I’ve got Hope M4 (gold type) brakes on my bike. They’re IS as are my forks (pikes) and i’ve been running a 180mm rotor with no adaptor, this has been fine. This afternoon I’ve fitted a 203mm rotor and a IS to IS + 20mm adaptor. The rotor is a saw type M4 one.

The issue is that at first the rotor was actually hitting the caliper (where the hole for the rotor ends), a bit of fiddling sorted this out with pretty limited clearance. Now it’s rubbing very badly on the pad that is on the fork side, it pretty much rests against it, not stopping the wheel from spinning but definitely slowing it. I’ve been riding DH on it this afternoon and it’s usable but I’d like to fix it before riding XC! Anything that i’m doing wrong or that I can do about this?

Cheers for any help!

IS caliper needs a 200mm rotor, not 203mm. What kind of “fiddling” have you been up to?

Pad rubbing is down to alignment, stuck pistons or air in the system. Given that the problem didn’t exist before you up-sized the rotor, I’d suppose that alignment (and too big a rotor) is the cause.

Are you sure that your adapter is the correct size? I’m only really aware of adapters being for specific sized rotors (i.e. I’d be looking for an adapter for a 203mm rotor), but since I don’t really understand geometry and suchlike it’s probably perfectly posible to make a +20mm adapter to extend a current one. However since adapters seem to need to be front or rear specific might this also be the case for you +20mm one, could you have got this mixed up?

Everything said makes sense, it’s entirely possible that I’ve got myself mixed up, I should have another adaptor coming this week (I bought one for front and one for rear without thinking if they were end specific) so I’ll try that one. I didn’t that a +20mm adaptor would probably need a 200mm rotor, didn’t even consider that! Might do a bit of bodging or just refit the 180 whenever I want to ride XC.

There is no adaptor for fitting a 203mm rotor with an IS Mono caliper. You need to make sure that using the 203mm rotor isn’t causing strange pad wear – like where parts of the pads don’t get worn and would eventually meet, causing the brake to fail.

OK thanks for the info, I’ll see if I can find somebody who fancies swapping with me!