Dual mastercylinder help

[Dutchie]

I need some help of the brake experts on this board. I want to go with a dual mastercylinder setup when i do my brake upgrade. In front i have 993TT Brembo,s for the rear i will use 993 brembo,s. The site of Bill Verburg is a great help in finding the parts you need btw !

Grady says you need to know your caliper piston diameters, pad area and effective pad radius. I think all the info is on Bill,s site allready but i don,t know how to calculate wich mastercylinders i need. Can someone help me calculate the sizes please ?


Tia,

[Bill Verburg]

As usual it depends

Assuming you are going to use 993tt/RS Big Reds(of whatever color) and 322x32mm rotors in front

and
assuming 30/34 n/a 993 rears(965 would be a bit eaier to fit) on 309x28mm 930 rotors, then you will probably want a little more rear bias in the twin master, unless there are some wacky wheel/tire /suspension items.

and assuming a pedal ratio of ~ 5.5 - 6:1

Twin master are generally sized at 50 -70% of tandem master because of the balance bar.

993 uses 23.8mm tandem m/c, 993RS uses 25.4mm tandem m/c, both boosted which has a large impact on the effectiveness of the brakes

So, I would start w/ twin 5/8", see how that feels, tweek w/ the balance bar and only if necessary put a bigger m/c on the end that you want to reduce bias at. Take small steps the m/c are cheap.

A bigger m/c will always reduce the amplification of the force provided by your leg

[Dutchie]

Once again great info Bill thanks ! i found someone here that has tilton mastercylinders that are 0.625 so they should work fine for a basic setup. I want to go without a booster for better feel or is that a bad idea ?

[Bill Verburg]

5/8" = .625"
With the bigger brakes I like boosting, but again it depends on a lot of other things as well. I don't know of any boosted twins any how.

feel is a combination of master/slave ratio, pedal ratio, pad friction and stiffness of all the parts involved, one way to get better feel is to reduce the master/slave ratio but that means you have to push harder for the same effect, everyones comfort level here is somewhat different, boost levels the comfort zone.