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Is the position of my calipers wrong? I've got 3-4mm of rotor on the inside perimeter of disc that the pads don't come into contact with and the 7-8mm strip that they do touch doesn't seem equivalent to the pad surface area. I would have thought the more surface the pads come into contact with the better but I've no washers under the callipers so can't adjust them to sit further over the disc. Is this a problem - should I file down the caliper adapters a bit, or is there something else I should do?
Do your pads overhang the outside edge of the rotor?
If so then you want to "lower" the caliper
If not, then you won't improve anything by moving them
Are you sure you have the right adaptor and it's the right way round ?
what size are the rotors and adaptors on the bike? I have been caught out before with the opposite running a 205mm disc when the adaptor was set up for a 203. Not thinking straight I used washers to fix the incompatibility until years later I spotted my mistake.
Maybe you have a 205mm adaptor setup and a 203mm rotor or something along those lines?
The rotor has to contact the whole of the pad. Otherwise, eventually the pads will close on the uncontacted part and the brakes will stop working.
Like enmac said the disc should cover the whole of the pad area, most likely is a miss match with the size of the rotor to the Caliper/mount. What brakes/rotors do you have and a pic would be quite helpful also?
I have clarks rotors which I think are 203mm but I'll check. The adaptors are generic ones for 203 that I'm using with slx callipers so that could be the issue. Perhaps shimano adapters would help?
Ok will be good to check as 203 on the back is pretty big, I guess first thing to do is check the actual rotor sizes and ensure you have the correct mounts. Maybe take some pics while you do it.
From my bike assembly history .... - was also hoping for the "perfect world".
But yes - tolerances stack up and the caliper might not "touching" the disc in a perfect manner.
And quite strange: no issues at all with brake performance and "some mismatch". Had max around 3 mm. Everything was fine.
If you find the "perfect adaptor". O.k. you are lucky. Then this is fine as well.