Fitting a 203mm rotor

When fitting a 203mm rotor and caliper adapter I've seen people mentioning having to shim the caliper to get it to fit.

What is that all about? Would that be shimmed with specific washers or just some that were lying around?

I think they are referring to using a 203mm rotor in place of a 200mm rotor. The calipers will likely need to ve pushed out further to place the pads in the correct place over the disk.

If your previous rotor was concentric with the calliper then the 203 will be assuming you have the correct adaptor.

Two reasons
1.You shim where you have shims with the brake for the calliper side ie avids but not hopes.
2. Sometime people shim a 200 up to 203 with some appropriately sized washer – one needed iirc.

So a 203mm rotor and a 203mm IS adapter will require no shimming then.

Its usually normal to shim a caliper, but just for disc alignment within the pads. The shims are somewhat thinner than normal M5 washers, usually get them in packs of 0.25mm & 0.5mm for a couple of £'s. You wont know it needs shimming till its bolted up, you'll hear it/feel it rubbing on the pads.

it will require no shimming.
It wont rub in the pads the wheel wont turn as the caliper is clamped to the rotor… I did this with a 183 and a 180 rotor and avid brakes others should be fine though.
Not sure what rustler means as shims wont stop pads rubbing you need to properly align pads /calliper as per Hope instructions.

To repeat a 203 mm adapter wont need a shim for a 203 rotor

rustle is referring to IS calipers needing shims to move them sideways to center them on the rotor rather than nearer/further from the axle. Not needed with post mount with their slotted holes.