Jamar Performance Economy 13" Reverse Swinging Dual Brake And Clutch Master Cylinder Pedal Assembly

When selecting master cylinders, you'll notice with a smaller bore, you get more pressure but less volume. With a larger bore you get less pressure but more volume. You need to make sure that you have enough volume to supply your brake calipers, but at the same time, enough pressure.

For the tandem brake master cylinder pedal, offroad trucks and buggies will have more bias to the rear brakes. 60% rear and 40% front is a common starting point, with a lot of offroad racing vehicles ending up at 30% front and 70% rear. Opposite of a street vehicle.

A 5/8" clutch master cylinder gives you a softer pedal feel but you have to push the clutch pedal further down. The clutch pedal will move about the same distance as a stock beetle clutch pedal if you use a 5/8" master cylinder. A 3/4" clutch master cylinder gives you a harder pedal feel but you don't push the clutch pedal down as far as the 5/8" master cylinder because you're moving more fluid volume. The 11/16", for most people, is a happy medium.

For the single clutch master cylinder pedal, here is an example of the math. Pushing the clutch pedal with 100 pounds of force, a 6.43:1 pedal ratio and a single 11/16" bore master cylinder:

Pedal force at master cylinder:
100 lbs x 6.43 ratio = 643 lbs

11/16" master cylinder area:
A = π r²
A = 3.14159 x 0.34375 x 0.34375
A = 0.3712 in²

Line pressure:
643 lbs ÷ 0.3712 in² ≈ 1732 PSI

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