Shimano ICE tech rotors keep warping after truing
 

I have a Shimano Rt70 Rotor 160mm Centerlock Ice tech rotor in the rear and it had a small bend from new. I used the park tool straightening tool to get it trued to absolutely true, but after a ride with only a little breaking the exact same bend was back. I trued it again and after the same ride it was bent in the same place again. Does anyone still have any idea how I can get it to stay true? Thanks so much!

Do the brakes stop you? Do they make a lot of noise? Can you feel them dragging? Any other issues other than not the disc isn't quite centered all the time? It's perfectly okay for there not to be any visible gap between the rotor and one of the pads. IMO.

It isn't one of their better rotors, which I think have more inherent resistance to this.

Having said that, you might be able to ameliorate the problem by adjusting the caliper position.

It may be that the rotor has some built-in stress in the metal and every time it heats up from braking (not breaking, I hope) the stress gets relieved and the bend is restored. Try "over straightening" at the bend point and see if that works. Also, as was noted, if this bend is not causing problems with braking or noise, you can just ignore it.

From my experience in the auto industry brake rotors warp from heat and the thinner the rotor the easier it is to warp. If the disc is bending in the same place it is likely from a slightly undersized arm that does not tolerate the heat of braking. The cost of replacing the disc will be the expense of a test to see if it is a bad rotor. I would start there. Smiles, MH

many materials have a "memory" and will return to the bent state they were once in. Too bad they cant remember to be straight.

Replace with a new one.

-SP

Remove the disc and check the mounting surfaces on hub & disc are clean.

Barry

Thanks for all the tips do you think that it might help if I got the disk hot during a long decent and then tried to true it while it was still hot? Do you think that would make it more likely to keep it's shape?

I was thinking to stop as soon as the decent ends and just try to straighten it there. Theoretically would truing it while it was hot help with the "memory" of the disk?

Doubtful.

If it's rubbing and caliper adjustment doesn't make it stop rubbing, just buy a new (better) rotor. Or perhaps return the defective rotor, since you stated it was warped out-of-the-box.

Rear brake? Are you using mostly rear braking and overheating your rotor on every ride? Might explain why it's the rear and not the front.

I don't think I'm over heating them, I mostly do long XC rides and I only have a couple short descents on each ride. I just looked and it does seem to be getting a bit better every time I retrue it. Perhaps the warp will works it's way out.

What happens if you swap the front and rear rotors (assuming they are the same diameter)?

With mechanical avid bb7 discs, if you misadjust the pads, if the non moving pad is too far from the rotor, the moving pad can bend the rotor a bit
this could be your problem, or not at all I've experienced this from messing around with my bb7s when I first got them and was completely new to disc brakes.