I am designing a frame and I want to use post-mount brakes (from mtb shimano line). I have issues finding exactly the dropout I'll use. I am wondering if it would be possible to use an adapter to install post-mount calipers (like the shimano SLX M7120) on a frame designed around a flat-mount dropout (like allotec C101-1, see image). Is there also constraints with disk rotor size compatiblity ? Ideally I'd want to be able to use 160mm or 180mm rotors.
Adaptors to use post-mount calipers on a flat mount frame are readily available from a variety of manufacturers. The only potential problem is that it might not be possible to site the caliper for large rotor sizes at the rear where the caliper is inside the rear triangle. You can design your frame to make it fit but you can see your plan will use alot more space than flat mount calipers the dropout is intended for.
An example: The Islabikes Janis was set up from the factory like this.
Note that using flat mount calipers on a post or I.S. frame is alot harder, specialist companies make these with caveats about potential frame fouling issues and incompatibility with certain calipers. This paragraph does not apply to you.
