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Discussion Starter · #1 ·
Hi

I crashed on a root on a slight downhill section at one of the local xc races and landed badly, think my upper body landed on the wheel a little.

My question is a hard one as I have no pics and you guys weren't there. Anyway what forces the qr to bend but not the wheel and hub as everything is fine apart from the front qr. Are they designed to bend like hangers? I'm just wandering if I've done any other damage and trying to understand how JUST the qr can be broken and nothing else...sounds too good to be true.

Any thoughts
 

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This is a tough one to...

explain without a bunch of high powered math. But basically it boils down to your fork flexed lateraly enough to cause the QR to bend. I.e. one leg flexed forward the other flexed back due to force placed on it during the crash. Most people find this hard to believe as forks usually (with a few exceptions) feel stiff an stable while riding. However even the beefiest forks flex to some extent, just like all bike frames flex. If they didn't they would break. The key in designing a perceptably flex free fork or frame is to engineer the way it flexes and limit that flex to a given threshold. In your case the crash exerted forces on the fork that surpassed the threshold and a caused the fork to flex in a sort of twisting motion. This allowed the fork to obsorb the force of the crash without causing damage to the fork. However that same twisting motion likely was well beyond the capabilities of the QR to handle, you can only make a shinny 5mm skewer so stiff. Hubs don't flex, at least not under any amount of force that would leave you consious and uninjured. And usually if you apply enough force to flex a hub it breaks or cracks and there is severe damage to other components. A hub will survive forces with little or no damage that will destroy a frame or fork.

With all that said, I would advise you to have the hub looked at, esspcially the load bearing portions, i.e. the bearings and axel. If you hammered it hard enough to bend the skewer you may have also bent the axel slightly and/or done damage to the bearings. Either could dramatically shorten the life of the hub. Have it looked at by a competent mechanic (tell em what happened) or if you are into it, do it yourself. As a minimum I'd disassemble the hub, check the axel for true and replace the bearings as you've likely flat spoted some of them. I would also recommend a careful examination of the fork, paying particular attention to the drop outs.

Good Dirt
 

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It would also help to know which version of the XTR wheel and to indicate where the QR bent. The 975 series XTR front wheels use a huge 14mm aluminium axle with a 9 or 10mm diameter bore down the middle (eyeballing mine, the bore is a couple of mm's bigger on each side of the 5mm Allen flats on the end caps), so that leaves some room to kink a 5mm QR axle if it gets tweaked enough.

The older 965 XTR wheels used a 10mm diameter axle so you may have bent the axle if it bent the QR.
 

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Discussion Starter · #5 ·
Thanks really helpfully. It's a Chris King qr front hub and a 05 Talas rlc 130. I'll check the fork and hub but to be honest I have no tools apart from my eyes and so far it looks fine but I suppose with the correct tools I wouldn't be surprised if the hub axle and fork were ever so slightly out.

Squash sounds like you were there when I crashed, your description sounds spot on in terms of directional forces which I couldn't get my head around. :)

I hate damaging pretty expensive parts. I suppose a way not to worry about these things is how free-riders and downhillers treat their machines and how much abuse their bikes take. Point is their bikes are designed to take hits better but like-wise our xc bikes do the same but just a lower threshold.

I'll mention it to the lbs and explain where to check for misalignment next time I get the bike checked.
 
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