Quote:
Originally Posted by Mark McM
What is it that you dislike about flat mount?
It is true that by definition it only accommodates 140mm/160mm rotors, but some frames/forks are built so that its flat mount will accommodate 160mm/180mm rotors.
The swap you did from 160mm to 180mm would have been just as easy with flat mount - for the front, you'd swap the orientation of the mounting plate, and for the rear you'd either insert or remove the mounting adapter (2 bolts on each).
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To fully air the grievances:
* Adjusting calipers is a major pain because the caliper fixing bolts must be accessed from the bottom. This is just so, so much easier on the post-mount calipers that you use with IS mounts, since the caliper bolts are accessed from the top. This is my biggest gripe.
* As you say, most FM frames can only accommodate 140/160. FM180 is extremely rare. Conversely, all rotor sizes are a snap for IS mounts.
* Carbon manufacturing tolerances being what they are in the bike industry, facing FM brake mounts is sometimes required on carbon frames - failure to do this can result in an inability to align the caliper.
* Flat mount is more difficult to implement on metal frames than IS, adding to frame construction costs. IS mounts are easily implemented by metal frame builders for both frames and forks in a variety of styles.
* Perhaps most subjectively, I think the aesthetics of IS are preferable for metal frames. Flat mount was invented to make carbon frames look more "tukt" and that's what it does. Metal bikes with flat mount often end up with wonky looking dropouts.
As for the question about actual IS mount calipers, as opposed to IS to PM adapted calipers, yes, those are an enormous pain due to the shims. Specifically my love is for IS mounts with PM adapters.