TwistedMinis
+1y
I can't tell you what specifically to get. Its kind of a preference thing, as far as pedal stiffness goes. But you still need to be able to move enough fluid safely to stop, but preferably without an impossible pedal. So this is the way I look at it.
Smaller bore, moves less fluid in its stroke but it is easier to compress the fluid. So you could use a shorter pedal. A larger bore moves more fluid, but the larger the bore the harder it will be to manually compress the brake fluid. But it will have a shorter stroke when moving the same amount of fluid. You would probably want a longer pedal.
Usually a 5/8" to 3/4" bore is pretty easy to move manually, and can move enough fluid to stop most light vehicles. Once you get up to 7/8", 1", and 1 1/8" it gets near impossible to press manually, and really should be a power system at that point.