my commuter lives in the kitchen and last night i got it out to put some air in the tyres and noticed the rear wheel wouldnt turn properly. on closer inspection it turned out that the disc rotor had somehow warped…possibly due to something heavy leaning on it for a few days/ i took it off and tried to straighten it by hand and using some pliers/adj. spanner.
this morning i noticed its still warped and on pulling the lever can notice it when the brake lever starts to move back and forth due to the rotor pushing the pads back and forth in the caliper due to warped rotor.
any ingenious methods for straightening it out or should i just stick a new rotor on?

Not worth the effort IMHO, just stick a new one on Disco brakes

if it’s not folded, then it’s worth a go- new rotors won’t necessarily be straight either.

It’s hard to explain, but the best way to do it is in the bike. Take the caliper off, and cobble together brake adaptors so that you end up with a bolt threaded through one of them, pointing at the rotor. (on IS mount this is usually easy- undo one end from the frame/fork completely, slacken the other bolt so the adaptor moves, then swing it round til the unused bolthole is over the disc track.

You just made a precision runout gauge. By tightening/loosening the bolt, you can easily find high points in the rotor (either by eye, but I do it by contact), then true accordingly with an adjustable wrench. voila, it is straight. Unless it’s ****ed, in which case, it’s still ****ed.

It’s certainly possible, though I don’t do it quite to the level of detail Northwind does. I just leave it on the bike and use the brake calliper as a guide to where it’s rubbing then just attack it with an adjustable spanner. Worst case, I end up having to throw £15 on a new disc.

TBH I think it’s one of those things where what sounds like a hard way to do it on paper, is quicker to get decent results! I probably sound like a mad anal retentive but it doesn’t really take long

I’ve done it wheel in and just gradually going round spinning to hear where it catches the pad, small bit of adjustable spanner, spin to find next bit, adjust, etc.

Usually end up doing it after frustration that I can’t get the calliper to align without disc rub and decide it’s probably a warped disc. Likely I’m making things worse and I’ll end up with uneven pad wear, but at least it’s not making a noise 😀

I normally use my hands to straighten them, it doesn’t take much force. Just need a careful look at where the disk is warped and mark the area with a pencil.
Hard to completely true them IME but you can make substantial improvements.

Yeah as above, just use your hands.

the rotors are some lightweight tektro 160mm wavy ones. i took the rotor off last night and again tried to straighten it and used a table as a guide to see where the warped bits were. it seemed to me that it may in fact be coming from the rotor arms themselves.
i’ve tried all the other methods too but i like Northwinds method so i’ll give that a try next, but if all else fails then i do have some spare deore rotors that i might stick on instead

i did read somewhere that heating the rotor might straighten it…or is that just a bunch of old wives tales?

I’ve got one of these when one needs a bit of a tweak, seems to do the job.

http://www.sigmasport.co.uk/item/BBB/Disc-Straight-Disc-Brake-Truing-Spanner/JZ6?gclid=CL7IjoPsk8YCFUMUwwodSDYAaw

I use some chalk to mark the rubbing area. Spin the wheel and with a stick of chalk held against the fork or chain stay gradually move the chalk inwards. Then I use my hands – less chance of messing it up than with a tool.