A twenty-something male had a terribly painful crash for no apparent reason on a perfectly smooth and clean stretch of blacktop. It was an ugly scene and I failed to get any details about his bike except that one front wheel spoke was broken at the nipple and gone, and the front wheel was rubbing hard on the brake. It was the lightest bike I ever touched and had the fewest spokes I've ever seen. Could the spoke have broken first, let the wheel out of true, and dumped the poor guy off? I saw the crash from 75 yards behind and would like to know if the modern wheel failure could be the cause.

I suppose your analysis could be correct. A low spoke count wheel can indeed go wildly out of true if a spoke breaks and it might rub against the brake shoe hard enough to slow the bike suddenly. This would be even more likely if the brake shoes are set very close to the rim.

Spoke failure in a low spoke count front wheel? Sure, that could cause an immediate crash. Who built the wheel?

Sure it could. How fast was he going? Even at 20 mph a speed wobble could make you fall. Which could happen if the spoke broke on a low count wheel.

I've never seen a brake rub hard enough to cause a crash, though it's possible with double pivot brakes which have less horizontal float. OTOH, if a wheel is untrue enough the tire can rub the fork blade hard enough to stop the bike and cause an endo.

This risk, and that of squirrels or road debris getting jammed between the spokes of low spoke wheels is why I won't use them for front wheels. These kinds of things are rare, so they don't rank high on the table of risks, but since I don't ride competitively I see no need to take them on no matter how small.

I didn't have a broken spoke or even an untrue wheel at the time, but a couple months ago I was riding a nearby stone dust bike path and mysteriously crashed. The last thing I remember was running over a stick, which I've done many times before (my hybrid has 700x35c wheels and I usually have no issue). Picked the bike up and found the rear v-brake lodged in the wheel. Still unconfirmed, but I'm guessing what really happened was when I ran the stick over, the knobby tires in the rear grabbed it, knocking my balance out of whack and caused me to fall. I probably will never find out how it happened, but I managed to get back on the bike and finish off the 30 mile ride (~15 miles left) slower than usual since my knee was in pain from the fall.

It's rare for rear wheel obstructions to cause a surprise fall, though it may happen if the wheel suddenly locks up at decent speed, such as when a stick is jammed in the spokes and carried up to the stays.

However crashes due to steering issues are very common. Sticks, large pods like chestnuts, and round stones can cause a crash by rolling under the tire and displacing the front wheel sideways a few inches. Immediate corrective steering is needed, and if you're not alert or have a loose grip on the bars this can bring you down quickly and unexpectedly.

Crashes due to loss of steering control are far more common than those caused by something in the rear, but both can happen. These are the risks of riding on something which requires keeping the center of gravity directly over a narrow track.

I guess its my 35 years in the chemical industry where I cannot attribute a crash to a broken spoke. Its the old "ask why five times?" For instance, "why did the spoke break?"

Ultimately, most accidents have a half dozen or more root causes, which could include the proper selection of the spoke and type of wheel for the kind of riding, the maintenance of the spoke and nipple, tire pressure, wheel rating versus rider weight (my problem), rider position, and so on.

As an engineer, we loved to pass the cause off to sudden equipment failure, but ultimately, the engineer's design choices, proper maintenance, supervision, were much more likely. The machine's failure came as a result, rather than the cause.

Hi,

A spoke that breaks at the nipple is moreorless guaranteed to
jam into something and subsequently cause a serious crash.

You say the spoke was "gone". Ascertain how / why ?

rgds, sreten.

I've had a rear wheel spoke break and throw the wheel immediately out of true far enough that I suspect that had it been on the front wheel I'd likely have gone down.

Is the question whether a single spoke failure can cause an endo, or whether it was the likely cause of one in the particular case?

If the second, the evidence exists to answer the question. If you draw a free body diagram of the bike and rider, properly estimating the center of gravity, you can readily calculate how much braking force would be required to lift the rear wheel and start an endo. Once started the geometry changes making a full endo the outcome unless the braking force is reduced (not likely with a jammed wheel).

Without any data, I'll offer a crap shoot estimate that the required braking force would be someplace near 3/4s of the riders weight (depends on his riding posture). Once you have an estimate of the force needed, then the jammed wheel can be torqued to see if it is jammed tight enough to generate the required force or would turn.

All this assumes that we have a correct sequence of events. It's also possible that the crash (for whatever reason) caused the broken spoke. Something that would be more plausible if the evidence shows that the spoke couldn't have caused the crash.

This specific crash aside, the idea of crash due to spoke failure is worthy of further research. Starting with a general value for the force needed to cause an endo, the next step would be to determine how warped a wheel would have to be to bind enough to generate that force (on dry pavement), then finally, cut a spoke in a variety of wheels to see if they warp enough to be the issue.

Maybe Airburst, can write a proposal for a project and do it using her school's facilities.

If it turns out that a single spoke failure can cause an endo, it's worth considering whether this is an acceptable risk, and for who.

Very true words in this post.

I once had a squirrel run underneath my bike at an angle.
His angle of entry combined with my speed caused me to roll over his tail with my back wheel at a very narrow angle.
The narrow tire immediately rolled off the side of the squirrels round tail causing the back wheel to step sideways a few inches.
I am convinced that if I had not been paying attention that this incident could have been a lot worse than it was.
Thankfully in this case I did not go down, but it surely had me slowing down.

Wise words spoken by FB here...

Well, in my world they rate high enough since my son-in-law and son both had squirrel caused crashes.

My son-in-law had a squirrel run through a low spoke count front wheel (16 radial bladed spokes) that caused an immediate crash. He suffered a fair bit of road rash and an injured hand. The fate of the squirrel was not recorded in detail but the term "Cuisinart" was mentioned. So, after that we were sure the low spoke count was a major contributor.

However, about a year later my son also had a squirrel go through his front wheel and this time it was a 32 spoke, 3X very standard wheel. The resulting crash was at lower speed and the damage to my son was minor. Again, the fate of the squirrel was not recorded.

Conclusion: a higher spoke count isn't adequate protection.

Back in the we had a customer who woke up the ICU with no clue as to how he got there. He only rembers riding down a back country road. All his tests were negative and he was really freaking out because nobody could figure out why he blacked out and crashed.

I said, "Larry, relax, your fine." To which he replied, "what do mean, the docs couldnt find anything?" "I found this in your front wheel," and handed him a big chunk of rabbit fur.

so the simple answer is yes, anything type of front wheel issue, broken spoke, flat tire, a stick on the spokes or a wild animal running into your wheel could as cause an 'endo'

This is the first time I've heard of a squirrel jumping into and getting caught in a 32s wheel. It's far more common with low spoke counts.

Years ago I had a squirrel incident, where he was crossing the street and a passing car made him reverse direction right into my front wheel. He pinged off the spokes, so there was no consequence, except that I'm more squirrel aware these days. It might be that my higher speed saved me from a worse fate, or it might have been luck.

I theorize that the length of time that the gap is open between spokes is a key factor. at higher speeds, and with more spokes the time between spokes short enough that things are pinged back before they can get far enough to jam. If I'm right, it doesn't mean that wheels are immune to things jamming, just less likely.

This guy rode a Miyata 1000 (IIRC) so it was probably a 36 hole wheel, the fur was caught up in the outermost spoke cross. His made it through with just a little road rash, his helmet was broken into pieces (an early Giro with the lycra style cover)

how low is low spoke count?

If there is one thing that this thread has taught me, its that we need to eradicate those horrible squirrels that only seem to be causing major bike accidents and resulting bicycle spontaneous combustion.

Think of the bicyclists, nuke all squirrels!

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I can crash without any mechanical failure whatsoever on my bicycle.

I thought the whole idea of tying and soldering the spokes on a wheel build for a track bike
was essentially to prevent the possibility of a broken spoke flopping around and possibly locking
up a wheel, so I'm gonna go with "could have been the cause, or could have been a result of the crash".

Because I've managed to crash and break one spoke in a rear wheel as a result, too.

There's no magic cutoff between "conventional" wheels and low spoke count wheels. However traditional front wheels use 28, 32 or 36 spokes, and the more recent "low spoke count" front wheels range from 16-24 spokes. There might be front wheels with fewer spokes, but I don't know of any offhand. So 20 or less would be low spoke count, 28or more is conventional, and 24 is a matter of opinion.

A partially broken spoke can cause spectacular things to happen if it were to get wedged against the fork. The telltale indicators of such an accident would be gouges/scratches on the back of the fork where the spoke would have to have jammed.

Ordinarily, a broken spoke will pull a wheel out of true, and it would be like you hit the brakes with moderate pressure. Given the lack of clamping force from the opposite caliper, there's really no way you could rub a brake pad hard enough to endo. Something else is needed to stop the wheel that quickly. If an inspection of the fork turns up damage on either the back or inside of the fork, its a possibility something jammed the wheel.

I'd bet money that something else caused the crash, and the broken spoke is a result of the crash not the cause.

I speculate that a way to mitigate a chance of a crash due to anything being caught in the spokes is to use a dish wheel, no spokes.

You'll notice that even when using disc rear wheels for time trials, riders still use spoked front wheels. That's because side winds on disc wheels make steering control very difficult, if not almost impossible.

I think anything under 28 is low.

I just looked at bike with at least 3 cracks in the deep section rim at the spoke holes.....only 12 spokes per wheel will do that!!!

If a squirrel runs into your 32 spoke front wheel when you're going 20 mph is it less likely to find a gap to get caught in than if you're traveling at 10 mph? Or, does this also depend on the speed of the squirrel? I'll wager squirrel velocity has more to do with this than might meet the eye.