I bought a belt driven bike which had had the rear triangle of the frame moderately bent (i.e. bent but no tubes collapsed or cracked) – it was a gamble as to whether it’s fixable…. It has a Nuvinci 330 hub with disc brakes which requires a large 135mm dropout spacing.
The frame is made of steel and I’ve been able to bend it to near alignment. However, as I don’t have a reference bike to compare measurements from, I’m struggling to figure out whether I’ve aligned it properly or not.
Firstly I aligned it based on the string test (Sheldon web page and also a Youtube video) so that the distance between the string and the seat tube frame member was equal both sides. I got this right to within 1mm and was happy with myself.
But then I dropped in the rear hub and tried to pedal it. It turned but it was making a noise which wasn’t very happy and you could tell the hub wasn’t aligned with the pedal wheel, with the belt rubbing as it seated itself on the gearwheels.
So then I bent the frame some more and now turning the pedals works really well and looks like it’s all fitting nicely, however if I do the string test there’s around a 6mm difference in the distance between the string and the frame between the two sides. However if I measure distance from each rear axle end to the same point on the headset it’s the same distance within measurement error, so I think the axle is sitting perpendicularly to the line of the frame.
So the question is this. Does all of the above mean my frame is bent in some way where I just won’t be able to fix it? The bottom bracket is one of those split types so that you can tension the belt – it looks horrifically weak structurally to my eye and it may well be that the bottom bracket axis is no longer perpendicular to the frame plane which I doubt I could fix. Or maybe a 6mm difference in the string test is not enough to worry about? Or are some frames deliberately made so that the string test should not return the same measurement which would mean that the way I have it now is perfect?
Thanks in advance for any help.
PS. I am waiting for a rim before I can restring the rear wheel and this is taking a while to arrive – hence I’ve not been able to ride it to see how it feels.