I have just fitted set a brand new Shimano Saint 200mm disc and caliper to my KH29 unicycle. I notice that it touches (and makes a light noise) on about 1/4 of the disc as it rotates. Do I need to put a few miles on it to bed the new disc and pads in?
You can probably tweak the disc a little to prevent that - it depends how much it bothers you as it’s a bit of an art to get discs dead straight. I’d think it unlikely that bedding in will make much difference.
Actually I don’t even think this would work since the brakes are self adjusting. As the pads wear the pistons move further out of the cylinders, but only retreat the same measured amount as always. So, unless you have a seized piston, you should always have about the same clearance between the pads and the rotor.
I was thinking along the lines of my TRP’s that are not self adjusting, my bad.
Either way I’d just tweak the rotor. It’s a pain in the ass trying to get a caliper centered perfectly over a rotor with no rub without straightening the rotor a bit. I’ve yet to see one that was perfectly straight.
Thanks for the tips. I would imagine though that because the rotor is attached to the crank and there will be tolerances with the crank and hub that the crank might not be 100% at a right angle. This tiny fraction, would be exaggerated over the length of the rotor which makes the rotor not straight.
Unlikely it’s that, as the parts are CNC machined to very small tolerances, but its worth checking - mark on the rotor and on the crank where it is rubbing and try rotating the rotor on the crank. If it keeps rubbing in the same place on the rotor then you know the crank mounts are straight and the rotor is bent. If it keeps rubbing at the same point on the crank then the rotor is straight and the crank mounts not. If you’re really lucky they might both be a bit out and you’ll find an optimum point with no rub.
I’ve straightened rotors in a vice, but as I said it’s a bit of an art as you have to bend them past the point where they’re straight as they spring back.