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Disk and Shoe Brake Equations and Calculators

Disc Brake Calculator
A sectional view of a generic disc brake with calipers is illustrated right. 
Calculate Brake Torque Capacity Input       
Clamping force,  F = lbf
Coefficient of friction,  μ = -
Caliper mean radius,  Rd = in
Number of calipers,  N = -    
Braking torque,  T = 2*μ*F*N*Rm
Shoe Brake Calculator
 Stopping capacity is proportional to the normal force of brake shoe against the drum and coefficient of friction.
Calculate Brake Torque Capacity Input       
Coefficient of friction,  f =
Brake shoe face width,  w = in
Drum internal radius,  Rd = in
Shoe mean radius,  Rs = in
Shoe heel angle,  A1 = degrees
Shoe angle,  A2 = degrees
Shoe mean angle,  Am = degrees
Right shoe maximum shoe pressure,  Pmr = lbf/in^2
Left shoe maximum shoe pressure,  Pml = 150 lbf/in^2
C = in    
X = (Rd - Rd*Cos(A2)) - (Rs/2)*Sin^2(A2))
X =
Right shoe friction moment,  Mr = ((f*Pm*w*Rd)/(Sin(Am))*(X)
Mr = in-lbf
Y =  (0.5*A2) - (0.25*Sin(2*A2))
Y =
Right normal forces moment,  Mn = ((Pm*w*Rd*Rs)/(Sin(Am))*(Y)
Mn = in-lbf
Brake cylinder force,  P = (Mn - Mr) / C
Answer:  P = lbf
Z = ((Cos(A1)-Cos(A2)) / Sin(Am)
Z =
Right shoe brake torque capacity,  Tr = f*Pm*w*Rd^2*(Z)
Tr = in-lbf