Disc Brake Torque, Pad Force, Pressure, and Thermal Energy

Disc brake design calculator

Connect pad friction and geometry to brake torque, vehicle deceleration, stopping energy, power, and a first-order rotor temperature rise.

Power during the ideal constant-torque stop

Power decreases linearly as wheel speed falls; the area under the line equals the energy dissipated by one brake.

How to use

Choose whether to solve for brake torque, normal force on each pad, or friction coefficient.
Enter the required brake inputs in the displayed units. “Force on each pad” is the normal force at one friction face; one opposed pad pair has two active faces.
Select uniform wear, uniform pressure, or manual mean radius. Enter the inner and outer swept-track radii, or a validated manual effective radius.
Enter one-pad area for mean pressure, then vehicle mass, initial speed, loaded wheel radius, and the number of equally loaded braked wheels.
Enter thermally active rotor mass, average specific heat, and the fraction of one brake’s energy entering its rotor.
Select Calculate to update the canonical result, vehicle metrics, thermal estimate, and power plot. Select Reset to restore the documented example.
Interpret torque, pad force, total clamp force, pressure, ideal deceleration, stopping energy, power, and temperature rise together. Verify tire grip, axle balance, hydraulic capacity, material limits, and component ratings independently.
Do not use this first-order model for brake certification, fade prediction, repeated-stop thermal history, transient conduction, ABS behavior, tire-force limits, or safety-critical sizing without a validated system model and test data.

Equations used

T = n_f μ F r_e

F = T/(n_f μ r_e), μ = T/(n_f F r_e)

F_clamp = n_f F, p = F/A

r_e,wear = (r_o + r_i)/2

r_e,pressure = (2/3)(r_o³ − r_i³)/(r_o² − r_i²)

F_b = n_bT/R_w, a = F_b/m_v, a_g = a/9.80665, t_s = v₀/a

E_k = m_vv₀²/2, E_b = E_k/n_b

P_avg = E_b/t_s, P_peak = Tv₀/R_w, ΔT = η_rE_b/(m_rc_p)

Symbols and units: T is torque per brake (N·m); n_f is active friction-face count; μ is the dimensionless effective kinetic friction coefficient; F is normal force on each pad (N); F_clamp is total clamp-force magnitude (N); r_i, r_o, and r_e are inner, outer, and effective pad radii converted from mm to m; A is one-pad area converted from cm² to m²; p is mean pad pressure calculated in Pa and displayed in MPa; n_b is the integer braked-wheel count; R_w is loaded wheel radius converted from mm to m; F_b is total ideal road braking force (N); m_v is vehicle mass (kg); v₀ is initial speed converted from km/h to m/s; a is ideal deceleration magnitude (m/s²); a_g is deceleration in standard gravity units using 9.80665 m/s²; t_s is ideal stopping time (s); E_k is vehicle translational kinetic energy (J); E_b is energy per brake (J); P_avg is average power per brake (W); P_peak is initial peak power per brake (W); η_r is the 0–1 rotor energy fraction; m_r is thermally active rotor mass (kg); c_p is average rotor specific heat (J/(kg·K)); ΔT is adiabatic rotor temperature rise (K, numerically equal to a °C increment).

Sign convention: positive input torque opposes forward wheel rotation; displayed force, deceleration magnitude, energy, power, pressure, and temperature rise are positive magnitudes.

Assumptions and limits: equal torque at all braked wheels, constant μ and torque, level straight-line motion, no drag/grade/rolling resistance/rotational inertia/tire slip/load transfer, and a lumped adiabatic rotor. The model does not predict fade, boiling, thermal gradients, convection, radiation, or repeated-stop accumulation.

References:Engineering ToolBox — Disk Brakes: Torque and Force; Engineers Edge — Disk Brake Design Equations.