Bicycle Quarterly: Performance of Tires

Perhaps the most influential topic in Bicycle Quarterly has been our research on the resistance of tires, first published in Vol 5, No. 1 (above). It is not a coincidence that 5 years after that issue was published, professional racers are adopting wider tires and lower pressures. How did all this come about?

My research started after I read a big test of racing tires in the German magazine TOUR in late 2005 (below). As part of their testing, TOUR measured the rolling resistance on a steel drum in a lab setting. They found that the “fastest” tires had half the resistance as the slowest. In real-life terms during a ten-kilometer time trial, the slowest tire (Continental Grand Prix 3000) would take 34 seconds longer than the fastest (a hand-made clincher with a cotton casing). TOUR noted this but did not critically evaluate the relevance of their results: 34 seconds in a short time trial is the difference between winning and 20th place.

Most of us don’t spend much time at “time trial” speeds, where wind resistance predominates, so I did a quick calculation to see what this meant for real-world riders. I found that the differences were even more significant. Furthermore, TOUR tested only high-end racing tires. What about the wider tires most of us used? Were we giving up significant speed? We had to find out!

The first thing to check was whether we could replicate TOUR’s results on real roads. We thought of a variety of tests, and concluded that a rolldown test had the most promise. Mark Vande Kamp suggested an old soapbox derby track that was perfect: It started steep and then gradually changed to a very gentle slope.

The first step was to get two sets of tires that TOUR had tested: The Deda Tre Giro d’Italia were the fastest in the test, and the Continental Ultra Gatorskins were among the slower tires. On a calm morning, we headed to the soapbox track. Each of us had mounted one of the sets of tires on our bikes. I rolled down the slope while Mark timed me. Then we switched wheels, so I could roll down with the second set of tires, on the same bike. We repeated this several times, and the results were clear: The Deda tires were significantly faster than the Continentals, just as TOUR had predicted.

The next step was to gather all the tires we wanted to test. It was a long list, and we eventually pared it down to 18 tire models. (We later tested additional tires.) To make the testing session more time efficient, we borrowed as many wheels as we could find, so we did not have to mount tires between tests. Then we waited for a perfectly calm day. In Seattle, this usually happens when the weather changes. During sunny days, the wind blows from the north, whereas it switches to the south on rainy days. In between, there are hours of perfect calm. From riding many randonneur brevets, we also knew that around sunrise, there was the greatest chance of no wind. Finally, a day came with a promising weather forecast. Long before dawn, we loaded up two Burley trailers stacked high with wheels, a floor pump, clipboards and everything else we needed.

Then we started our testing. Mark rode up the hill. He held onto a stepladder on the start line, so he would smoothly roll down the hill without wobbling or having to clip into the pedals. He used the same position during each roll-down: hands on the hoods, elbows locked. (We later confirmed in the wind tunnel that this position can be maintained with great consistency.) Two timekeepers recorded Mark’s time in the lower section of the run. We ran each tire/pressure combination three times to see how consistent our data was. We also ran the same tires on different wheels to check whether the wheels influenced the results. (They did not.)

We tested and tested all morning. Different tires, the same tires in different widths, the same tires at different pressures. Clinchers, tubulars, racing tires, touring tires, new tires and well-worn tires with thin tread.

We tested the same baseline tire three times during our test session – first, in the middle and last – to see whether conditions had changed. We were lucky: the morning was completely calm. It also was overcast, so temperatures did not change. (We later found that temperature greatly affects the rolling resistance of tires.) One morning was not enough to complete our testing, so we spent many more days on the test track. Sometimes we went out at 4:30 a.m. only to have a light wind spring up. All we could do was go home and hope for better luck next time.

At the end, we had pages and pages of measurements that we formatted for analysis. During our analysis, we found some interesting results:

  • The speed differences between our tires were even greater than those tested by TOUR. The fastest tire, the Deda Tre, rolled 20% faster than the slowest, the Rivendell Nifty-Swifty. A 20% difference in on-the-road speed is huge!
  • Wider tires roll faster. A Michelin Pro2 Race in 25 mm width was faster than the same tire’s 23 mm version, which in turn was faster than the 20 mm version.
  • Very high tire pressures don’t roll much faster. Above an “adequate” tire pressure, the tire’s speed increases only very slightly with higher pressures. This contradicted the tests performed on steel drums, including those by TOUR.
  • Tires should not be tested without a rider on the bike. Most of the energy is lost in the rider, as vibrations cause friction in the body’s tissues (suspension losses). That is why testing in the lab can be misleading. In the lab, higher pressures roll significantly faster, but on the road, the suspension losses increase with higher pressures and cancel the advantage of the reduced tire deformation.

One important question was still open: Did the results represent real differences in tire performance, or was there too much noise in the data? After all, even slight changes in rider position, a tiny gust of wind, or other factors might influence the results. To check this, Mark, who has a Ph.D. with a Minor in Statistics, did a sophisticated statistical analysis. He found that our results were “statistically significant.” (Basically, he compared the data from the three runs of the same tire with the data from different tires. The variations between runs with the same tire were much smaller than the variations between different tires.) This means we really did measure differences in tire performance. (Many studies skip this step, but it’s crucially important.)

Our research had profound implications:

  1. Tire resistance is much more important than previously thought. For most riders, changing the tires is by far the biggest improvement they can make to their bikes’ performance. (Aero wheels will improve your bicycle’s speed by less than 2%, whereas tires can make a 20% difference.)
  2. On steel drums, wider tires were slower because they had to run at relatively low pressures. Once we had shown that the high pressures served little benefit, it became clear that on real roads, wider tires are faster, period.
  3. The secret to a fast tire is a supple casing. Compared to the casing, all other tire factors are relatively unimportant… In the past, many considered a high pressure rating as a sign of a “good, fast” tire. In fact, tires with high pressure ratings tend to need sturdier casings that make the tire slower.

Like most research that calls into question long-held beliefs, our findings first met with much skepticism, but over the years, they have become widely accepted. We used our research to help Grand Bois design supple, wide tires that offer more comfort and better performance than most other tires. Switching to these new tires, my  times in randonneur brevets decreased significantly. (I had been riding some of the slower tires in our test!) In addition, I no longer had a hard time keeping up in pacelines. (In a paceline, the air resistance is significantly reduced by drafting, and most of the resistance you have to overcome is rolling resistance.)

Today, even professional racers no longer worry about tire pressure. Their tires now are wider and run at lower pressures than those of most “weekend warriors.” And for the rest of us, this research has made it possible to build bikes with comfortable 42 mm tires that are as fast as racing bikes.

There still are some questions about tires that remain to be answered: whether clinchers truly are faster than tubulars; at what point the advantages of wider tires turn into disadvantages (it is unlikely that a 100 mm-wide tire rolls faster than a 50 mm-wide one), and whether tire deflection due to pedaling causes additional resistance when running very low pressures (in our tests, the rider coasted). We have been doing more research, and will report on it in future issues of Bicycle Quarterly.

Further reading:

About Jan Heine

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Rene Herse Cycles, that turns our research into the high-performance components we need for our adventures.
This entry was posted in Bicycle Quarterly Back Issues, Testing and Tech, Tires. Bookmark the permalink.

50 Responses to Bicycle Quarterly: Performance of Tires

  1. Greg says:

    Jan, this work on tires is, in my opinion, perhaps the most important thing you’ve ever done (in terms of bicycle-related analysis, anyways…). It has really opened many of our eyes, in the little niche of the cycling world where we live. Bravo. Now, more tests and follow-up data please! 😉

  2. GuitarSlinger says:

    Brilliant bit of research . Real World vs the Laboratory . The Lab coming up short on accuracy … as one would expect ( the multitude of forces/resistance etc imposed in the real world can never be fully replicated in a Lab . If they could , every F1 car on the grid would come out of the Lab a winner )

    A question if I may ? I’m wondering what the reason for the wider tire having better rolling resistance is ? I’ve always kind of suspected this to be the case from personal experience … so what is the technical reason why ?

    • There are two reasons the wider tire is faster:

      1. At the same pressure, a tire’s contact patch is constant, based on the load. A tire loaded with 100 pounds, pumped to 50 psi (pounds per square inch), has a 2 square inch contact patch. (In the real world, it’s a bit smaller, because the tire is not 100% elastic.) If your tire is 1 inch wide, the contact patch is 2 inches long. For a tire that is 2 inches wide, the contact patch is only 1 inch long. If you look at the drawing in the link below, you see that the shorter contact patch means much less deformation of the tire.

      2. In the real world, the wider tire runs at lower pressures, which reduces the effect of 1 a bit, but in return gets you much lower suspension losses.

      • Can you explain the difference in suspension losses?

      • The more your bike vibrates, the greater the suspension losses. So if you increase tire pressure, you reduce the deflection of the tire. This reduces the losses due to hysteresis. At the same time, the tire vibrates more, and you increase the suspension losses. On most road surfaces, the two effects roughly cancel each other. On very rough roads, the suspension losses are greater, and higher pressures make you go slower. Cyclocross and mountain bike racers have known that for a long time.

  3. Steven Shand says:

    Fantastic work and fascinating article. I’m off to put those fatties back on!

  4. Lucky cyclist says:

    I think that Frank Berto wrote in Bicycling-when he was technical editor-that at some point between 23mm and 28mm tires stop bouncing off of bumps and begin climbing over them, and that this is a large improvement. This is a distant memory that could easily be wrong; does this fit your experience?
    If I do remember correctly, he must have meant something like hitting a stone.

    • It probably depends on the size of your bumps, too. We haven’t tested identical tires in different widths beyond 25 mm, because at the time, there weren’t any available. We now are working on this, to see whether, for example, a 32 mm Grand Bois is significantly faster than a 29 or a 26 mm, all with the same casing and tread.

  5. Semilog says:

    Fantastic. I’d love to see how tubeless tires compare to other systems, and whether there are significant differences between different inner tubes. Since tubeless tires can be run with and without inner tubes, that comparison might also be interesting.

    • To our surprise, heavier inner tubes did not roll measurably slower. Latex tubes actually were slightly slower than butyl. Others have also have found that latex tubes roll slightly slower. No idea why. We haven’t tested tubeless yet.

      • Alex says:

        For the readers of this blog, i would argue that the main advantages of tubeless are the same for other riders: a reduction in flat tires (or better put: a reduction in the delays caused by air escaping from the tire, as the sealant closes the hole), not a reduction in weight and/or rolling resistance. If you are redesigning the Grand Bois rim section anyway, why not redesign them for the future, allowing for tubes/normal tires AND tubeless? The rim used on American Classic’s Road Tubeless wheelset is showing the way here: wide and lightweight rims that can be paired with any tire.

  6. Paul Glassen says:

    I have been riding Panaracer Paselas which I believe are from the same manufacurer as the higher quality Gran Bois (I hope to try them next). When you speak of supple casings, can you indicate where the Paselas come in and how they did if they were included in your testing? I use 32mm on my old narrower clearance bikes (c.1980 Colnago) and 35mm on my mid-’80s Gitane tourer.

    • Among budget tires, the Paselas were quite fast. We only tested the 37 mm version (35 actual) without Tourguard, and it was in the next category after the racing tires. For the complete results, I suggest you read the magazine article.

  7. BBB says:

    The whole rolling resistance / tyre width debate makes a fascinating if not scary study of human psychology and how people’s irrational BELIEFS are shaped by the world around them. Repeat a nonsense million times and will become a fact. History demonstrates all too well how brainwashed the masses can be.

    A while ago I naively believed that the internet would promote objective independent thinking and help shaping people’s opinions based on the wealth of information available to everyone via their broadband connection. Instead of debunking myths however the internet seems be an excellent tool for spreading “misinformation” (aka B.S.).

    Whenever I follow or participate in any debates regarding rolling resistance wheel inertia, weight and similar hot topics I feel that for many swimmingly intelligent(??) individuals the idea that most of their club mates, pros, magazine jurnos are simply wrong is inconceivable even when faced with hard evidence. People with a few thousand posts, spending weeks researching the fastest wheel options refuse to get some extra speed for free or for very little.(!)

    No offence anyone but I always had a strong impression that most of roadies seem to be only strong in a pack, both when it comes to riding and thinking;-)

    • GuitarSlinger says:

      “No offence anyone but I always had a strong impression that most of roadies seem to be only strong in a pack, both when it comes to riding and thinking;-) ”

      Too true . Thats been my experience over the decades as well . I’m sure if I were to forward Jan’s findings to most of the Racer Wanna Be Roadies I know ( and no longer ride with ) they’d be up in arms claiming ” Foul ” … ” doesn’t know what he’s talking about “.. etc etc . Then again they claim ‘ Foul ‘ when I go flying past them on a bike that’s anything but Racer Wanna Be . Truth sometimes is hard to accept : where as Dogma goes down smooth as silk 😉

      • I don’t think that is entirely fair. All new research should be viewed critically, ours included. Unfortunately, few people are able to review the evidence, and most just try to figure out: “Who in this debate looks most trustworthy.” More importantly, not all that many racers read Bicycle Quarterly, and you cannot expect them to buy the magazine just to read something they already suspect is wrong.

        What was a little more disappointing were the comments of some “experts.” One claimed that there was no reason for tires to behave differently on the road than on a steel drum, and that at infinite pressure, the tire would be fastest, because only the tread itself would deflect, while the main body of the tire would be totally rigid. When I pointed out that this would mean that a steel wheel would be fastest, the discussion went silent.

        Most tire companies also remain firmly wedded to their steel drums for tire testing. This is understandable – who wants to wait for a calm day when you have a deadline to get a product to market? Designing a real-road testing facility would be possible, but very expensive. (We’ve been thinking of paving abandoned railroad tunnels, which would have no wind, constant temperature, a constant grade, etc.)

        Fortunately, some of the technical advisers of professional racers are pretty smart, and when they saw our data, they knew what the implications were.

  8. BBB says:

    Just my 0.02p regarding tubeless.
    One of the huge and perhaps overlooked benefits of riding tubeless (at moderate pressures you don’t a dedicated tyre/system) is being able to use many fast and supple tyres with no puncture protection belts.
    A Stans sealant (it’s not worth using anything else) will take care of punctures without you even knowing about it.
    With a bit of shaving or clipping one could use some light and flexible high TPI XC or CX tyres.
    I honestly think that something like e.g. completely smooth Schwalbe Furious Fred tyre would have a chance to beat the best road clinchers for rolling resistance. Imagine the headline and the controversy… 🙂

    • In the past, Schwalbe’s tires always have been slow and harsh-riding. I don’t know about their latest offerings, but it does not appear that Schwalbe has casings that truly can roll fast.

      • BBB says:

        On MTBR forums there are some German bike mag tyre tests posted.
        Furious Fred and Racing Ralph are in the lead when it comes to rr.
        Some Conti tyres come close. There are so many fast XC tyres to choose from for experiments!

      • Much depends how you test. I know of one test that actually used a rider. If you test without a rider, you get results that are only of limited value.

        The other issue is which tires you compare. Most mtb tires have stiff sidewalls, and so the Schwalbes may not be any worse than others. I doubt they included truly supple tires in the test, such as the Dugast or FMB tubulars that many pros use. That would be an interesting comparison!

        For road tires, I always am amazed at the poor comfort of Schwalbe’s and Continental’s tires. They really are harsh. I haven’t ridden Michelin’s latest tires, but in the past (Pro2 Race), their high-end tires were a lot nicer in feel.

      • Fred Blasdel says:

        You absolutely should not speak from your experiences with their utility tires — Schwalbe makes a very full spectrum of tires, from absurdly stiff bricks that survive riding across central asia and back several times (Marathon XR) to world-class mtb tires so thin and supple they barely survive a single XC race (Furious Fred).

        The Racing Ralph really is a fantastic tire, if you read those german tests they find that it’s much faster than other top of the line tires despite having significantly more tread than many of them, the casing and rubber really is that good (also a hint that their testing protocol isn’t bullshit). Most of the popular high quality MTB tires are built in a number of variants to suit different terrain, casings from open tubular to butyl-reinforced foam, multiple rubber compounds of differing hardness and stickiness, optional sidewall and bead reinforcements, etc. — you get a lot of choices, not just width, puncture belt, and foldability.

        Their Kojak is pretty damn good despite the puncture belt, it feels faster than at least the Pasela TG and protects against more than just thorns. I’ve also got the new 28mm Ultremo ZX which I haven’t ridden yet but several friends are quite happy with. I’ve got quite a sizable collection of notable fast and fat tires you could borrow to test — many of them spares on the shelf including Road Tubeless and world-class time trial tubulars.

      • I have ridden a number of Schwalbe’s road tires on various test bikes, mostly their Stelvio and Durano models. They rode incredibly harsh – a 28 mm tire felt like a 23 mm. Perhaps their latest casings are better – we’ll consider testing them.

        Do you know anything about how they tested? On their web site, Schwalbe still has a graph that indicated that higher pressures made the tires significantly faster, something that does not hold true on real roads. This indicates that they still believe in the results of steel drum testing…

  9. Grant says:

    Very interesting read! And the big question is then: What tyres would you recommend? I’m currently on Contis GP4000S…

    • First, it’s obvious that I recommend the widest tire you can fit on your bike – the results are quite clear on that subject. Just going from the same tire in a 23 mm width to a 25 mm will bring you appreciably more comfort and a little more performance.

      Second, you want a tire with a supple casing. Beyond that, it’s nice to have a tire that lasts a long time. You’ll give up a little flat resistance, but wider tires already are much less flat-prone, so it’s not a major concern.

      Generally, you want to stay away from tires that are advertised as “flat-proof”, and from “touring” tires. Most wide tires unfortunately do roll slowly, because they use inexpensive, stiff casings. Only in recent years have some wide tires with supple casings like those of high-end racing tires become available.

      We sell the tires that we think are the best. (That is why we sell them.) Another tire that rolls very well is the Vittoria Open CX Corsa, but it appears to be a bit more flat-prone than the Grand Bois or Challenge tires.

      • David says:

        “First, it’s obvious that I recommend the widest tire you can fit on your bike – the results are quite clear on that subject.”

        I’m confused by this statement. Are your results actually clear beyond 25 mm? If so, why do you also state that:
        1) “We haven’t tested identical tires in different widths beyond 25 mm.”
        2) there are more questions that remain to be answered, including
        “at what point the advantages of wider tires turn into disadvantages”

      • The trend from 20 to 23 to 25 mm is so linear that it’s obvious that there isn’t a plateau anywhere near 25 mm. We also tested some truly wide tires, up to 42 mm, and found that they certainly aren’t slower than the narrower ones. So assuming you have a somewhat normal road bike, the widest tires you can fit will be more comfortable and either faster or no slower than narrower tires.

        Of course, if you ride a mountain bike, then this advice should be qualified a bit. And as I said, we have been doing more tests, so hopefully, we’ll have more results and more definite answers to these questions soon.

  10. SuginoSuntour says:

    Hi, thanks for the great article and taking the time to do this research. For the record, I love riding fatter tires for their comfort and rim protection. Just out of curiosity, what wheel set did you use between these trials? Were the hubs, spokes and rims consistent between every tire you tried?

    Furthermore, is there a way to account for a tire’s weight? All other factors held constant, don’t wider tires weigh more due to the increased material needed to manufacture it? Thus, I’m curious if a wider, heavier tire would keep more momentum as it rolls down the derby track, therefore making it “faster”? That being said, a wider/heavier tire may be faster rolling down a hill, but also feel more miserable to accelerate.

    • We used a number of wheels, because it is important to do the testing in relatively quick succession. We tested the same tires on different wheels, and found no difference in performance. (All wheels were 36-spoke with box section rims.)

      We did not account for the tire’s weight. That is the nice things about a track that slopes all the way: It’s not about momentum, but terminal velocity. With the slower tires, the bike still did slow down a bit, so a heavier tire would have a very slight advantage. On the other hand, the heavier tire also would accelerate more slowly at the beginning of the test, so it evens out. (We calculated this, and found that tire weight would have a negligible influence on the performance in our test.)

      We are working on replicating the tests using a different methodology. That way, we can exclude these problems with absolute certainty. (The drum tests really should have been replicated on real roads, too.)

      • The Magician says:

        I would also like to recommend for your next methodology to include some sort of blinding and randomization to try and remove rider bias as much as possible. Even though one may feel that are being impartial, rider bias and expected results could lead to unconscious body movement/positioning skewing the results e.g. ouija boards. Maybe some sort of crash test dummy since having a rider on the bike is important to the outcome of the results.

      • That is an interesting idea. We discussed this a lot when we first evaluated the tests. The interesting part was that a) the rider could not feel which tires were fast, and b) the tires we like and even those we sold at the time scored low in the test.

        So if there is a bias, it was against the tires we liked. The reality is that to produce a consistent bias (we did a lot of runs with several tires) would be very hard.

      • Thanks for addressing the weight issue. I had been thinking about that too after looking at a Dutch roll-out test which showed that wire bead tyres are faster than kevlar bead: Waarom draadbanden lichter lopen?

        Couldn’t they make the steel drum test more realistic just by making the drums a little bumpy and uneven?

  11. william says:

    Jan, have you tested or ridden Vittoria Randonneur Hypers (700c)? I have been riding these tires for one year now and I am generally pleased. They are worlds more supple and less sluggish than the Rivendell Jack Brown green label tires that they replaced…and even more supple/faster than the very slow Pasela Tourguards before those. I could even send you a pair if you’d like to try them.

    I will probably try the Cypres next, however.

    • We haven’t tested the Vittoria Randonneur Hyper. According to Vittoria, it weighs just 60 g more than the Grand Bois Cyprès in the same size, so at least there isn’t a lot of extra rubber. The “Triple Puncture Protection” makes me a bit concerned… Now if Vittoria offered the Open CX Corsa in wider widths (currently, it only goes up to 25 mm), that would be a tire!

      I also looked up the Schwalbe Racing Ralph tire. It’s a knobby mountain bike racing tire. It would be interesting to see a road version.

      • Fred Blasdel says:

        That road version exists, it’s called the “Super Moto”. It looks like a Big Apple with no reflective sidewall since it comes out of the same mold, but it’s built with a high quality casing and rubber instead of the utility crap, making it way more supple and hundreds of grams lighter.

        They’re simply ENORMOUS, measuring as big as 63mm on some fairly normal MTB rims.

      • Those tires do sound neat. Now we just need to find a bike on which to try them! A mountain wouldn’t work, as you’ll be compromised in the performance due to other constraints… I also wonder how you could fit a tire that wide between the chainstays of a bike and still keep the cranks relatively narrow and the rear triangle reasonably short.

      • Fred Blasdel says:

        It’s a perfectly pedestrian set of constraints for designers of dirt-going bicycles to have to work around, they usually shoot for significantly *more* room due to the clearance needed for mud (which means you can put fenders around a Super Moto!). Just because the performance is normally biased against your preferences doesn’t mean it has to be — my 650b Rawland rSogn has 8cm+ of clearance inside the chainstays, which are 44cm long, and can healthily clear standard 53-39 rings w/ a 145mm Q. It’s ludicrously excessive but the constraints really aren’t that hard to work around and the room for mud and chainsuck is welcome in a pinch. With some easy compromise on chainring sizes and some seat tube shenanigans the chainstays could be quite a bit shorter if that was felt necessary. This is all an exhaustively explored design problem in the world of 29″ mountain bikes.

        I have close friends with 26″ and 29″ Super Motos I imported for them, I’m sure they could easily be loaned for a test along with a number of other interesting tires, some of them set up as tubeless conversions. The sled doesn’t really need working brakes for the test, does it?

  12. Paul Richard says:

    My Compass 26×1.75’s are great! Any thought on whether the 26 x 1.9 (48mm) might become a reality? I’m convinced that this would be the perfect tire for my bike and riding (70% rough country roads, 30% unpaved roads). I’m considering a conversion from 26″ to 650B on my 1990 Koga Miyata Valley Runner (mostly to help balance the look and feel of the bike), but if the 48mm is on the horizon, I’ll wait for them.

    • Unfortunately, demand for fast-rolling 26″ tires still is relatively small. It seems that even though there are huge numbers of bikes with 26″ wheels, most are used either off-road with knobbies, or as inexpensive commuters with budget tires. True high-performance Allroad machines with 26″ wheels are still a rare breed, even though the size makes perfect sense in widths greater than 42 mm.

  13. Willem says:

    That is a pity. I have just returned from a loaded tour, with more than my usual load (25 kg rather than my normal 15 kg). I had fitted a Compass 26×1.75 at the front to try out, and an existing Pasela TG in the same size at the rear. The Compass was great, and the fastest and smoothest 26 inch tyre I have ever used. However, with the unusually heavy load I had to inflate the tyre more than where it shows its real strength. And it was on the narrow side on rough roads and trails. No punctures on the Compass, even though there sometimes was rather more glass than I liked. One puncture on the Pasela TG, but that was a big screw that would have defeated most tyres.

  14. David Lewis says:

    “On steel drums, wider tires were slower because they had to run at relatively low pressures. Once we had shown that the high pressures served little benefit, it became clear that on real roads, wider tires are faster, period.”

    I’m not sure I understand this comment. First, it sounds as if running at low pressures caused them to have greater resistance, then it sounds as if, on the road, that “greater resistance” went away, since higher pressures were deemed not to provide much benefit.

    You didn’t go into it very much, or maybe at all, but do you have any ideas why the drum testing produces such different results? I would think that one factor would be that on a steel drum, the contact surface would not be the same as on a flat road. That depends, of course, on the diameter of the drum. I would assume a sufficiently large drum would be a close approximation to a flat road. You do posit that the rider’s body’s reaction to bumps and vibrations absorbs energy, and I can imagine that to be true. It would be very interesting to isolate this effect, as perhaps riding style could enhance rolling efficiency.

    Finally, considering a smooth flat surface, such as a big drum or very smooth road, vs. a textured road such as one with chip-seal, one could imagine that the effects of suppleness might be even more pronounced and thus provide a broader range of rolling resistances between tires.

    • The problem with steel drums is that they measure only one half of the resistance – the resistance caused by internal deformation of the tire. (Basically, the tire gets hot as it deflects where it touches the road.)

      What the steel drums don’t measure are the suspension losses – the rider’s tissues that get hot as they rub against each other while vibrating. In a different experiment, we have shown that even on level roads, the suspension losses can be hundreds of Watts. The U.S. Army has measured suspension losses of 2000 Watts on vibrating tank seats…

      Putting bumps on the rollers won’t help. Yes, you get more tire deflection, but you still don’t measure the suspension losses. Perhaps if you put a bag filled with gel on the bike, you could replicate a rider? So far, the best strategy has been to test with a rider on the bike.

      You can read more about this in our blog post here.

  15. Evan says:

    Fantastic test! One question: “On steel drums, wider tires were slower because they had to run at relatively low pressures.” Why did they have to run at relatively lower pressures? (Running at relatively lower pressure is one of the things that wider tires are good at, right?)

    • The wider the casing, the higher the stresses imparted by the tire pressure. Imagine each inch of casing subjected to a certain pull. All the inches add up, and the longer the circumference, the greater the pull. This means that a wider tire must run at lower pressure, all other things being equal, otherwise, it would rip apart.

      On a steel drum, this means that the wider tire (at lower pressure) will be slower. On real roads, the lower pressure actually is an advantage, as it reduces the suspension losses.

  16. 2gross4u says:

    I like to climb. Added weight seems to make a bicycle descend faster, but added weight is the bane of climbers. When comparing heavy Vs light tires, wouldn’t results be different for a climbing test? The big problem is that unlike dropping a cyclist down a hill, a climbing test requires in finding a consistent power source.

    • Of course, you are right – physics are clear – but the question always is: How important a factor is this. Will going from a 23 mm tire (220 g) to a 42 mm-wide Hetre tire (410 g) cost me 5 minutes up a 1-hour climb, or 5 seconds? If it’s 5 minutes, then it’s significant. If it’s 5 seconds, then most of us don’t worry about it.

      We didn’t measure this – we were concerned about the resistance of tires on flat roads. But we have been working on the issue of climbing as well. In the Summer 2012 issue (now at the printer), Bicycle Quarterly will look at what wider tires, as well as fenders, lights and a rack, will do to your climbing and sprinting. We look at theoretical calculations, as well as some on-the-road experiments.

  17. O.Pool says:

    “For road tires, I always am amazed at the poor comfort of Schwalbe’s and Continental’s tires. They really are harsh. I haven’t ridden Michelin’s latest tires, but in the past (Pro2 Race), their high-end tires were a lot nicer in feel.”
    I am quite surprised to read this, as my personal experience with road tires (700C, sizes 23-28 mm) is about the opposite: I had a very poor comfort with all Michelin tires I have tried (especially the Pro3 Race), liked my old (Schwalbe) Stelvio’s, and I could never find any better comfort than my Conti 4Season’s (still searching, but no tire in this category has ever come close)
    In another post you mentioned Vittoria’s tires’ qualities: I nearly put them in the trash after a few rides, as they were the most uncomfortable I ever tried.

  18. bc says:

    Neither here nor there really, but I race as a local Cat 3, and for the first two months of the season, I used Challenge Parigi-Roubaix tires (700x27c listed, and as they sit, more like a 28 or 29 on Open Pro rims). They fit with room to spare on my Cannondale CAAD10 (with the brakes set up so I could roll the barrel to get the wheel out), and they rode and raced great. I pulled several top five finishes, including winning a handful of bunch sprints and such. I wasn’t out to prove anything, mind you, I just had the tires on there from the months before, and they rode fast and well enough that I didn’t feel like there was a need to change them.

  19. Sky King says:

    I switched from Nifty Swifty to Gran Bois Hetre’s for a 105 mile tour on dirt roads. I was concerned about flats so I did put Mr Tuffy liners in prior to the ride. But even with liners these tires roll beautifully, so much so that I am leaving them on and buying wider fenders to accommodate. Another thing I have noticed is better all around riding performance. I have become more precise in my gearing as the tires “bounce” quickly lets me know it’s time for a gear change. While speed isn’t important to me, I do ride faster and I hadn’t even read this article yet 🙂

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