I was wondering whether 20" wheels can get away with smaller rotors than 28" wheels, and if there is a correlation, if it is linear. If it was linear, then 140mm discs on a 20" wheel would be equivalent to 200mm discs on a 28" wheel (and it would be unnecessary to mount anything bigger for pretty much any application).
At a given forward speed, the circular speed of the rotor scales up linearly with decreasing wheel size, which on smaller wheels should help with the cooling and should provide higher friction power and thus higher braking power.
But I can't find any source confirming this, so I'm asking here.