I have just upgraded my front rotor to 203mm and cant seem to get the rotor to stop rubbing on the pads. I have had a look on the shimano website and cant see anywhere it says the max rotor size – any ideas?

is a 203mm rotor thicker than a 180 one – I didn't think so?

Is the rotor warped already? rotor diameter wont matter at all, and as far as I know all discs are the same width… Is it possible you have a 203 rotor and a 200 adaptor and its rubbing on the outside? Even then 1.5mm usually doesnt matter, but if it is that you can put a washer under each post mount to space it.

me either! but now im not so sure I dont have a pair of calipers to measure the thickness so hoping someone on here might know!

Another possibility is the ammount of oil in the system, I have heard of some brakes that hold the pads onto the disk if the reservoir is overfilled, not sure that happens with Shimano brakes mind you, is swapping the rotor the only thing you have done different?

Yeh obviously changed the mounting bracket for the caliper and re-adjusted it but thats all

cant see it being option 2 then, you sure about the adaptor you got? is it definately a 203 and not a 200?

both pads rubbing or 1?

Yeh def 203 – ill take it all apart again and double check everything and re do the adjustment

Rest assured all disks are the same width, ive mixed and matched brands many times with no issues, thats how comes some disk makers THAT dont actually make brakes and their rotors are universal. It must lie elswhere your problem.

Sticky pistons?
Check alignment of the caliper / mount and make sure the pads are parallel to the disc surface, not angled.

Rest assured all disks are the same width, ive mixed and matched brands many times with no issues, thats how comes some disk makers dont actually make brakes and their rotors are universal. It must lie elswhere your problem.

As long as that is the issue then I am sure it is something fairly simple. Just thought that they may be thicker for some reason

How old was the rotor you removed? Might just be possible that the pads/pistons had adjusted for rotor wear? I've had rotors wear to the point where there is a visible step between the braking surface and the arms.

Could try just pushing the pistons back in?

My LX frequently will rub the pads, and it gets worse the dirtier they get. A thickness of a few grains of dirt or sand is enough to set them off. Frequent cleaning and lubing the pistons and seals seems the only solution I've found. 😐 Perhaps it is related to the amount of fluid, I've not tried removing any. Perhaps I'll take a few drops out and see if it helps.

The other thing which can help my LX is occasionally re-seating the wheels. They move minutely within the drop-outs after a few days or weeks of riding, and with very small pad clearances that tiny offset can be enough to set them off rubbing also. Usually they touch only so lightly that they set the disks ringing, with a very high pitch that goes right through me. Irritating, but re-seating the wheels sometimes stops that one.

I've got LX brakes and rub every now and then is an issue, clearance seems really tight. My rear brake is usually fine but if I ever take the front wheel out I usually end up having to readjust the caliper as I get rub when the wheel is back it (slightly different tension of the QR perhaps). You could try pushing the pistons back in.

Did you touch the rotor surface fitting it? Again a bit of grease or even water (my LXs can sound rough if they get splashed) so cleaning the rotor may help.

I'm fairly new to disc but would the pads need re-bedding to the new rotor?

are you sure it's the pads? I swapped a Shimano for a Hope rotor and got terrible rubbing, I thought, till I realised the disk was ~1mm bigger and touching the caliper body 🙁

OK got it sorted now. Took some minute adjustment rather than the normal method of holding on the brake and doing the caliper bolts up. Like you say the clearance is tiny. Still a very tiny rub but after a ride or two I think that should hopefully wear off. I have to remove the wheel everytime to store the bike so hopefully when I put the wheel back on it should line up ok again!