Master cylinder bore sizes

[russtik]

I've just replaced my front brakes with HISpec 4 pot calipers. I have 2 x single master cylinders, one for the front and one for the rear. The front master cylinder is a Wilwood .625 bore which I suspect is faulty so I'm going to replace it.

I'm curious about the .700 bore for a more progressive feel. Has any here made this change?

[b33fy]

Loads of science behind master cylinder sizes with complex calculations required to get it right. Essentially the bigger the bore, more fluid is moved for the same pedal travel. What this does is shorten the travel and firm up the pedal, the downside is you need more effort. Go too far and the pedal feels solid and you have to exert considerable pressure to pull up. Go too small and there is less effort, but too much travel and a less firm pedal.

I use the suck it and see method, try the .7, logic says it should work with bigger caliper piston area than the two pots. if it’s no good, I’ll give you a tenner for it.

[steve m]

I am 99% sure my fronts are powered by a smaller bore cylinder than the back,
Ive never mastered the theory, so just gone along with what works

steve

[greenwoo]

Can't recall what i have on mine, i may have a .7or .75 MC that's brand new in the garage.
Do you have a bias valve so that you can fine tune?
I'd have a delve into the science& calculations if i were you Russ, you might find that with whatever pedal ration you have/calipers that you'd want to keep as is or maybe bigger than .7
With brakes there's so many variables, the biggest of which is how you like to feel them working....

[Rob E]

I wouldn’t worry russ, it’s not going to be driven is it ??