Originally Posted by
merlinextraligh
Road bike brakes should need higher capacity than MTB brakes.
Road bikes are travelling at higher speed, have less aerodynamic drag, and much less rolling resistance.
We've already seen that brakes that are acceptable performers for CX bikes can be problematic on road bikes.
I think you have that backwards. You are much more likely to encounter a situation where you need to limit speed on a steep descent for an extended period on a mountain bike. The worst case scenario for any braking system is a slow speed steep descent. That doesn't happen very often on a road bike. On a road bike you generally get to take advantage of wind resistance to dissipate most, if not all, of the potential energy loss while descending. Normal descents on a road bike involve mostly coasting with hard braking for corners. The coasting sections allow the brakes to cool.
Depending on the terrain and rider skill, it's much more likely you'll be descending slower on a mountain bike which means no help from wind resistance and less coasting.