pwdeegan

so i've got 2008 avid bb7 roads, and the rear disc has warped (no idea why, the front rotor is fine; maybe because i locked up the rear wheel once or twice during my winter commuting). i've taken the rotor off and tried to straighten it using my rubber mallet, but without much success; the warp is about 2.5mm side to side---which is small enough to still use, but large enough to create constant (if still minor) rub on the pads.

1) any suggestions for straightening these things? mind you, my "garage" is my kitchen, and the cement patio outside is not level or trustworthy as a hammering surface.

2) i've also seen new rotors for sale that claim to "resist" warping. any experience with verifying this claim? these other rotors (e.g., avid "clean sweep") aren't any pricier than my current rotor (an avid "roundagon"). can i swap any 160mm rotor (the mounting looks identical)?

my bike is basically a glorified commuter and rando bike, but i do spend many afternoons trailering a 50# kiddie trailer (with kiddie inside), which places more of a burden on my brakes, but mostly on the pads (i would assume).

cbchess

I don't think hammering is the right approach. Try bending with an adjustable wrench. I made my own disc tool: cut a thin slot 2" to 3"in the end of a piece of wood, slide the wood over the disc, bend back to strait.

All of these approaches work best while the disc is mounted to your wheel.
***Make sure you clean your disc very well with rubbing alcohol after you or done or you will contaminate your brake pads.

Mondoman

Your extra load likely means your brake rotor is getting hotter under braking than it would otherwise, which can increase the chances of it warping.

silver_ghost

Park makes a rotor tuning tool specifically for bending back warped rotors (https://www.parktool.com/products/det...14&item=DT%2D2) but something like cbchess' DIY solution would work fine. It's easier to do with the wheel on the bike, that way you can use the brake pads as a reference. I've only ever done this in a repair stand, but find a way to hoist the wheel off the ground (if you turn the bike upside down you wont be able to see), spin the wheel and watch the rotor wobble back and forth between the pads. If you hold a peice of white paper behind the brake it's easier to make out which pad is rubbing when you hear the sound. The take you tool (DT-2, cresent wrench, whatever) and gently bend the rotor along the "arm" closest to the offending spot, if you bend in between the arms you run the risk of twisting the rotor, which is no good. It's easy to overcorrect, so start gently until you get a feel for how much force it takes to bend the rotor.

If none of this makes sense, I'm sure the Park Tool website has a much clearer explaination with pictures and everything. Good luck!

alcanoe

Yes, the Park tool works well and is more effective than an adjustable wrench. Truing rotors is just normal maintenance. You don't need a dial gauge. The brake pads make a good enough reference. I rotate the bike and adjust the height on the maintenance stand to get the best view of the disc between the pads.

Al

pwdeegan

very good info. thanks all.

any word on whether some disc designs actually resist warping more than others, as claimed by some manufacturers? or is any difference equivalent to different kinds of smoke being blown up my consumer-@55?

frankenmike 

I always just true the rotor on the bike, using my bare hands and the caliper as a gauge. Quite easy, actually. We have a park truing fork for this, but... well... what can I say?

pwdeegan

yeah, i just did the on-the-bike true with a protective piece of cardboard and my pliers---gently does it, and now it's perfect (or within .5mm of perfect, which is perfect enough!). i think a specialized tool (e.g., the park tool, or even the piece of slotted wood) is probably more effective over the long haul.

i saw a merchant selling a disc rotor that was made of steel with rotor arms made of aluminum---ostensibly for saving weight. i've got a feeling that this isn't a good idea in terms of longevity. but hey, if you've got the loot to pay 3x the price of a normal rotor for maybe a gram or two of weight-savings, then more power to you: support the economy, i say!