Brake Master Cylinder Bore Calculator

Inputs

Target line pressure (P_t)

Desired hydraulic line pressure.

bar

Pedal force (F_p)

Driver force at the brake pedal pad.

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.

Default result

Required bore(d_t)

22.2mm

Pass

Also computed

Current line pressure(P_c)52.69bar

Bore change−3.203mm

Master cylinder force(F_m)2,670N

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.