single circuit brake master cylinder sizing

[jessejazza]

I'd be grateful if someone could confirm the following.

I remember someone telling me that a 5/8 (0.625) cylinder gave more force to the brakes but along with more pedal movement (due to less fluid because of the diameter).

Where as if a 3/4 (0.75) is fitted there is less force but with less pedal movement. Basically it's a compromise (pressure = force/cross sectional area) and if a 3/4 is fitted like on Series Landrovers larger drums/discs are fitted to provide the requisite braking.

thanks

[welshpug]

yep, that's correct regarding the different pressures IF the leverage ratio is constant.

as for the larger drums/discs that's not always the case, it depends on the bore of the wheel cylinders or caliper pistons, larger diameter discs/drums typically just give higher leverage and a larger contact patch.

[jessejazza]

Thanks. I thought it was. I compared a 5/8 with a 3/4 on my 3 wheeler Rialto... and there seemed little difference in pedal travel. I've got too much pedal travel on this kit car which I've put a 3/4 on. I think Wilwood do 1" bore but I think i need to go back to a servo... trouble is, it leaves little room to get at the distributor.