15

My question is in regard to typical bicycle wheels one might find on a road bicycle. I own an old second hand road bike, and after many spokes started to snap while riding it, decided to replace the all the spokes myself. This was the first time building a wheel, but I think that after a bit of trial and error I eventually seemed to have a fairly good wheel. That is, until I warped it by putting a decent amount of lateral loading on it. Basically, I was riding the bicycle slowly while putting the bike at a large angle to the road (think about 45 degrees, riding straight). Eventually, I heard a creaking noise and the bike stopped, forcing me to fall off. After looking at the bike both wheels were severely thrown out of true, and when trying to re true the bike, I noticed that the spoke tension needed to be very uneven to get the rear wheel back into true. I haven't taken the wheel apart yet, but I am guessing that thanks to my little stunt, I had plastically deformed the rim of the rear wheel. What I am not sure about is, is it just expected that road bicycle wheels are just not designed to handle large amounts of lateral stress? Under normal bicycling conditions, there shouldn't be so much. Or, would it be possible that there was something wrong with my wheel, as since it was the first wheel I had built, I wouldn't put it past me to not build a good wheel the first time around. For instance, I am not confident if I pre-stressed them enough, and it is hard to tell how much the spokes are expected to "stretch out" over time.

I remember I would do similar stunts on my mountain bike back when I was a kid, but this was when I weighed less, and the wheels were a bit beefier and smaller diameter than the wheels that I ride on now.

Basically, I am wondering if bicycles are designed to handle these loads or not, because I want to make sure my bicycle is as strong as it should be.

I appreciate your time and valuable advice!

Improve this question
7
  • 2
    If you can lean over while riding without just plan falling over, then yes your bike and wheels should be able to take the load. Remember that in normal riding that while leaning going around corners, all the loading isn't perpendicular to the ground. Sorry to say but I would suggest the spoke tension wasn't right
    – Hursey
    Jul 3 at 2:56
  • 5
    @Hursey cornering doesn't put lateral loads on wheels. Cornering without leaning would do that.
    – ojs
    Jul 3 at 7:22
  • 1
    The lateral strength of a 'normal' bike wheel is surprisingly strong - I've seen people standing on the side of them without them going out of true. As this was your first time building a wheel, I'm relatively sure it probably needed to be done more carefully. Wheel building is a real skill and not something I'd ever consider even trying as it's a bit dodgy if you wheel does something strange like in your case. I suggest finding a professional to help guide you, but until then there's a load of good videos from 'moustache man' from park tools that you should check out.
    – John Hunt
    Jul 3 at 10:36
  • 1
    Your wheel was probably compromised, since you rode it for some time with n snapped spokes, with n = (many - 1).
    – EarlGrey
    Jul 3 at 14:32
  • 2
    Something like this: i.imgur.com/jKESDEi.png. We used to do that as kids.
    – nathancahill
    Jul 4 at 10:48

4 Answers 4

Reset to default
9

Welcome to the site! Nicely written question.

For starters, your bike shouldn't have broken under what were (more or less) static conditions. It's not like you hit a bump and that bent the wheels. You're lucky they failed now and not while zooming downhill and encountering said bump for example. Spoked wheels can be really strong in the lateral direction--for example, look at mountain bikers landing jumps with the wheels angled away from the direction of travel. The peak load in such a scenario is much greater than what yours experienced.

Unfortunately, I think the most likely explanation here was that you built the wheels incorrectly. Many, many cyclists (even on ultralight carbon race wheels) put large, dynamic lateral loads on their wheels, and yet failures like this don't happen that often. As suggested in a comment, it's possible your spoke tension was significantly off, which could have resulted in spokes entirely losing tension and bad things following suit.

Now for diagnostic questions: how did you build the wheel/what guide did you follow to do so, and how did you verify spoke tensions? What rims do you have, and what are the spoke counts? And just how out of true are we talking about after the wheels failed? Do you see any damage to the spokes/hubs/rims?

Inadequate stress relieving is going to affect the long-term lifespan of the wheel and its ability to stay true, but it's not really going to impact the possibility of a sudden failure like you described. Same goes for initial spoke stretch (which with proper stress relieving, should be minimal anyways).

Improve this answer
8
  • 1
    Mountain bikers who land angled can and do often taco their wheels, even high-quality ones. It's true that such a landing puts more stress on the wheels than the OP's experiment, but then again the OP's rims were likely weaker than even a superlight wheel. (Carbon is stronger than aluminium, contrary to what some voices say, and that gap gets even bigger with fatigue.) So, I wouldn't jump to the conclusion that this was an incorrect build. Note in particular that lateral forces are much more the rim's responsibility, unlike vertical forces which are almost completely carried by the spokes.
    – leftaroundabout
    Jul 3 at 19:07
  • @leftaroundabout Would lateral applied forces not result in an increase in spoke tension on one side and a decrease on the other? I suppose the rim is in danger of folding over and resulting in a taco in that case. It is likely true that OP's wheels wouldn't be super strong even if built right, but I'm struggling to imagine that any correctly-built wheel currently sold on the market would be expected to fail under such a scenario. I don't think even the lightest aluminum road bike wheel would be expected to fail like that.
    – MaplePanda
    Jul 4 at 4:05
  • for a wheel with infinitely many spokes, yes, even the lateral loads would be handled completely by a tension increase of the spokes coming from the bottom-facing side of the hub. But this inefficient, because the hub is not very wide compared to the wheel size (forces are multiplied by a factor >10), and also only every other spoke comes from the right direction, so even for a well-built wheel with many spokes there remains a significant bending moment that must be handled by the rim alone.
    – leftaroundabout
    Jul 4 at 8:08
  • Thank you for the great answer! I hope I am doing this right by responding in the comment section. I followed several YouTube videos, like the famous park tools one and the famous "anyone can build a wheel!" video. When I build the wheel initially, I tried to use the pitch of the spoke with a tuner on my iPhone, but it was tricky to isolate the pure frequency of a spoke from the other resonances it coupled with (like the spoke laced with it), and It was kinda a slow process. 32 spokes, and what I assume is an anodized aluminum rim. The wheel was maybe a few millimeters out off true.
    – Eliot Foss
    Jul 4 at 8:45
  • @EliotFoss that's not a durable wheelbuild. Adequate wheels are laterally off true about 0.25 mm. That's the accuracy to which I build my wheels, since I only have a cheap wobbly truing stand. I'm sure someone could do it to an accuracy of 0.1 mm with a very sturdy truing stand. Also, I have never been successful in comparing spoke tone to some reference tone with specified Hz. Best to buy a tensiometer or compare to a reference wheel. Besides, since the spokes cross each other, calculating the correct Hz value is not as easy as it may sound.
    – juhist
    Jul 4 at 14:21
6

I agree with the other answer (https://bicycles.stackexchange.com/a/89517/33932) that you had inadequate spoke tension. It should be possible to put all reasonable lateral loads on a bike wheel that can happen on normal riding. However, in accidents these kinds of "tacoed" wheels can and do happen. The less spoke tension you have, the more likely is it.

What was not specified on the other answer is whether you can repair the wheel. It's possible it can be repaired, but it's possible that your straightened rim results in a somewhat nonuniform spoke tension in the repaired wheel, which could reduce the durability of the wheel. It's worth trying, however, because it will save a significant amount of money (no need to purchase a new rim) AND time (no need to re-lace the spokes).

Since you build wheels yourself, surely you have bought The Bicycle Wheel by Jobst Brandt, haven't you? It has instructions for repairing this kind of damage in page 114 (third edition of the book).

Basically you untighten all of the spokes by several turns of the nipples, force the rim back to its original shape as well as you can, and then rebuild the wheel, this time using proper spoke tension. If you don't have a reference wheel with identical (same thickness, approximately same length) spokes that you could pluck and compare the tones, then a spoke tensiometer is a good investment.

I suspect nipples in your wheel would have untightened gradually, meaning the spokes would have lost tension at some point automatically. That happened to my first wheelbuild -- inadequate spoke tension. Your stunts apparently caused an entirely different failure mode, though: a tacoed wheel. Still, it wasn't a durable wheel, it may have seemed durable but it certainly wasn't.

Also, after building remember to stress relieve all spokes. This is the most likely explanation of the snapped spokes: your old wheel may not have been stress relieved. Instructions for this can be found in The Bicycle Wheel, too.

Improve this answer
4
  • Ah, thanks for the recommendation on the book! I found a copy online, and the section on "SOFT WHEEL FAILURE" is exactly what I am looking for! I agree a good tensiometer is a nice investment, but being the frugal person I am, I might just jerry rig one myself. Furthermore, I did compare my spoke flex to other bikes, and it seems as though my spokes seemed just as taught, but it is not easy to tell for sure. Yes, I tried to do stress relief on the wheel I had built. I bought the bike second hand, so I assumed the wheel would be good, but maybe I assumed wrong.
    – Eliot Foss
    Jul 5 at 6:02
  • Sorry I couldn't fit it in the last comment, but I actually built the wheel using no lubrication, which in hindsight was not a good idea. But because of that I think the nipple would be less likely to loosen over time like you suggest.
    – Eliot Foss
    Jul 5 at 6:03
  • 1
    Nipples should be lubricated, because if a spoke completely unloads, the nipple will self-unscrew no matter whether it has lubricant or not. However, if the spokes never completely unload, no nipple will loosen. Some people try to combat nipple loosening by gluing them. While that sort of "works", it's not good design. Good design is a wheel where no spoke ever completely unloads, thus the nipples can't self-unscrew. In all machinery, screw joints are lubricated and they don't self-unscrew if the screw joint is properly designed.
    – juhist
    Jul 5 at 15:42
  • You might need to be more specific about which other answer you're referring to at the beginning. Ideally, you could link to it (use the "share" link below the answer to get a permalink).
    – Toby Speight
    Jul 20 at 11:58
2

So, after removing the rim from the spokes and tire, I can confirm that the rim is now slightly bent out of shape. This explains why I needed to use uneven tensioning after the incident. The issue is that when building the wheel, before building, I checked the rim and it seemed fine. I am pretty sure the rim bent due to this incident, as I never crashed the bike, and before the incident I am certain that the wheel had been true, and the tensions were more or less even (by using the frequency/pitch of the spoke vibration). I had ridden a good 100 km on the bike after building both front and back wheels, with no sign of either wheel losing trueness before the incident, so I can't think of anything else that would have caused the rim to deform permanently. The only question is, was the tension in the spokes too low? Or was my rim just not strong enough for this amount of lateral loading?

It may be hard to find a definite answer, but I decided to do some research, and found a nice PhD thesis written by Matthew Ford on wheelbuilding, optimization, and wheel strength: Reinventing the Wheel: Stress Analysis, Stability, and Optimization of the Bicycle Wheel The author also put up a nice website with a calculator for doing loading calculations on bicycle wheels: https://bicyclewheel.info/wheel-simulator/ I could measure out the relevant dimensions of my wheel and input into the simulator (e.g. 32, 13 gauge steel spokes, asymmetric offset, etc.) and have it calculate spoke tensions and deflections using point loading on the wheel. The only things I couldn't easily measure is rim stiffness, so I just picked the pre-defined Alex Y2000 700C rim since it seems to match my rim for the most part. The calculator give a convenient estimate of "Lateral force to buckle spokes" as a value of 30 kg. And when simulating a combined radial and lateral loading each 25 kg, the spokes start to reach very low tensions. Whether this results in permanent deformation of the rim is not clear, but I assume that stressing the wheel to the point that spokes start losing tension is never a good idea. Given that, I weight about 80 kg, and probably close to 85 with my clothes and backpack on, it is entirely possible that I did put too much stress on the back wheel (especially since I was leaning onto the drive side of the wheel where the lateral stiffness might be weaker).

I think that for now I at least know that I should probably leave the crazy stunts to the BMX bikes and not pointlessly try to damage my bike in the future. If possible, I will attempt to bend the rim back into shape, but that is easier said than done (how do I know the rim is in the right shape? Would it still be safe to ride?).

Improve this answer
3
  • Also for those interested in truing wheels, Ford also wrote a nice article on it in the same website: bicyclewheel.info/articles/wheel-truing
    – Eliot Foss
    Jul 5 at 5:41
  • There appears to be another question nested within this answer, e.g., spoke tension.
    – Ted Hohl
    Jul 5 at 18:33
  • Do note that aluminum rims don't necessarily come perfectly straight from the factory. They're made by extruding the rim profile in a large helix, cutting loops from that helix, and then joining the two (offset) ends of the rim. This necessitates some bending, which may result in inaccuracy, especially at lower price points. It's generally acceptable to sacrifice some level of spoke tension evenness in the pursuit of a straighter wheel, but at the same time, it's not important to have a perfectly straight wheel either. Some wobble is usually unnoticeable in normal riding.
    – MaplePanda
    Jul 5 at 20:09
1

An aside: I sometimes ride trikes as an alternative to bikes, and they don't (normally) lean for cornering, and so they put more lateral stress on the wheels than a bike. I haven't had problems with spokes breaking or rims warping on "full-size" trike wheels (27" or 700c) but have had quite a few broken spokes on the small front wheels of recumbent trikes. As you describe the bike as a "road bike", I'll agree with the previous answers; if it were a small-wheel bike, such as a folding bike, I think the spokes might be more vulnerable to lateral loads.

Improve this answer
3
  • Note that because a trike can't lean into corners it also can't corner as hard (or it would risk tipping); the question was also about the rim bending as opposed to spokes breaking.
    – DavidW
    Jul 4 at 14:15
  • 2
    Small-wheel bikes are usually less vulnerable to lateral loads if the over locknut dimension of the hub is the same, but wheel diameter is smaller. Then the spokes are at more of an angle, which helps with sustaining lateral loads.
    – juhist
    Jul 4 at 14:15
  • I also agree with juhist's comment. But, it depends on many factors. It would be interesting to find out how many "Gees" you pull when turning hard in one of your tricycles, or if the tricycle wheels are designed differently from typical road bike wheels.
    – Eliot Foss
    Jul 5 at 5:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.