Weight Limits?

cyclist_puffing

We sometimes get the question whether there is a weight limit for Compass tires or components. The answer is “No”. That doesn’t mean that our components are indestructible. It’s just that we have found rider weight to be a poor predictor of component failure. Neither is power output.

Heavy and strong riders, who pedal smoothly and ride “light”, rarely break components. On the other hand, there are light riders with modest power outputs who tend to destroy components. So instead of simple weight limits, we ask you to look at each part and your riding style.

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For tires, there is a weight limit of sorts: the maximum tire pressure that the casings can support. Your tire pressure is related to your weight, and if you don’t inflate your tires enough, you will get pinch flats. Our wider tires have a higher “weight limit” than narrow ones, even if their maximum inflation pressure is lower.

For example, Compass 38 mm-wide tires have a maximum inflation pressure of 75 psi (5.2 bar). At the maximum pressure, these tires will support about 150 kg (330 lb) of bike/rider weight. Our 26 mm tires have a maximum inflation pressure of 105 psi (7.2 bar). At that pressure, it will support about 110 kg (240 lb) of bike-cum-rider. There is a margin of safety in these numbers. You can overinflate your tires a bit (say 10%) if your rim is within normal tolerances. And if you weigh a bit more, your tires will deflect a bit more, too. That isn’t ideal, but usually it’s fine.

This is especially important for tandems. It’s pretty much impossible to find a good tandem tire that is narrower than 30 mm. A narrow tire that can support the pressure required for the weight of a tandem team will be harsh-riding and relatively slow. However, if you go to a 38 mm tire, you’ll find that most tandem teams can ride them at the 75 psi for which these tires are designed.

(Of course, if you weigh less, you should inflate your tires to lower pressures. The limit is just the maximum, not the recommended, pressure.)

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For components, it’s trickier. Compass components are high-performance parts intended for spirited riding. We test our components to the highest “racing bike” standards for fatigue resistance, but that does not mean that they are indestructible. If you are a rider who has a history of breaking parts, then our components may not be suitable for you.

We could make our components strong enough for the riders who are hardest on their components. However, that would make them so bulky and heavy that they no longer would appeal to the other 90% of riders. It’s a trade-off, and we want to be honest about it.

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So if you are a “normal” rider, even a very strong one, you probably will have no problems with our components. Compass parts are designed to the highest standards in the bike industry, and tested to the most rigorous “racing bike” test protocols. (Unfortunately, that can’t be said for all “boutique” component makers.)

And for everybody, it’s a good idea to work on a smooth pedal stroke and on “riding light” and working with the bike, rather than let it crash into the irregularities of the road. It makes you a better rider, it makes cycling more enjoyable, and it makes your components less likely to break.

About Jan Heine, Editor, Bicycle Quarterly

I love cycling and bicycles, especially those that take us off the beaten path. I edit Bicycle Quarterly magazine, and occasionally write for other publications. Bicycle Quarterly's sister company, Compass Bicycles Ltd., turns the results of our research into high-quality bicycle components for real-world riders.
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35 Responses to Weight Limits?

  1. Greg says:

    This subject is very interesting to me. I’ve gathered actual breakage data from a large group of enthusiast cyclists in the past. Not ” I had a friend who had a friend who had a cousin that I think broke a crank arm ” data, but actual, personal ” I broke a ….. while riding” data. I did it mainly because I was curious about crank arm breakage, so in those specific cases I asked riders to tell me where on the arm the breakage occurred (it was almost always a bit above the pedal eye, at or near the smallest cross-sectional area region of the arm, regardless of part brand, and lots of brands were mentioned), the total mileage on the part (if known), as well as whether they had broken other parts, and if so, what those parts were.

    My findings were that a very, very small percentage of riders (maybe 1-3%) break all sorts of things: crank arms, pedals, bottom bracket spindles, chains, spokes, hub flanges, freewheels, handlebars, stems, saddles, seat posts, and frames. Yes, frames. The other 97-99% of riders have never broken a single component in their lives, apparently. The breakage did not correlate to rider weight or experience level.

    My preliminary conclusions were that in general some people may have a particular pedaling style that causes very high cyclical stresses in bicycle components, for some odd unknown reason unrelated to their weight or power output, and that other than due to obvious defects in a crank arm like a void in the casting or forging, failures in those particular parts typically occur at very high mileages. Additionally, almost all of the crank arm failures were drive-side parts, with a few exceptions. One fellow broke his 50,000+ mile RH arm, then kept using the matching LH until that also failed!

    • Greg, interesting data. Can you give us the n for your crank failures. It seems that a lot of these probably were Campagnolo Nuovo/Super Record cranks… Interestingly, most crank failures I have seen were non-driveside (left side). I agree with your assessment that riders who break parts aren’t necessarily strong, however, I’ve seen some failures in relatively short time (less than 20,000 miles)…

      I think it’s important to rigorously test components before offering them to the public. Our Herse cranks certainly have seen a number of modifications based on these tests, so that they now pass the most stringent EN standard for racing bikes.

      • Greg says:

        I’ll dig that data detail out (if I can find it, it was many years ago…). It was all sorts of brands: TA, Campagnolo, Stronglight, Sugino, Zeus, Shimano, Ofmega/Avocet, and maybe a few others that I am forgetting. The group that I queried was over 1000 riders, and I tabulated their various inputs for about six months or so, as I vaguely recall. One rider broke several crank arms, of several brands! He also broke other parts like a BB spindle, and a freewheel, maybe even more, if I recall correctly. Another fellow broke multiple steel frames, plus I think a few other components, in addition to a crank arm. I presume you’ve seen Damon Rinard’s broken crank page on the Web?

        We are currently testing one of our new Heron frames and its fork to the EN standards, fwiw. That should be completed by the end of this month, I think.

    • One fellow broke his 50,000+ mile RH arm, then kept using the matching LH until that also failed!

      I assume the 50,000+ mile Rene Herse arm was one of the original ones from the 1940s-1980s, not one of the cranks Compass offers.

    • B. Carfree says:

      I don’t break many parts; I wear them out. However, the one “part” that I break with regularity is the frame. “Yes, frames.” I’ve had six frame failures over the years, which works out to about one every 100,000 miles. However, three were seat tube failures at the bottom bracket (one a tandem) that simply failed from fatigue. The other three were old Trek frames with a well-known weakness at the top of the seat stays. There just wasn’t much metal there the way they used to do that joint.

      I’ll say this about steel frames: I’m not unhappy with their mode of failure. I’ve never had one fail in such a way that is caused me any issues other than the need to repair it.

      • Obviously, poor design will lead to failures even under riders who “don’t break” stuff. The afore-mentioned 1970s Campagnolo cranks are a good example, or the first generation of Sun XCD cranks, which all seem to have failed. In both cases, rigorous testing would have pointed out the weaknesses before the products were released.

      • Greg says:

        Seat tube failures at the bottom bracket are almost always due to overheating during brazing (unless they pull out due to insufficient heating and lack of brazing material – I’ve seen one do that, over the past fifty years – a Trek, during a criterium race). What were the three frames in question, and who built them?

      • Greg says:

        Jan, I have some Sun XCD cranks. What was the issue, and how do I tell first-generation ones from subsequent ones?

      • I think it was a stress riser at the back of the right crankarm, where it was machined to meet the spider. I am not that familiar with the various budget cranks on the market, I just heard both in Japan and in the U.S. about the high failure rate as soon as these cranks were starting to accumulate a few miles.

      • Greg says:

        P.S. The “1970s Campagnolo cranks” don’t fail at high rates. Far from “all of them” have failed. Please don’t say silly things like that without having any data to back it up. Perhaps 3% of them fail, over decades, vs. about 1% for most other (non-CNC’ed) forged cranks. Still very low failure rates in both cases. And very few of them fail at the “dreaded spider-crack area….” There is far too much urban myth involved in bashing Campagnolo….. I have the data. 🙂

      • Sorry, the “all of them” comment was intended to pertain to the first-generation Sun XCD cranks. Still, if true, a 3% failure rate for the 1970s Campagnolo cranks would be shockingly high. If even 1% of our René Herse cranks failed, I’d recall them immediately.

        I don’t know how you got the sales and failure data for these cranks… but I doubt that classic TA or Stronglight cranks had a failure rate of 1%. As I said above, that would be terribly high.

      • Matthew J says:

        It would be interesting to see the crank fail data as well.

        If we are talking actual customer experience and not quality assurance testing, I am skeptical a sufficient number of cyclists from that era would report back to the manufacturer (or survey company).

  2. heather says:

    I never really thought about weight until recent years. As a tiny person I would wonder why I struggled so much on my bikes. Standard bikes, meant for larger people, often far too heavy. Lighter components make a huge difference and wish I’d sorted this out sooner in life. Some people are just clumsy, or break things, all kinds of things no matter what! For some reason my husband has had terrible luck with tires for the last few years. Grand Bois tires in particular which is funny because so many swear to have few problems with them. Even schwalbe tires have gotten endless flats. He is very light, so is it possible he’s over inflating tires, or under inflating?

  3. Gunther says:

    Just rename non-driveside crank after Lyli Herse, LH.

  4. Ted kelly says:

    As in “nm”, now is that nano meter or nautical mile. Usage and context usually make it clear but still …

    • Dave says:

      Neither. “nm” stands for “never mind”. In the context of torque, it means to just snug it up and never mind getting the torque wrench out.

  5. John Hawrylak says:

    Re max weight for the 38mm/26mm tires (330#/240#). Are you using different AREAs the pressure is applied to get the weight for the 2 tire widths?? The 38mm at 75psig = 2.2sqin assuming the 340# is spread on 2 tires. The 26mm comes out to 1.4sqin. The 26mm has significantly smaller area

    John Hawrylak
    Woodstown NJ

  6. John Duval says:

    I would love to see more on who breaks what and how, as unlikely as that would be to get. I never thought myself to be in that 1%, having broken several spokes and nipples, a few chains (MTB only) and a freehub as an adult, and most everything else as a kid on BMX bikes. Each failure I had attributed to a specific cause, though the research above suggests I played a more significant part. Poor component choice was certainly part of my contribution.

    Having a crank break is a very ugly way to crash, lucky to escape with only bad bruises and deep road rash. I never crashed from any other drive line failures because at least my feet were still on the bike. My new TA Carmina cranks don’t look very strong, but appearance is a poor guide.

  7. Herb Bloomer says:

    Most tandem teams & bike are over 350# and have used 700x 28’s at 120psi for years. Most could use 700×32 but no larger will fit. Your tires are for 1/2 bikes only or little people [120lbs + 180lbs + 30lbs =330] no water and no tubes.

    ]

    • You are right, 38 mm tires are at the limit for heavier tandem teams. That is one of the reason why the new Rat Trap Pass 54 mm tires have been popular with tandem riders. With those, even a heavy team won’t need to run them at the maximum inflation pressure of 65 psi…

      Of course, if your tandem cannot fit wide tires, then you are stuck with using tires that have sturdy casings, so that they can accept high pressures. Unfortunately, those tires will ride harsher and slower than tires with supple casings. Using sturdy tires on a tandem that is designed for narrow tires is a necessary compromise – we all ride the bikes we have, not the ones we wish we had.

  8. David Pearce says:

    Comment on the illustration.

    I assume he’s French, a rider of substantial carriage, shall we say. He wears a watch in his left pocket (I assume), the fob attached to his belt. At least he is faster than the snail.

    He rides a well appointed touring bicycle, with front & rear panniers, fenders, & lights. Actually, the way the horizontal part of the stem is drawn intrigues me, with three short vertical lines. What do they express in particular, if anything?

    He “ankles” well, at least with his right foot. He appears to be huffing & puffing, judging by his apparent breath, pedaling both a fully loaded bike and fully loaded belly. Or maybe he’s just whistling, or whistling AND huffing & puffing. He looks happy.

    But what is he carrying in his right hand? Something to eat, do you think, a piece of bread, a package of cigarettes, a bon-bon or petit-four? Or a stop-watch or a whistle?

    Every part of the stylized picture stands for something real, just in abbreviated form. I want to expand those abbreviations to full size words!🙂

    Thanks for all your wonderful things.

  9. Michael says:

    Speaking of Compass tires. Will a narrower Compass tire have less rolling resistance than a wider one just based on the fact that there will be less tire touching the ground?
    This question sounds simplistic, but in light of the claim that one does not lose speed with a wider tire, I’m wondering about tires of the same make in this case.
    I am under the impression the 650b Compass tires are the same tire just in different widths.
    What if there was a 32 Compass 650b? Less RR than a Loup Loup?

    • We have measured rolling resistance for tires from 21 to 31 mm wide. We found that 21 was slowest, 23 second, 25 – 31 all the same within the measurement tolerances. The latter data (25-31 mm) was for smooth roads.

      We also measured on rough roads, and found that wider tires do roll faster. So we don’t really know whether a 38 mm tire will be (slightly) slower than a 32 on smooth roads, or about the same. We do know the wider tire is faster on rough roads.

      How wide can you go before you lose performance? With the new Compass Rat Trap Pass (26″ x 54 mm) and Switchback Hill (650B x 48 mm), we finally are in a position to test this…

      • Michael says:

        Have you tested tires in the 32-42 range yet?

      • We haven’t. Until the Compass tires became available, there were no tires with the same casings and tread design in those widths… We decided to wait until the really wide tires became available, so we could test from 32 to 48 mm wide tires on the same wheels. Now we just need perfect conditions for testing (no wind, constant temperature).

  10. woahdae says:

    Just to be specific, and out of curiosity borne from adding 40-50lbs up front sometimes, a sanity check for a porteur:

    The weight limit for a single tire, say a 38mm, is 165lbs? So if my body were at 200lbs, with a weight distribution of 45% front 55% rear, the maximum weight I should put on a porteur rack with a fully inflated 38mm tire would be 165 – (200 * .45) = 75lbs? Quite reasonable.

    The new RTPs on a portuer would be even better! Stronger rim too.

    • The weight limit for a single tire, say a 38mm, is 165lbs?

      That is correct.

      The weight limit is somewhat flexible, because it’s really a maximum pressure. You could load up the tire more at that pressure, but it might start to feel sub-optimal when you corner at the limit.

  11. Luis Bernhardt says:

    Back in the 70’s, I broke about six cranks in roughly 8 years. They were all brands – Sugino, Shimano, Campag. I weighed 170-175 pounds then, as now. Usually the cranks (almost always the right) would break during autumn (I hesitate to say “in the fall,” as this might be ambiguous). I finally figured out why they were breaking: I had been riding the cranks during the Pacific NW winter, where a lot of salt gets dumped on wet, slushy roads and it gets kicked up to the cranks. If I did not wash off this road salt, it work work its way into the aluminum, and a few months later, usually in the autumn, the crank would break. As soon as I started washing off the cranks with a bucket of warm dishwashing detergent when I arrived home from my commute or my training ride, the breakages stopped. However, I did recently break a SRAM Omnium track crank, right at the pedal eyelet. It had been used during my winter commutes, and broke in the autumn, so I guess I wasn’t paying enough attention to washing off the road salt…

  12. Timothy Tetrault says:

    Any tips on ‘riding light’?

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