hi
i have a 5/8 MC (1.3 stroke) and i would like to know wich caliper piston bore size i should go for (calipers are 4 pots)
i have the choice between:1" ,1.25" ,1.38" and 1.50" bore size
merci

There are other variables to consider such as disc diameter, tyre diameter, pedal length, pedal lever, size of the other end components (rear)

Fred Puhns Brake handbook runs through it all.

Do some basic calcs on a 5/8" bore with a 1.3" stroke on the various sizes of 4 pots and work out how much the pads will move.......... On my car full MC depression only gives 0.008" pad movement. This scared me but AP racing assured me it was OK and it does work fine.

My guess would be 1.25" 4 pots.

merci!