Scratching my brain on this so didn’t know if anyone can help?
A friend of mine recently came off his bicycle after hitting a pothole (Very common in the UK) and ever since he seems to have had an issue with the bike leaning to one side (Drive side) when he rides no handed.
I have put the frame on a surface plate and the seat tube and BB seem to be at 90deg to each other. The headtube was slightly off by 0.5Deg and the frame looks to be straight using the appropriate Park Tools checker. Forks look straight and the wheels true.
I would be interested in people’s thoughts on this. Is there anything else I should check? He says that when he rides normally it doesn’t feel odd or misaligned. Any ideas?
Is it carbon or steel or aluminum? If carbon, good luck. Nothing against carbon just that I don’t have any expertise there.
Measure the fork for side to side bend. A low tech way to do this is stick a straight broom handle through the steerer tube to the axle and measure each side of the handle to the inside face of the dropouts. The tighter the broom handle is in the steerer and the straighter it is the better (obviously!). Rotate the handle 180* and measure again. All of the measures should average out to within a mm or so.
If you have a v-block and surface plate, then use that. set the blades so they are perpendicular to the plate and measure the lower dropout distance from the plate, rotate it 180* and measure the lower dropout from the plate. They should be the same.
Beyond that is it possible the front wheel was just cocked in the fork after hitting the hole? Re-install correctly and see if that fixes it.
One of those engineering maxims: If it’s acting different yet nothing measures as unusual, then you’re measuring the wrong things. A few things easy to check:
ST coplanar with HT. Can be done by eyeball from the front of the bike.
Rear wheel vertically aligned with the ST and tire centered between the chainstays.
Fork (and this is where I’m suspicious your problem lies): As others have mentioned, there are some low-tech ways to do it, but best if you can set it up on a surface plate or in a lathe (lathe chuck holding the steerer) to make sure the blades are equidistant from the center line. Also make sure the steerer’s not bent. Eyeball the front wheel: is it lined up with the rest of the bike?
If the bike is pulling to one side noticeably, you’re probably looking for a misalignment of at least a few mm. It should not be hard to find.