.com, but it really doesn’t make sense to submit Compass tires to a discredited testing protocol that measures only hysteretic losses and still shows that that higher tire pressure reduces rolling resistance. We all know that in the real world, higher pressures don’t make tires roll faster, even on smooth roads.

        Our Compass tires are different from most other makers’ tires in that we don’t use steel drum testing when developing the tires. Our tires aren’t optimized for steel drums, but for the best performance and comfort on real roads.

      • greg says:

        Had used tubes for many many years on the road and of course that came with that many flats ,almost 10,000 k later using road tubeless not a single flat or issue using 3 different brands of wheels.
        Change comes hard for a lot of people .
        Use the right rims ,tires and pressures you just may find yourselves delighted with the results .

      • Frank says:

        The same site lists the Schwalbe Pro One as having ca. 8% less resistance than the earlier One.

    • charles elfot says:

      I like tubeless technology, and I ride a tubeless MTB–and have done so since the DIY days when few tubeless-ready tires or rims were available for that purpose. I offer that last comment to respond to your statement that “Only use tubeless tires for tubeless”. Were it not for a generation of DIY riders, tubeless would have caught on much more slowly than it did in MTB. Your statement better suits road riding, with typical modern road wheels and tires, for which there is less of a margin for error, due to the higher pressures as Jan points out .

      I do think that tubeless will ultimately prevail in cycling, but your advocacy is still somewhat premature, as you note in your final paragraph. Your belief is informed by your experiences, but as Jan points out, there is much contrary data. As tires have recently improved in performance there may finally be a reason for beginning to consider tubeless road riding as a good alternative to the tube system.

      The foremost reason probably is not safety. Tubed tires are not unsafe. That you can specify instances where a tubeless system might be superior to tubes is not broad proof of concept.

  8. Charlie Johnson says:

    Jan
    Thanks for a thoughtful, well written piece on a complex subject.

  9. Jim says:

    On my road bike I’m running Schwalbe Pro 1 tubeless 700×25 tires at 70f / 75r on Stan’s Alpha 340 rims. So far I’m very satisfied with the tires, no problems mounting and seating them. The ride is very plush. The actual measurement on the tires is almost 28mm and the recommended pressure listed on the sidewall is 70-110psi although I don’t think I’d go over 80-85. My weight is 150.

    • There are many people who have great experiences with tubeless tires at higher pressures. But even if just 1% of the tires blow off the rims, that is too high a risk in our estimation. If it works for you, don’t change it…

      • Pete says:

        Jan, If only 1% is too high, then why don’t you remove the “Tubeless Compatible” labelling from your tires. Surely if you don’t see an advantage (in TL) and you feel that the risks are high it would me an ethical thing to do?

        As you are fully aware, I had two blow offs on two rims which have both carried Schwalbe TL tyres without issues. Rims are ETRTO spec sizing. So I saw a 66% failure rate at 90psi (not riding pressure, but for mounting/verification purposes).

        I appreciate this post as I can see that your accepting some responsibility for the design issue, however would appreciate it if you update the advertising material and the printed maximum pressure on the tire sidewall.

      • Peter, you are one of the handful of customers who’ve blown a Compass tire off the rim. Since we have close relationships to our customers and shops, we do hear about pretty much every issue with our tires. Of course, we don’t know how many customers run our tires tubeless and how many run high pressures, but the 1% failure rate is as good as we can get.

        In your case, the Axis rims on your bike are known to be undersize. (We had one other customer report the same problem with those rims.) We are glad that the much stiffer Schwalbe tires work on your rims, but making our Compass tires equally stiff would defeat the purpose of the supple tires we love and ride. Unfortunately, your rims seem ill-suited to running supple high-performance tubeless. The rim probably are fine for use with high-performance tires and tubes.

        Our web site clearly states the recommended pressure limit for tubeless. Removing the “tubeless compatible” designation would really be a disservice to the hundreds of gravel riders who have been enjoying these tires tubeless. As long as you run reasonable pressures, these tires are perfectly safe to use tubeless.

      • Peter says:

        Jan, regarding your comment on the Axis 4.0 Wheel set. I spoke at length with Specialized regarding your statement of them being under sized. They have been manufactured to be compliant with the ETRTO specification for size and Specialized’s Engineering Team disagree with your statement. I would also like to note that every other tyre fitted to either of the two wheel sets involved have required tyre levers, except the Compass Branded tyres.

      • The ETRTO specification is for mounting the tires with tubes, not tubeless. That shows that the answer you got from Specialized is simply skirting the issue you are experiencing, rather than providing useful information. If they told you that they had tested these rims tubeless with a large number of tires from various manufacturers, that would be more useful – but companies who don’t make their own stuff often prefer to let the customers do the testing.

        Whatever it is, several customers have had trouble mounting Compass tires tubeless on the Axis rims. Specialized’s rims are all over the map – on my Diverge, the carbon Bontrager rims are so tight that mounting tires requires tire levers and brute force. Every time, I am concerned that I’ll break the carbon of the rim, because I have to push so hard on the tire levers. And this is on a 30 mm-wide rim – usually, wider rims make tire mounting easier because there is more room for a deeper well in the center.

        These are typical problems of a mass producer who is farming out production to the least expensive bidders without adequate oversight. Of course, the company will disagree with any statement that their product may be sub-optimal. Until somebody gets badly hurt, and there is a recall…

    • STS says:

      Jim,
      with that very rim you want to do the safety test (inflate tires to 150% of your riding pressure) with every new tire you install. The Alpha 340 is proven to have to small of a diameter. If a tire is out of tolerance it might blow off. Play it safe!

      • Jim says:

        When the Pro Ones were first mounted on the Alpha 340 rims I let them sit overnight, without sealant, at 98psi. By morning they were down to 94 and still on the rim. I emailed Stan’s today and asked for max pressure for that rim and they replied that the rim would handle the max pressure listed on the tire. I also checked their site for 340 specs and found a max of 116psi with a 23mm tire and down to 45psi for a 32mm tire. So I feel reasonably confident that running the 25mm Pro Ones, actual 27+, at 70/75 should be safe. Thanks for the help.

      • Fred Blasdel says:

        Stan’s Alpha rims are many things, but they are absolutely not undersized! The entire purpose of their ‘BST’ standard is to be significantly larger in diameter than the ERTRO spec allows.

      • STS says:

        Fred,
        not sure how you come to that conclusion with regards to the Alpha 340 but the problems with that rim with regards to tire “rentention” are well documented at least here in Germany. Back in those years when that rim was new there were some severe accidents because of tires coming off that rim. Most of those tires were tube-type clinchers, but a considerable percentage were tubeless. In some cases those tires were new and installed by professional mechanics (even mechanics of a tire company) shortly before they blew off.
        NoTubes did a “voluntary” replacement of the early version of that rim because it was also too light and developped cracks at the spoke holes very quickly. But I never saw them advising against using that rim with tube-type clinchers which was clearly dangerous. In Germany their distributors eventually published that advice after the biggest European cycing magazine had reported about the accidents and their own tests showing that that rim is not safe.
        In the meantime NoTubes might have (or not) changed the diameter of that rim – I honestly don’t know – which is an easy thing to do but the main reason for that problem was not the diameter at the bead shelf but the outer diameter of the horn. And you can’t change that without changing the extrusion.

    • Peter says:

      The ETRTO specification is to enable correct fitment of tyres to rims. 700c rim’s bead seat should measure 1954mm circumference. For the Axis 4.0 wheel to be ‘undersized’ as you put it then this figure should measure up smaller, correct?

      With two layers of Stans rim tape (my wheels), this measurement, confirmed by measuring three times with a metal tape, is 1956mm. My guess is without the rim tape it would be exactly as per the ETRTO spec, as per Specialised’s statement. Also the distance between the bead hook and the seat is 4mm, which coincidently is the same size as the bead on a Schwalbe 35mm TL tyre. The BJP is 2mm.

      Comparing the bead circumference between the Schwalbe 35mm and the BJP 35mm it is clear that the BJP is several millimetres larger. (compared by inserting a identical tubes to both tyres, inflating to 4psi to enable the BJP to hold shape and laying one tyre over the other and lining up the beads at 90°, 180° and 270°, then comparing the variation at 0°).

      So from this I can conclude that the Axis 4.0 is not ‘Undersized’ as you claim, and that it is in fact the correct size as stated by Specialized. I can also conclude that the BJP tyres (at least the examples I currently hold), are in fact larger than they should be for a 700c wheel, and that with a bead half the size of the distance between the bead seat and the bead hook, coupled with the larger circumference of this bead that this would enable the bead to move around within the bead area of the rim. The bead would want to sit at the outer regions near the bead hook, but not be locked into a position due to the small size of this bead. The end result is a dangerous fitment either tubed or tubeless. Maybe with a tube the pressure and resistance of an inner tube may stabilise this movement, but given all of the other tubed tyres I have all have a 4mm bead, I wonder whether a 2mm bead is truly a good idea.

      If I may quote you:

      “companies who don’t make their own stuff often prefer to let the customers do the testing”

      “Of course, the company will disagree with any statement that their product may be sub-optimal. Until somebody gets badly hurt, and there is a recall…”

      Something to ponder, Compass Cycles should reflect on your commentary regarding Specialised and look within…

      You have stated that 1% is an acceptable failure rate of your tyres. This means tyre failure on one in every 50 bicycles fitted is what you consider to be an acceptable.

      • The ETRTO specification […] 700c rim’s bead seat should measure 1954mm circumference.

        It’s not quite so simple. The ETRTO measurement for the bead-seat diameter is 621.55 mm +/- 0.5 mm. However, that measurement assumes a thick rim tape, so add a millimeter on each side of the rim, and you get between 623.05 and 624.05 mm, or a circumference of 1957.4 to 1960.5 mm. And remember, the ETRTO standard is designed for inner tubes, and for a mass production setting, so a slightly looser fit of the tires is not only OK, but desirable to make tire mounting easier. For tubeless, you’d want the fit to be tighter, especially since you use a much thinner rim tape. So assuming your measurement of 1956 mm is correct, it does appear that your rims are slightly undersize.

        Beyond that, there is more to rim design than just bead-seat diameter: hook height, hook shape, etc. If it was simple, the ISO already would have established a standard for tubeless bicycle tires. They’ve been working on this for years – this shows that there is a lot to it. All we know that several Compass customers have had trouble with the Axis rims you use. Unfortunately, you are one of them.

        As to your measurements of the tire diameter, unfortunately, I doubt you are getting accurate measurements that way. Compass tires aren’t oversize – there is no need to make them that way. Our tires aren’t sold as OEM, so ease of installation in an assembly line setting isn’t a concern.

        You have stated that 1% is an acceptable failure rate of your tyres. This means tyre failure on one in every 50 bicycles fitted is what you consider to be an acceptable.

        I am sorry there is a misunderstanding. Please re-read… I stated that a 1% failure rate is not acceptable. This was in the context of riders who have had great experiences running our and other makers’ tires tubeless tires. I wrote that even if dozens of riders report problem-free riding, this isn’t enough, because even a 1% failure rate would be unacceptable. In fact, that is the reason for this blog post…

  10. Geoff Wendt says:

    As you know, I had a gen II JBP tire pop off after having used it for over 1,000 miles successfully. The only thing I did differently on that day was I added more stans sealant. I pumped them up to 60psi while cold and then went for a ride. I struggled at 14mph for 12 miles in a nasty headwind and then turned around and could easily hit 25mph+ on the flats. I weight 225 lbs. What are the odds that the heat from the speed and my larger weight contributed to the tire blowing off? Are any of your testing crew Clydesdales?

  11. greg says:

    Just read your article on tubeless tires .
    Right away I am wondering how it is possible to run a 23c Schwalbe Pro One Tubeless tire at a max of 60lbs with my 170lb weight ????
    I have used these tires for almost two yrs now without fail .
    I inflate my rear tire to 90psi ,my front to 85psi.
    They ride beautifully and feel quite fast on my road bike .
    They have never blown off a rim .
    My experience with these tires has overall been excellent.
    Would Schwalbe not be over run with lawsuits and why then is this issue of tires blowing off rims not announced by this manufacturer and the system removed from production ???
    When mounted on a proper tubeless rim then set up at 90psi or so these tires will never blow off a rim .
    Inexperience and the wrong rim then it is possible .
    Am upset that you have put the fear of god into a perfectly safe system and setting a great system back on its heels with this article .
    Greg

    • I am glad those tires work so well for you. You are absolutely right – with the “right” rim, tubeless tires can be inflated to higher pressures – not just Schwalbe tires, but our Compass tubeless-compatible models, too. Witness that in our test, the tire stayed on the rim up to 108 psi.

      Unfortunately, for the customer, it is almost impossible to determine whether they have the “right” rim or one that is slightly out of spec. The blowout that led me to write this post – the one the tester I met at Paul Camp experienced – was with another big brand of tires. That company is known for their expertise on tubeless technology.

      At Compass, we caution riders even if there is only a 1% risk of failure. As a small maker, we have the advantage of more direct communications with our customers, so reports of failures reach us much quicker than they would at a large manufacturer. And without a bureaucracy moving slowly to make decisions, we can also react more quickly. I wouldn’t be surprised if similar warnings came from other makers in the future. That doesn’t mean that you should stop using something that has been working well for you.

    • Zekker says:

      I ride pro ones 700×25, I’ve been testing for the right pressure and I found 75psi perfect for me, I race criteriums and the grip and rolling resistance at 75psi it’s amazing, I tested at 85psi and I stopped mid ride to deflate the tyres. This article main objective it’s to damage the reputation of a very good, fast and reliable tyre the market can offer

      • I can assure you that the goal of this article is not to damage the reputation of any tire – including our own Compass tires. The vast majority of Compass users who’ve been running our tires tubeless – even at high pressures – have had zero issues. But even a very small number of issues is too great a risk for us.

    • RickH says:

      Tire and rim combination is critical. Schwalbe and Shimano collaborated on bead/rim profiling for safety. Mavic have been trying to garner a standard rim design and width for the relative sizes of tires for industry worldwide. Wide tires on a too narrow rim will have the body of the tire roll the bead over its edge. Too wide a rim for a given tire size will cause a weakness between the tires bead hook and the rims bead hook.
      I have tried a Schwalbe Pro One with a recommended Shimano rim and had no problems fitting and inflating. I used the Schwalbe sealant but I ran the tires at a low pressure of ~60psi-75psi and damaged the casing. Unfortunately one bead was glued so hard to the rim, pliers and a lot of swearing didn’t remove it. I immediately thought of how this would work out on a long brevet away from anywhere.
      In use though they are terrific as long as you pay attention to the first sentence.

  12. BYcycles says:

    In general, “road tubeless” has always seemed like a big hassle for not much benefit. I suppose if the “road” is gravel or is particularly rough they might be worth it but on reasonably smooth asphalt, it’s hard to see the appeal. In my typical road riding, I get maybe one flat a year and that’s usually due to me running over some puncture-inducing debris. I’ll take that over futzing around with sealant, special rim tape, etc. and worrying about the tire blowing off the rim.

    • charles elfot says:

      I agree completely. When there is no longer a need for sealant or fiddling with special rim strips, and performance is equal or superior to tubed road tires (wasn’t that the original justification?), I will begin to convert.

    • RickH says:

      My experience too.

    • verbekeerik says:

      When road tubeless was introduced by other brands, Schwalbe had a document on it’s website about why road-tubeless was pointless. (Now it is obviously not to be found anymore). They followed the crowd, but that doesn’t mean their reasoning was flawed. Just like you I haven’t had a pinch flat for years now.
      I hope non tubeless ready tyres will remain readily available so we don’t have to fight the bead everytime we change tyres.

      • Conrad says:

        I agree. I see more mechanicals with tubeless setups. In goathead country, maybe. Otherwise I don’t see the point of tubeless and I hate that it is affecting the availability of normal rims and tires.

  13. If you glue your tires on you will experience a delightful ride which is safe.

    • You mean tubulars? Agreed, if you have the time to glue them. It’s for good reason all the pros ride tubulars, and not “Road Tubeless”.

      However, with wide tires, the advantages of tubulars disappear. Some mountain bike pros used to race hand-made tubulars because this prevented pinch flats, but with tubeless technology (and far less than 60 psi), there no longer is much of a need for ultra-wide tubulars. Even so, I’m always tempted to get FMB make us a set of 650B x 48 mm tubulars!

      • jonowee says:

        Mountain bikers run tubulars for one of the same reasons as road pros, not really for puncture prevention. By gluing the tyre and tube onto the rim you can ride farther on a flat before reaching the pits or service vehicle while deflated clinchers would struggle to keep on the rim.

  14. Sebastién Poule says:

    Tubeless rim design has probably not reached its acme. I was amazed by this fellow’s observations on rim wall deflection (in a static situation) as a function of tire size and pressure. If you include heat, road shock, lateral forces and breaking forces, maintaining a reliable tire-rim seal becomes a mind blowing challenge. http://www.killasgarage.bike/uncategorized/tire-width-and-rim-stress-a-video-demonstration/

  15. John.J says:

    So how does ones establish the “real” tire pressure ?

    Over three trials, using my 1980’s Silca floor pump with its built-in gauge, I raised my Compass 700C x 32 Stampede Pass tire to 80psi. Then I compared that reading to both my Accu-Gage PR160BX and my SKS Airchecker. The results are Silca 80psi, Accu-Gage 72-73psi and SKS 65-67psi.

    Knowing how some countries measure horsepower, it doesn’t surprise me that the Silca reads highest. Accu-Gage claims “mechanical accuracy rating is ± 2% from 30% to 60% of scale” (ghmeiser.com/about.htm). The SKS gauge readings are a little surprising.

    For now I am going use the Accu-Gage for tires.

    – John

    • I have found similar issues. In the end, I just stick with the same gauge, and I use the pressure that I have found to work best through experimentation. Whether that really is 38 psi or actually 42 psi doesn’t really matter, as long as it works and I can replicate it.

  16. RayM says:

    Jan: I’d love to see more data.
    Would you please repeat the experiment using the same tire, wheel, and pump.
    Will the second, third, and successive bangs continue to occur around 108 psi or is the tire degraded?

    • The wheel went back to the maker, but we can use a different wheel. However, I am not sure what we gain by establishing whether a tire deteriorates if it blows off the rim multiple times. I hope no user will blow off their tires multiple times. I recommend that if you blow off a tire once, you either reduce the pressure quite significantly or install tubes.

      • RayM says:

        I would like to know if a tire, once blown off, could be used tubeless at lower pressure, if it should be relegated to duty with tube, or if retired and not used at all.

      • The answer in cases like this is always “It depends.” The tire that blew off my rim was undamaged, and has been fine since. But I cannot guarantee that all tires that blow off rims will be fine to use. Inspect the tire and use good judgment. When in doubt, don’t use it – a new tire is much less expensive than a visit to the hospital emergency room!

  17. Nicolas says:

    Not long ago, I was ridina a tubeless 28mm tire that blew off my rim. I had previously ridden these tires during hundreds of kilometers of mountain roads, and they were feeling rock solid.
    What I did differently was just inflated my tire with a friend’s pump… By chance, the blowout happened at almost 0 kilometers/h while clipping in, but for me this safety margin is really too thin to be ridden anymore.

  18. hobbanero says:

    Leonard Zinn has some good data on the dramatic increase in force on the tire sidewalls that happens as you increase inflation pressures. You are starting to compress the rim itself at high pressures, and particularly with an aluminum rim, you will increase your chances of a blowout. I have had a blowout on a Stan’s Iron Cross (which, to be fair, has a 40psi max rating) at 45 psi, but no problem with the same tire at 70psi on an Enve carbon rim, which is much stiffer. HED recommends dropping the pressure by about 10% on their (wider than typical) rims for this same reason. Even with a tube, the increased force because of the larger air volume will compress the rim, effectively reducing spoke tension and reducing the life of the wheel. Not to mention poor ride quality.

  19. David Lewis says:

    You make one point that I have never understood. We always lower the pressure when riding gravel to improve traction. Yet the sharp loads that would break the cords in the sidewall are much more likely to occur on gravel. You have established that higher pressures on pavement do not reduce rolling resistance due to suspension losses. So I do not understand why we do not establish a minimum pressure that will prevent cord damage on gravel and just use that. Why raise pressure above that level when we return to pavement?

    • Minimum pressure depends on rider weight. That is why we don’t specify one. A 100 lb. rider can (and should) use much lower pressures than a 250 lb. rider. As to why not use the lowest pressure that doesn’t cause casing damage on the road: At pressures that low, the tire will collapse during hard cornering. You need higher pressures to corner safely. In the end, tire pressure isn’t just a set of numbers: Every rider needs to figure out what works for them, based on their weight, their riding style and their preferences.

  20. BrendanM says:

    Last season I ran Schwalbe S-Ones on my Stan’s Grail rims. Even with all the usual tricks it was tough to get them on, but that was confidence inspiring, and the beads popped in effortlessly after that. This year I’m trying out BJPs on the same rims. The tires fit on the rims too easily for my liking, and getting them to seat (even with my air compressor) was quite a challenge. I resorted to adding sealant first, and blew one off the rim (not sure on the exact PSI, but pretty sure it was between 60 and 90). I’ve been riding them at 40-50 psi, and love the suppleness, but I don’t have the confidence in them I would like. In particular, if I push hard on the sidewall at these pressures, I can see just a bit of air and sealant escaping. I’d really like to keep these set up tubeless in order to run lower pressures when on gravel, but I don’t want to be thinking about a tire coming off the rim on a fast descent either.

  21. Peter says:

    I feel that there are certain bicycle tyre companies who have the technology worked out for successful TL solutions and there are others who want a slice of the sales pie. I have had tyres from both.

    I feel that this article is a great step forward for Compass Cycle in coming to terms with the need for a slice of the TL pie. I hope that this will result in a change of direction for Compass, to stick with what they are good at.

    For me, I have done thousands of KM on road tubeless tyres and have seen the advantages. I for one will be sticking with TL, as it is a safer solution when done right.

    • It’s clear that many riders have had good experiences running tubeless tires, whether Compass or others. We certainly have had almost zero issues with wider tires that are run at lower pressures. With higher pressures, it seems to be the bike testers, who ride many bikes and many tires over a short period of time, who find the issues. It’s only a small fraction of rim/tire combinations (and these depend no only on the model, but also on the manufacturing tolerances of the individual rims) that are affected.

  22. DM says:

    I’ve been running babyshoe pass tires tubeless on Stan’s Valor wheels for 500 miles so far, but I run them at about 40 psi. Singletrack, gravel, road, they do it all. They mounted very easily, didn’t leak sealant like I experienced with mtb tires and they ride like a dream. It’s been said before, but I think rim-tire combination needs to be right for things to work.

  23. John says:

    I have the non-tubeless version of the Bon Jon Pass 35mm. I run with tubes at 50psi F and 60psi R. I weight 200lbs. I want my next tires to be the same but the tubeless versions. I didn’t read all 56 comments above mine. Just wanted to know if there’s some kind of guide for how much “less” pressure to use when switching from tubes.

  24. This is a very interesting discussion. Jobst seems to indicate that tires (tubular and clincher) get tighter as inflation pressure increases: http://yarchive.net/bike/inflation_constriction_force.html because the bias ply makes the “hose” of the tire shorten in length. Since this effect would seem to prevent tires blowing off rims at high pressure, what other effect is present that overwhelms this beneficial force? Perhaps the rim widening mentioned above? Any other effects that can be measured/tested?

    • I think that the casing, even of a stiff budget tire, is not rigid enough for this effect to be important. The tire doesn’t have to expand uniformly to blow off the rim. I suspect that the most important factor is how much the bead stretches, with a secondary (probably very minor) factor the reduction in diameter of the rim due to the air pressure. Everything else is relatively floppy… A theoretician like the late Jobst Brandt might conclude that higher spoke tension might pre-load the rim more, so it constricts less under the same air pressure, but I doubt that this has an effect in the real world. Otherwise, aluminum rims would have more problems with tires blowing off than carbon…

      • Chris Richards says:

        I’m not a wheel builder, but I thought I read claims of significantly reduced spoke tension caused by tighter/stiffer tubeless beads on a wheelbuilding forum the other day. It made me curious if anyone like Shimano or Fulcrum are increasing spoke tension to compensate for the potential for tubeless use. Could it then follow that a high-tensioned tubeless-ready wheel system might ride more harshly when used with tubes and looser, traditional beaded tires? Just curious.

      • Fred Blasdel says:

        Spoke tension normally drops at least 20% when you mount a tire on a lightweight tubeless-ready rim, whether you use a tube or not. The tire would have to be extremely loose for it not to constrict the bead shelf of the rim once seated.

        Spoke tension does not affect ride feel, unless it’s so low that the wheel is ready to collapse

  25. morlamweb says:

    Yet another reason for me to keep uses inner tubes. The high cost of tubeless hardware, and the high risk of a tubeless tire popping off the rim, tells me that the technology is nowhere near ready. It’s just another excuse to try to get me, and other cyclists, to buy into the new thing.

    • Fortunately, you can use inner tubes with the new technology. Even if you have “tubeless-compatible” rims and tires, there is nothing that prevents you from using inner tubes. I know I’ll continue to use tubes on test bikes that need more than 60 psi in tire pressure.

      • morlamweb says:

        Yes, that’s true. The Rat Trap Passes are tubeless-compatible and I run them with tubes. When I next need new wheels – I wore out my last set a couple of years ago, after many years of use – who knows, tubeless might be the default option for clincher rims by that point. Were that the case, I’d still run them with tubes; I’m just not convinced that tubeless is a true upgrade over tubes.

  26. Eric Hancock says:

    This is really interesting.

    I’d enjoy hearing about the relationship to rim internal width and tubeless safety.

    I’m only riding Hed+ rims now, which have an internal width of ~21mm. With 28c tires on the road, I’d probably inflate them in the 60-65psi range with tubes. This seems close to your suggested “safe” range.

  27. schmidjo says:

    “. For the tire to blow off, a very small section of the tube must stretch tremendously, so the tire can climb over the rim’s edge. As flexible as inner tubes are, they get to a point where they don’t stretch any farther – pull on a tube, and you’ll notice this.”
    Well I would say Inner Tubes are flexible all the way to their bursting point. But yes, you are correct; an inner tube is pre-loading the tire bead against the rim. The late Jobst did a test cutting the tire bead (multiple places). It stayed on, pushed by the tube/pressure into the hook. With tubeless, the pressurized air is on all sides of the bead up to the sealing point; thus the forces on are (unfortunately) more balanced. Thus need to rely more on bead radial stiffness (high modulus materials are desirable). You are also relying on that mechanical joint of bead on hook, so it depends on their design also. Even with tubes, if the hook or bead are poor enough the tire will still blow off. .

    • What about hookless rims though? Only acceptable for low pressure MTB tires? http://www.bikeradar.com/us/mtb/gear/article/trail-tech-off-the-hook-40749/

      • When I read that article, I had doubts. How would removing the hooks reduce the likelihood of blowoffs and improve impact safety. If they said that it was the same, I might believe it. But removing material rarely makes something stronger in impacts. (Stress risers are another issue, and removing them can make a product last longer in fatigue tests, rather than impact tests.)

      • STS says:

        Jan,
        this bike radar article is about carbon rims. A hookless horn on a carbon rim is much stronger. On most carbon rims the hook is created by machining which translates into cutting fibers. That vastly reduces the impact strength of the structure. But even on rims where the hook is molded – which is anything but easy to do – that hook is always the achilles tendon of that rim.
        The bike company I work for as an engineering consultant did a lot of real world destructive testing of carbon rims before we committed to offering them as an option. The strength of a hookless carbon horn turned out to be absolutely amazing. When we were not able to destroy the rims in use we went into the lab. The impact strength – measured in Joule – necessary to crack a hookless horn turned out to be five times higher than what was necessary to deform the hooked horn of an aluminum rim used in mountain bike downhill racing.
        So manufacturing a hookless carbon rim doesn’t mean taking material away. In fact it rather means leaving material where it’s supposed to be in order to create a stronger structure. Adding a hook to that structure also increases the leverage of the forces acting onto the horn during an impact and thus exerting a bending momentum onto the horm where there is only a compressing force on a hookless horn.

      • Thank you for explaining this. It makes sense if you have an existing mold and your rim proves to be not strong enough. You take a 3 mm hookless horn and you machine of a 1 mm undercut for the hook. So you have 2 mm left. If you don’t machine it, you have a 3 mm horn. So if you underdimensioned your horn, then this is a band-aid solution to make it stronger.

        But if you start from scratch, designing a new rim, you would just factor in the material you will remove: make the hookless horn 4 mm, machine off 1 mm, and you end up with a 3 mm horn, too, but with the interlocking hook for the tire bead.

        As to the impact strength – if you bottom out so hard that you break the rim, you’ll also cut a high-performance tire. Downhill mountain bike tires have special reinforced casings to survive this at least sometimes, but that is also the reason why nobody rides them on flat or uphill courses.

      • loursblanc says:

        To me, the article appears to bring some interesting insight I never thought of: 1) Hooks try to define fit on the outer hook perimeter. 2) Hookless rims on the inner perimeter.

        I imagine, burping and blow-offs probably require most of the tire bead to move towards the center channel, as the bead (Kevlar, Aramid, Zylon or similar) cannot stretch sufficiently to release the tire (at least I would believe so, as tire mounting for example gains the required additional length by moving most the bead towards the center channel, and not by stretching it). This appears to happen more easily in the first situation. When tire seating is defined on the inner perimeter and in addition aided by a bead lock, I would think it is more difficult to free (through lateral impact) and move enough length of tire towards the center channel.

        Wouldn’t that explain higher resistance to blowouts?

        This certainly still needs tightly specified tolerances.

      • All rims (classic and tubeless) should support the bead on the inner diameter. There were some poorly designed rims in the past (Velocity Synergy, old-style Grand Bois): Their wells were too deep, and the tire had to float above the rim. This made tire mounting difficult, and it risked the tire coming off the rim when it deflated due to a puncture.

        When the tire blows off, it’s not that the bead moves toward the center channel. The air pressure prevents this. It’s really the bead stretching until it can go over the horn of the rim. With a stiff tire, you have to stretch it more, because the tire has a greater tendency to remain round. With a supple tire, it’s easier to deform the tire in just one place, where the bead then can go over the horn of the rim.

  28. Doug L. says:

    Thought about TL for awhile and after reading these comments I think I will wait to see if the technology progresses in a few months. All very good dialog and I agree with Jan for the type of riding I do these days commuting and packed gravel/paved trails with the grand kids. What I would like to see is rims/ spokes such that by adding the valve stem one could install the tire inflate it and be off no slime and no tape. Just take your felt tip applicator with sealant run it around the tire bead before tire installation/inflation and that is it. Keep the comments coming.

    • greg says:

      Campy and Fulcrum have rims without spoke hole such as the Campy Eurus and Shamal fantastic wheels on all accounts ,superb for 25c or less tubeless tires . No rim tape req,d 🙂

      • Doug L. says:

        Post script to mine of 30 May. I ride 32 and 38 mm tires on 700C 22-23 mm wide rims and am not a ware of rims this size without spoke holes. Do let me know if such an animal exists.

  29. Josh Deetz says:

    These issues are so often clouded by biased manufacturers, public relations and worst sloppy or non-existent standards. ISO,ETRTO,CIS,USTRO,JIS standards are grotesquely insifficient. First, let me address the points raised in this post. Innertubes are critical because they act as a source of pressure but also have friction on the surface between tire, tube and rim or rim strip. Blow-offs are more likely with tubeless than with Intertubes, but only when sizing is not controlled. Bicycle industry loves to talk about freedom of innovation and apparent need for no constraints. But this is rubbish, as we have constraints with tire sizes, a 700C can’t be swapped out with a 650B. So we need some boundaries, but how many?
    At present rims have a relatively narrow range of forms and sizes to conform to standards, but these rims are meant to be fitted with tires. Tires, on the other hand, have NO BEAD DIAMETER SPEFICICATION. This might seem crazy but standards published are driven by tire makers and therefore they remove constraints related to bead diameter and even bead stiffness (tensile modulus), So when someone at Panasonic (of any other tire maker) says things like “rim makers make rims smaller to make fitting easier” a grain of salt comes to mind. Rims come in slightly large slightly small and just right, no such tendency for small exists in the >50,000 rims I have measured. To be clear tire makers are not breaking any rules, they simply live in a wild west of free reign and lawlessness.
    When speaking of better tolerances, this too is a misunderstanding. For any given model of tire you will find a very narrow range of diameters when measured with a very sophisticated tool. While this model might be consistent, you might find the same apparent specifications from the same maker will measure a bit different. Take a ETRTO 622 specification from a single maker. Take two very different models, let’s say a trekking tire and a narrow road tire. Measure the two of these and they will differ, at times a shocking amount. Now tire centric logic says a tire bead should be tuned to ensure this width and casing construction is suitable for use, but let’s remember these all end up on one specification of 622 rim. So variations specific to this model mean variations from a target rim size. So tires even within a brand see variations that effect fittment.
    Now in the world of rims we have manufacturing tolerances which are narrow, usually +/-0.5mm, so again it’s not a tolerance issue as much as a designed profile problem. If a bead shelf is used, or it is has a 3.8mm~10mm hook height. Does it have a hump to lock the bead in place or not? Design plays a much larger role in fit variation than does manufacturing tolerances. I started in wheels and tires in the very late 70’s, while I didn’t find clarity in this issue until the mid 1980’s. Since then I’ve been pushing an improved standard to tire and rim companies alike, with pockets of success but not yet wide-ranging adoption. While 10’s of millions of rims per year are built to my standard, 100’s of millions more do not, and only a few tires conform. Four decades in, I remain driven, focused and confident the market will speak soon and a proper standard will be demanded by users worldwide.

    • The biggest problem for tire makers is that their tires are used with a huge variety of rim models. If we were to make one rim for each tire model, and allowed using only that one, I am sure we could design something that would work just fine.

    • STS says:

      “To be clear tire makers are not breaking any rules, they simply live in a wild west of free reign and lawlessness.”
      Thanks Josh. That’s exactly what it is.
      Having meetings with a group of product managers of a big bike tire company and listening to them how each PM defends his decision to go for a different ITC circumference for the tires he’s responsable for whereas his colleagues use different approaches for “their” tires leaves me always scratching my head in disbelief.
      During one of those meetings recently I learned that ISO is now involved to define a standard for road tubeless design. And there is hope amongst the guys at the head of product development that this soon to be released standard will be respected much better than any attempts by the ETRTO made to date.
      Do you have any further insight into this that you would like to share?

      • We’ve been discussing the proposed ISO standards with the Panaracer engineers. We also met a senior engineer from Araya who refuses to make tubeless-compatible rims until the ISO standard is established.

      • Conrad says:

        Huge props to Araya! That is the common sense approach.

      • It goes both ways. If intrepid riders hadn’t pioneered tubeless tires on mountain bikes, they’d still be getting pinch flats! But for an OEM manufacturer like Araya, it makes sense to wait until thing have shaken out.

      • STS says:

        I tend to disagree. If it were not for Hutchinson and Shimano (later joined by Campagnolo / Fulcrum) who pioneered Road Tubeless and introduced a system that worked safely right from the beginning and even with pressures up to 120 psi if you were so inclined, there would probably still be no Road Tubeless tire system. Because NoTubes only started offering rims for road tubeless use after Hutchinson already had produced those tires in the market for a while. And NoTubes deliberately chose to deviate from the Road Tubeless standard with their rim design. And that’s when the problems began. I’m still wondering why Hutchinson let NoTubes sell their tires as bundles although their rims where not really compatible. You might of course have a different opinion about the ride quality of those Hutchinson Road Tubeless tires when compared to ultra flexible tube-type clinchers or open tubulars but the vast majority of riders who tried out the Road Tubeless system (wheel and tire) never went back to a tube-type system. In fact I remember only one of our customers in all those years who chose to go back after he had a puncture on his first ride and the cut was so long that the sealant couldn’t seal it. He went nuts afterwards but we are still friends ;-).

      • Fred Blasdel says:

        I’m astonished to hear that Araya still exists! They haven’t had anything in the American market for decades.

      • Jim says:

        STS, You stated that Stan’s deviated from the Road Tubeless standard. In what way? As I mentioned above I have a set of older Alpha 340 rims that I’m currently running with Schwalbe Pro One 25mm tires at 70/75. So far no problems. When I originally bought the wheels I used Hutchinson tires tubeless at much higher pressures with no problems although I didn’t like the ride quality of the Hutchinsons. I used the wheels tubeless for one season and then went back to tubes and different wheels until this year when I decided to try the Pro Ones which I like very much. I emailed Stan’s yesterday after reading this thread and told them I had an older set of Alpha 340 rims and without mentioning any specific tire asked the max pressure for the rim. Their reply; “It can handle the max pressure listed on your tire”. On their website page for the 340 rim it states that max pressure with a 23mm tire is 116psi and with a 32mm tire 45psi. Unfortunately you can’t have it both ways. I have 35mm tires that have a max pressure rating of 70psi. So for me the major problem of tubeless is getting reliable information that I can trust.

      • STS says:

        Jim,
        please see what I wrote today in response to Fred who argued that the Alpha 340 is not undersized. I don’t want to double post. As I originally advised you should increase the tire pressure to 150% of your max. riding pressure for testing purposes. If the tires don’t blow off you’re fine. If the rim can’t handle that it’s better not to use it anyway for the sake of your safety. The Alpha 340 is a really light rim and NoTubes did not use any higher strength alloy for it but just Al6061 which is an alloy that has been in use for rims for ages. Modern light weight rims which are typically still a little heavier than the Alpha 340 despite a similar cross-section are often made from higher strength alloys like Al6069, to name just one, which has significantly more strength than Al6061. That goes to show that NoTubes really went to the limit (and possibly above) when designing the Alpha 340. As a rim for disc brakes which do not reduce the wall thickness of the rim’s brake track over time it might be o.K. for lighter riders but for heavier riders or those that want to use higher pressures I would disadvise from using it.
        After some 1,000 miles on a rim brake bike the side walls of the Alpha 340 tend to bow outwards under the pressure of the tire because they are already very thin when new. This phenomenon further increases the likelihood that the tires will pop off.

      • Jim says:

        STS, Thank you for the info. I inspected my 340s this morning and found 2 small cracks around the drive side spoke holes so that will be retired immediately. The front wheel looks good and the rim measures almost 20.5mm across the brake track which is .5mm more than Stan’s specs so it’s possible that the track is bowing outward in which case it’s time to look at a replacement wheelset.

      • STS says:

        You’re welcome, Jim. I’m glad that I could help.

  30. Galen says:

    Two things about tubeless safety.
    First, tire blowoff pressure is partially dependent on tire width. A 60psi limit, generically, for any tubeless setup and tire size, is misplaced. Wider tires have higher casing tension (aka hoop stress) at a given pressure, which is pulling the bead off the rim. All else being equal, a wider tire will have a lower blowoff pressure than a narrow one.
    Second, a 1.2x safety factor is insufficient in an application like this. If the blowoff pressure on a given 700x35mm tire is really 108 on a listed rating of 90, that’s a problem. Between gauge error, user error, and reasonable misuse, a better listed pressure limit is in that 55-60psi range for a 2x safety factor.

    • You are absolutely right that the safe tire pressure depends on many factors. Tire width is only one of them. You have rim width, rim design, rim diameter, and temperature that softens the rubber. And many others. But as manufacturers, we have to provide guidance that customers can follow. Hence we recommend a maximum of 60 psi. Others aren’t so cautious, but the fact that their tires blow off the rims worries me – even if it happens only very occasionally.

      A 2x safety factor often was quoted in the past for tire pressure, but the reality is more complex. If you wanted to make cycling components with such huge margins of safety, the bikes would be so heavy and bulky that you wouldn’t want to ride them. I forget what the ISO standard requires for a safety factor for tire blow-off, but it’s much less than 200% of the maximum listed pressure.

      • Galen says:

        2x is not huge. You do not typically design non-redundant safety critical components to be within 20% of failure in regular use… especially when the normal error in use is 10% or more. The appropriate safety factor depends on failure mode, failure consequences, and other things, so you expect different components to have different factors. I don’t expect there are many components on a bike that are as low as 1.2x, or that a tire should be designed any lower than maybe 1.5x. If it is, that’s an unsafe design choice.
        And again, 60psi for your 35mm tire sounds smart, recommending it across all brands and sizes is not, b/c it’s disconnected from the physics of the tire’s size, even though it sounds conservative given the range of constructions. The listed 55psi limit in your 2.3″ may be really close to blow-off pressure, and 60psi in a 25mm road tire might be a recipe for tire damage and be under blow-off by 3-4x.

      • All our tires are tested by Panaracer and by us to ensure safety. The maximum pressure ratings are chosen to accommodate the fact that users will have different rims, different gauges (which may underread significantly) and different riding conditions. There is a significant margin of safety, and the reason we recommend 60 psi for tubeless is to ensure that a sufficient margin of safety is maintained.

        If you feel the need to set your own standards, it’s easy: Just inflate your tires to any value you choose, and you’ll see whether they’ll stay on the rim. It’s one of the few products where you can actually check the margin of safety yourself.

  31. daveqb says:

    Hi Jan,

    Interesting article. While reading I kept thinking “was tester’s rim a tubeless compatible rim?”
    I have read many times that although you can physically setup tubeless on any rim, it is strongly recommended to only run tubeless on rims that are specifically designed for tubeless. The issue is, I have been told, is using a non-tubeless rim for a tubeless setup you run the risk of blowing the tyre off the rim.

    One of your comments said you didn’t know if the tester’s rim was a tubeless rim. This would be the first consideration before considering running tubeless. I have read this so much I thought this was common knowledge now. Is it not?

    Also, one of the other advantages of tubeless that was missing in your article, I think, is in the event of a puncture the tyre is much less likely to roll off the rim compared to a clincher setup.

    Thank you.

    • While reading I kept thinking “was tester’s rim a tubeless compatible rim?”

      Of course it was a tubeless-compatible rim. These testers are not hobbyists, they are testing bikes from the big manufacturers, set up by the makers themselves. I can’t help but think that if the manufacturers’ mechanics can’t get it right, the average customer will have trouble, too.

      As to the tire staying on the rim in a puncture, that works with all tubeless-compatible rims, regardless of whether you mount the tire tubeless or not. The tire bead rests on a shelf, and unless you push it off manually, it doesn’t go into the well. (That is also why many riders have trouble when mounting or removing a tire from a tubeless-compatible rim for the first time.) When the tire is flat with no air pressure, it makes little difference whether there is a tube inside or not.

  32. Ray Ogilvie says:

    Can we use a better term than “non-tubeless” ? Wouldn’t “tubed” be more accurate?

  33. Mike Anderson says:

    Someone here described the tyre/rim standard in the bike industry as ‘lawless’, which it certainly is. In fact, in my 30 years in this industry I have seen a great number of failures due not only to poor design and sufficient peer review, but also due to the inherent difficulty of creating a product that is compatible across the range of those by other companies. The result to consumers and small businesses engaged in this affair is frankly, embarrassing.

    It is because of this ‘lawlessnes’ and general ignorance by your average industry expert on the limitations of products that are purportedly cross-compatible, that I urge you, Jan, to NOT fall victim to the tendency to follow the hype attached to the current tubeless trend. I’ve seen plenty of small, innovative, and well-meaning and highly intelligent people in this business run out of town due to litigation.

    It isn’t worth it.
    Listen to the wise voices at Panaracer. Your tires, nor anyone else’s, will be compatible as a tubeless tire with every rim on the market until a standard is well established and enforced. Until then, you are at great risk of litigation for suggesting anything to the contrary.

    Lastly, I’ve played with tubeless systems on mtbs, cross bikes and road bikes for years with a good number of failures along the way (using myself as the test pilot). The only tubeless systems that have never failed are the ones devised jointly by Shimano, Mavic and Hutchinson to ensure proper mating of the tire and the rim. All of the others rely on the weak logic of faith—or as they say here in New Zealand: ‘Don’t worry, she’ll be right, mate.’ This is not good enough.

    Keep up the good work. The industry needs more honest and sensible people like you. Just don’t be a victim of your own success.

  34. Albrecht says:

    I think the blow-off problem is caused by manufacturing tolerances. Even with tubes the problem occurs from time to time. I had Schwalbe Marathons which were very difficult to mount on the rim and Marathons which blew off unless mounted very carefully on the same rim. So the upcoming ISO standard will have to specify narrow tolerances and manufacturers will have to produce accordingly. Needless to say that this will lead to an increase of costs and prices.

  35. Bruce Dance says:

    I think I may have something to contribute to this discussion: A tubeless tyre can actually seal anywhere, i.e. from where the lip touches the base of the rim to where the hook edge touches the tyre. Car and motorcycle tyres are meant to seal at the lip; when they don’t, they tend to lose pressure in hard use because the bead is (transiently) pulled away from the rim enough for the air to come out. Apart from that it doesn’t seem to matter exactly where the seal is made; the bead is a tight fit on the rim and doesn’t (to any great degree) rely on air pressure and friction for tyre retention.

    Bicycle tyres are different to that. If the tyre seals at the lip, the loads on it are not very different from those seen when there is a tube fitted; the entire bead sees the air pressure and will generate a useful friction component that tends to help retain the tyre (which is IMHO a far more significant thing than the tensile strength of a typically flimsy tube).. But if the seal is made near the hook/bead edge instead, air pressure isn’t loading the bead in the same way and there is not the same friction force available. In this situation the tyre will tend to blow off the rim if

    a) the bead is flexible enough to stretch and sees enough load (the tension load in the bead varies pro-rata with tyre width and air pressure more or less) and/or

    b) the bead is a loose enough fit (under the service loads) that it can climb off the rim and/or

    c) the tyre ends up even remotely off-centre on the rim; this generates a highly unstable condition which can soon run away with itself and cause the tyre to pop off.

    Note that if the seal is made vs different parts of the bead at different points around the tyre circumference, the tyre might as well be off centre; it will see a very different loading condition at different places which is exactly the kind of thing that will blow the tyre off the rim.

    Also NB sealants may work as lubricants at times, soapy water etc may have been used to mount the tyre and there are known issues with residual oil etc on new rims and residual mould release compound on new tyres anyway. Between all these things there is plenty of scope for the tyre bead to (as well as seeing different loadings) also see highly variable friction coefficient which will again affect how likely the tyre is to stay put. [Years ago I had a new tyre blow off a rim, after it had been ridden on for about fifty miles; I happened to be looking at the bike at the time and I saw the tyre move on the rim in a c) type event. Once I’d cleaned the mould release compound off the tyre, and refitted it, it was OK…..]

    Obviously there is a problem at present with a lack of a decent standard; one hopes that this will soon be rectified. At present not every rim and tyre combination works at all well. However until tubeless tyres are designed in such a way as they may only seal at the lip itself, it seems likely that the available forces to retain the tyre are going to be ‘somewhat variable’ and that this alone may be enough to cause blowouts. In the meantime tubed tyres are far more tolerant, fit-wise, so I shall be sticking with tubes. In fact I already avoid rims that are designed with tubeless in mind, because ordinary tyres are often an unnecessarily tight fit on them.

    • But if the seal is made near the hook/bead edge instead, air pressure isn’t loading the bead in the same way and there is not the same friction force available. In this situation the tyre will tend to blow off the rim

      That is an interesting thought: that the beads may be standing on the rim well, without air pressure forcing them outward. Fortunately, it’s easy to see that in reality, this isn’t a problem: Air pressure always pushes the bead outward and toward the rim. Otherwise, the tire wouldn’t seat in the first place. During the initial seating of the tire, the only thing that moves the beads out of the well in the rim center is air pressure, and it continues to act that way as long as the tire is inflated.

      • Brucey says:

        whilst seating the tyre isn’t easy unless the tyre lip is dragging in (and hopefully sealing against) the bottom of the rim, a) tyres frequently don’t seat that easily and b) unfortunately I do not share your optimism that this will always remain the case once the tyre has much pressure in it.
        I have seen some tyres that seat and fit very well, so that they don’t really need any sealant. These tyres are probably not going to blow off the rim, either. But I’ve seen others where they don’t seal easily and others that move enough (eg because of bead stretch) when inflated that the tyre lip isn’t necessarily where the seal is made any more. In these instances it is pot luck where the seal is really made and therefore which part of the bead sees any beneficial (tyre-retaining) net air pressure load.
        Remember that there is always an appreciable load between the tyre and the rim edge; if this happens to make a **better** seal than the tyre lip (which it might do with increased pressure, say….), I think that air pressure can work its way behind the bead (even if the seal at the lip appears to be more or less OK) and that if this happens, this is one thing that helps the tyre to come off.
        It would perhaps be interesting to manufacture a set of test rims which have various deliberately introduced leak paths at different positions near the tyre bead, so that the actual seal location can be controlled and varied. If it can be shown that tyres are variously better or worse retained as a consequence (on rims of the same dimensions otherwise) then this would demonstrate the extent of this effect.

      • In your scenario, where the air pressure doesn’t push the tire against the rim wall, the tire bead would be free to move toward the center of the rim until it falls into the well there. I have never heard of this happening as long as there has been any air pressure in the tire.

        If a tire doesn’t seal, it’s due to pinholes at the rim/tire bead interface. The tire pressure always pushes the tire bead against the rim. In fact, that is how a tire is seated in the first place. You have plenty of air leaking, but you put in air faster than it goes out. Tire pressure increases, and that pushes the beads outward until the tire seats.

  36. Count me among the camp that thinks if a bunch of people are talking “off the record”, writing about it on your blog is a violation of that trust.

    • As a journalist, I am keenly aware of what is appropriate to do with things that people share with me. In this case, I won’t name the tester, nor the tire that blew off. If the tester had specifically asked not to relate this anywhere, it would be a different matter. So technically, this wasn’t “off-the-record”, but I would ask permission before naming names.

      And then we also have to weigh whether there is a compelling public interest to publish information. It’s been interesting to see all the bike industry people who’ve weighed in on the lack of standards. It appears this is a widespread problem, and they are happy that somebody finally is bringing it to people’s attention. It’s not something the marketing departments really want to talk about!

  37. Bruce Dance says:

    PS. I didn’t emphasise this point fully before, but if a tubeless tyre seals at the edge of the rim, rather than at the edge (lip) of the tyre in the rim well, there is essentially no tyre pressure load on the bead, forcing it into the hook part of the rim. In this condition, you may as well not have a hook bead profile at all, for all the good it is doing you. If this condition is ever likely to arise, the tyre bead will have to be a tight fit on the rim and much stronger/stiffer than normal in order to withstand the forces it sees.

    There is a parallel here; in the early part of the twentieth century so called ‘clincher’ tyres were popular for a while. These arguably only existed at all because Dunlop, realising that their tyres could not otherwise be patented, bought out the patent for wire bead tyres, and wouldn’t let others make to that design. Anyway the clincher tyres had a moulded lip at the edge of the tyre and little or no wire beading reinforcement. Presumably the bias angle of the plies was also set to help the tyres stay on, but the main tyre retention was achieved by the tube pushing the tyre lip into a very hooked section of the rim profile. Such tyres were used on bicycles, motorcycles, and cars. Weirdly these tyres tended not to stay on the rim if they were not inflated hard enough! Typical pressures were (at least) 60psi and they would last maybe 1000 to 2000 miles on a car or motorbike. You can still buy them for vintage vehicles (just) and despite their rarity they have (by blowing off the rim at low pressures it seems) claimed the life of at least one vintage motorcycle enthusiast within the last five years.

    Modern bicycle tyres rely partly on having stiff/tight beads and partly on having hooked rim edges so that the tyre pressure can provide some ‘clincher’ effect. History shows us that

    a) rims without hook beads don’t retain lightweight tubed cycle tyres very well and
    b) despite that that the ‘clincher effect’ isn’t enough by itself and
    c) that most modern tyres really need both to be secure

    IMHO Tubeless setups that seal in unpredictable ways can lose whatever benefit is obtained through the clincher/hook bead effect and until that issue is resolved, a lot of tubeless setups won’t be 100% reliable.

  38. Jon Blum says:

    Perhaps there is some lack of clarity about “off the record.” Usually that means “not for publication” (although it is typically assumed by the source that such information will still be used in some manner), but perhaps you meant something a little more complex. I speak to journalists occasionally, and assume they may report anything I say, unless I ask them specifically not to do so. Your position as both an industry insider and a journalist may create a situation that leads to people saying things they might not say to a typical journalist. As long as you respect the wishes of your sources, that is OK. Journalists who violate this understanding tend to find that their sources dry up, so in the long term it is not in their own interest to do so. Thanks for this informative report.

    • Journalists who violate this understanding tend to find that their sources dry up

      Exactly. For me, knowing the background is very important and useful if your goal is seeing the big picture. I’ve been working in the industry for more than two decades now, and I am glad people now tell me things that they might not tell others.

  39. John.J says:

    Has anyone actually measured their rims to determine if they within the appropriate specs ?

    Using the ease of which the tires mount hardly seems to be correct method for determining rim specification compliance.

    – John

    • Measuring the bead seat diameter of rims isn’t easy, and it requires removing the spokes. So it’s not something we can just do on test bikes…

      I’ve been thinking of a gauge that would be a “go/no-go” to determine whether a bead seat is too small or not. That gauge would look a lot like a tire bead. If it fits loosely, the bead seat of the rim is too small. If it doesn’t go on at all, the bead seat is too large. If it slides on just right, then everything is within spec.

      • STS says:

        It’s not that complicated, I think. And it’s actually good to measure it on the built wheel with the spokes under full tension. Instead of a ruler which exists for that task we use a long inner shift (or brake) cable. Lay it around the bead seat, pull it tight at both ends and ideally have a helper put a mark with a sharpy at one point where it overlaps. Afterwards when you put that cable into a vise exactly where one of the two marks is you can measure the ITC circumference of that rim. Divide that measurement and deduct twice the diameter of the cable and you have the diameter at the bead seat.

      • John.J says:

        I would think that a pi tape gauge would be able to give one a reference surface diameter that could be used to measure from for all the other surface dimensions needed to establish the “quality” of any rim.

        http://www.pitape.com/products-outsidediameter.htm

        – John

  40. Brucey says:

    I have made a tool to measure rims with. I mostly use it to measure rims prior to wheelbuilding, but it can be used to measure BSD and overall diameter even on built wheels.

    It simply comprises a marked-up aluminium channel extrusion (about 2m long) in which the wheel/rim is rolled so that the external circumference can be measured. +/- 1mm here gives a diameter measurement accuracy of ~+/- 0.3mm.

    The depth to the spoke seat (or the tyre bead seat) can be measured using a depth micrometer to ~+/- 0.1mm which gives an overall diameter measurement accuracy of ~+/- 0.5mm, which is good enough to sort the wheat from the chaff as it were, both for spoke length and tyre fitment purposes.

    You will note that (in contrast to many other methods) this method gives pretty accurate/meaningful readings even if the wheel/rim isn’t quite round. I got cheesed off with rims measuring differently in different places because they were egg-shaped, hence I built this tool.

    • John.J says:

      What were the results of measuring various rims before and after wheel building ?

      How did you decide what the appropriate measurement tolerance was ?

      What variation did you see across different examples of the same rim model and size ?

      Thanks !

      – John

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