Brake Master Cylinder Bore Calculator
SI
Imp
Imperial
Inputs
View results
Target line pressure
(P_t)
Desired hydraulic line pressure.
psi
Pedal force
(F_p)
Driver force at the brake pedal pad.
lbf
Pedal ratio
(R_p)
Mechanical pedal leverage ratio.
Assist multiplier
(A)
Use 1 for manual brakes, or an equivalent booster assist multiplier when known.
Current bore
(d_c)
Existing master cylinder bore for comparison.
in
Results
Default result
Edit inputs
Required bore
(d_t)
0.8739
in
Pass
Also computed
Current line pressure
(P_c)
Pass
764.2
psi
Bore change
−0.1261
in
Master cylinder force
(F_m)
600.2
lbf
600.2 lbf
Method notes
2 notes
Smaller master bores raise pressure but increase pedal travel; larger bores reduce travel but require more pedal force.
Final brake sizing also needs caliper volume, pedal travel, bias, booster curve, fluid expansion and tire grip checks.
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