Bit hard to describe this but bear with me.

Last year I had a fairly big crash on my bike, which is a Specialized Camber. I can’t recall the crash but nearing the end of my recovery when I was cleaning the bike I noticed I had bent the RH crank arm. http://singletrackworld.com/forum/topic/does-this-look-bent-to-you-1 I suspect what happened was my RH pedal caught a rock/root and threw me off, as I was on the CwmCarn red run so travelling a fair old pace and stopped pretty quickly.

Now, rather ashamedly, I went out for my first ride since the crash last weekend. All felt fine except for riding on some road sections between the trails. Whilst sat on the bike freewheeling it felt like the back of the bike was rocking (or swaying) from side to side, almost as if riding with a buckled wheel.

This was only very slight and I couldn’t notice off road, just on road. The wheel doesn’t seem to be buckled either (not significantly and I don’t have a jig) so any ideas what else it could be? I had a worrying thought I might have damaged the frame/knocked it out of alignment but this seems unlikely. Its got to be the wheel hasn’t it?

you can just hold a pencil on the frame against the rim and see if the rim is moving about at all. If it is do the same against the top of the tyre. Finally, check the tyre is seated properly.

Also check the wheel is sat in the dropouts and that QR/axle is tight.

borrow a wheel from a mate, if it still does weird things, its’ the frame… if not… it’s the wheel.

check the tyre is seated properly.

yup do that.

borrow a wheel from a mate, if it still does weird things, its’ the frame… if not… it’s the wheel.

Or, to be pedantic, it’s the wheel and tyre, so check the tyre for bulges.
A big rock strike can damage the casing without puncturing the tyre

I’ve had the same sensation as a result of loose spokes, didn’t look out of line at a standstill, but very noticeable when rolling.

Is everything attached/done up properly?

If yes then stand at the side of the bike, hold it by the bars with your hand on the brake.

Now put a foot on the pedal and put some sideways (and downwards, so it doesn’t just slide away from you) force into it.

Is anything moving? How much flex is there? Does the wheel hit the chainstay/seatstay? Is it the same from each side?

If you grab the back wheel and pull it from side to side does it move? Is there any clunking?

Check all the suspension pivots

Is your arse attached correctly?

Borrow a bike from a mate – if it still does weird things it’s you.

Cheers for the suggestions, some tinkering to do this weekend.

Arse still attached but post Christmas excess means the side to side motion may not strictly be bike related 8)

Could be the wheel bearings are going, or need the preload nipping up (depending on type).. grab the top of the wheel in the frame and see how much it moves side to side.

Check your spokes and cones. Big crash might have loosened cones and created a bit of play