If you took a rear 180mm IS rotor adaptor and fitted it to a set of IS mount forks, what size rotor would you need?

I’ve been sent a set of front and rear brakes with 203mm front and 180mm rear rotors, but the same adaptor with both brakes.

I don’t have the rest of the bike to check the mounts with, so wanted to check before I contact the seller.

Thanks.

200/203 on front – I reckon you’re OK (unless yr fork is a weird “bigger” IS, but that wouldn’t be the seller’s fault)

I use them interchangeably, though mfrs tend to sell as though they’re specific

Rear STD mount is 20mm smaller iirc, so just add 20

Cynic, you do rc.

So it’s a 200mm front mount rather than a 203mm mount?

I feel like I would want a 203mm mount for my 203mm rotor wouldn’t I?

It’s all Magura if that’s relevant.

My new forks are Post Mount rather than IS, so I do need a new mount whatever, but if the mount is for the wrong sized rotor, maybe I can get it swapped.

Sorry, logged in with my housemates account.

it’ll be OK – at the worst, a couple of thin washers’ll lift it enough but I doubt you’ll need it

Yeah, but I can’t use that mount anyway as the one I need is post-mount, so if I’m within my rights to ask for a proper mount it might be useful.

The adaptors are size specific, especially the 203mm as it’s also offset rather than just a spacer.

Contacted Leisure Lakes, who sold the brakes, they’re sending the correct rotor (Post Mount) adaptor out next week. 🙂

Top service!

Hope 183mm rear post caliper to IS mount is the same mount they list for 203mm front post calipr to IS mount.