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Accident post mortem.
I managed to get spat off the bike last week and and looking for possible reasons. I'm not in a current state to look around the bike as the broken shoulder and muscle damage on right leg is somewhat restricting.
Riding along at about 30km/h and the rear wheel locked up. this caused a slide which ultimately high sided and spat me off, I got back on and rode a further 1.5km. Nothing obviously broken on the bike. Rear mech intact, so not too sure if chain had jumped off the cassette. No potholes, no obstacles. It was an immediate and violent action from the bike (which makes me think that no stress was put on rear mech or hanger) and I'll give it a good look over when more mobile. No one else was involved.
Any thoughts of the cause in the meantime?
If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.
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43 comments
Bit late, perhaps, but I had something very similar cause by a loose rear skewer. I thought I'd tightened it enough but the resistance was due to friction in the (badly designed) cam, not clamping force. The wheel popped out soon after starting off out of the saddle, so I was spat (exactly that!) out over the bars. It was obvious what had happened looking at the wheel, but I reckon there's a chance the axle end could have popped back into the drop-out, in which case there'd be no obvious clue
Not too late at all. All possibilities welcome and good advice to check and double check th QRs before leaving home.
That's it, nothing else.
Here's the only damage I can find on the bike. Not much to show for coming off at 30-35km/h
Fulcrum are a nightmare, in that I guess they use different freehubs. Mine was sealed so I couldn't attack the pawls.
The Zonda, which is the same as some Fulcum (there's a surprise) has removable freebub. The spring a) isn't going anywhere as it should be hooked in and b) should probably be replaced (Ebay), so flying off isn't a problem. Pawls and/or complete freehubs should be available there too.
Measure the bearings an google the measurements to find cheaper bearings.
Watch videos, and prepared to take 10x longer, hit bearings 10x harder and skin knuckles more than pro mechanic.
Get a decent bearing press.
If the wheel is spare and doing nothing, what've you got yo lose by having a look.
I fear this is a bit of a tangent.
Thanks. I'll go for it!
After stripping the freehub down and replacing the bearings, and no obvious faults in the wheel bearings, I now hopefully have a fully functioning rear wheel which will be put to the test on the rollers this evening.
Here's looking at another few 100 thousand kms before the next freak accident.
That's sounding like some road debris (branch?) got caught up in your wheel, then. Good luck with the riding.
100% certain it's not that. No broken spokes, no bent spokes and no scratches or marks on the dust dirt that's accumulated on the spokes. No noise at the time of the accident. The only thing I'm currently more certain about is that this tory govt is corrupt.
What kind of brakes? Is it possible the rear brake locked up hard?
Absolutely no chance of that.
My money is on the hub.
I've had something similar with a failed freehub, but thankfully didn't get spat off.
It only started to happen when the speed picked up, the pawls were not allowing the freehub to spin when I eased off the power on the cranks (it didn't completely not spin, but there was significant drag). This caused the upper part of the chain to go slack between the cassette and front mech. It felt a bit weird, I looked down and saw the chain slopped on the chain stay and dangerously close to the rear wheel spokes.
It's possible you had something similar, but were unlucky enough that the chain jammed the rear wheel. Hope you heal quickly.
Cheers, I'll see if I can have a play with it on the workstand when I get two fully functioning arms. Not sure I'll be able to replicate that, but it might highlight something.
If you get the back wheel spinning up fast with the cranks on the stand, then stop the cranks you should see the chain droop if this is the problem.
It was a weird one to fault find as it wouldn't happen when I was coasting at my usual pace, only when I'd got some speed up and stopped pedalling. Freehub still worked, but there was just that bit of drag that was enough to cause the chain to go slack.
I wasn't going particularly fast at the time, but another unexplained failure of a similar style sounds like the way forward. Again, I'm trying to get my head around the physical side of what happened, and why. It'll be another week or so before I can get the bike on the stand. And a fair bit away from stripping the rear hub and there's no local independent shops in town (walking distance) to get the wheel to.
Muchas gracias!
Like everyone else I'm struggling for things that only would have caused it once and then everything is ok again.
just coz it's not yet been mentioned check the plates on every chain link. My nearest experience to what you describe is a chain plate flaring out and jamming the drive train and pretzeling the mech hanger. Definitely didn't manage even 1.5 meters after that happened though!
A cursory look at the chain, looking for scratches and contact on the chain, would indicate that the chain is fine. I didn't spin the cranks for a full look, but at the moment I'd say all fine.
I've had the ripped mech enough times to see damage a dodgy link can do. Again the jamming of the chain and the mech staying intact seems a bit odd.
I can only think you picked up something that jammed between wheel and frame. I have seen it happen with a dropped bidon. One in a million event?
Wishing you a swift and complete recovery.
Possible, but I don't recall seeing anything on the path to obstruct, nor anything odd when I picked myself up. But entirely possible, cheers.
I managed to get a 20mil wide, 150mil long bolt picked up by my back tyre and clonk the stays before I could stop. I wasn't going fast and was scanning but just didn't see it. However it didn't cause a jam, only a puncture as the threads pierced the tyre.
Whatever did happen probably got shook "loose' with the resulting crash so unfortunately I don't think you will get to the bottom of this.
You're probaly right. But it is an interesting exercise, imo. I won't get a much clearer idea until I get a good look at the bike, which is a good couple of weeks away.
Did the cranks also lock?
I hadn't thought of cranks locking. It's possible, but I rode it immediately afterwards. Pedalling stopped as it locked up.
Do we have experience of cranks locking up?
If the cranks locked up, that shouldn't cause the rear wheel to lock up as well.
I haven't had a good look at the tyre for a flatspot. But I'm sure it's rear locking up that caused the highside. Thinking now, it's probably the sudden cessation of pedalling that buggered the leg, and not being clipped in as I went A over T.
Good to see you back on here but not so good that you're a bit busted up. Heal fast.
Strange that you could pedal normally afterwards but, without any sign of something external jamming the wheel or drivetrain, I'd suggest the freehub is a distinct possibility.
Cheers.
I'm trying to get my head around the physics of a jamming freehub. It would jam to the wheel, which would continue turning, no? It would become a fixed wheel and force me to pedal. Or, if the freehub broke loose, I'd continue pedalling with no drive, no?
Me too. A freehub failure is more likely to that the pawls fail to engage so pedals spin freely without the wheel moving.
However, from what you've written you seem to have discounted external factors (jammed spokes, stuck chain) and the pedal jamming just prompted me to think of the hub. Very odd that there seem to be no obvious clues and it was subsequently rideable.
This is the bit that I find most perplexing.
I doesn't appear that anyone has had such a spectacular failure where the bike remains undamaged either. Which would give some sort of solace. I would expect a broken mech hanger to be minimum damge for these symptoms.
I'll try and get some pictures of if when I'm more mobile and flexible.
but the reverse is true, if the rear wheel locks, the cranks will no longer turn.
Definately sounds like something got stuck and stopped the wheel. I'd have a look for any damaged spokes, and also any sign of damage to the back of the seat stays and top of the chain stays.
Sounds a lot like when my mech hanger broke, and the rear mech tangles with the wheel and frame, locking up the wheel instantly when I had been doing 30kmh. Just a big straight line skid for me, no crash, but broken bike meant I had to finish on foot.
In the absense of any sign of foregin object intereference, I would then be looking at the bearings, but as you rode home afterwards, that seems less likely
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