IMPERIAL
The torque required to slip the wheels is the vehicle weight over the driving tyres times the coefficient of friction of the driving tyres on rolling surface times the rolling radius of tyres divided by the overall gear reduction.
Where:
VW = Vehicle weight over driving tyres (lbs)
U = Coefficient of friction of tyres on average road surface, generally 0.6.
r = Rolling radius of loaded driving tyre in inches.
R = Overall gear reduction in both axle and transmission.
METRIC
The torque required to slip the wheels is the vehicle weight over the driving tyres times the coefficient of friction of the driving tyres on rolling surface times the rolling radius of tyres divided by the overall gear reduction.
Where:
VW = Vehicle weight over driving tyres (kg)
U = Coefficient of friction of tyres on average road surface, generally 0.6.
r = Rolling radius of loaded driving tyre in millimetres.
R = Overall gear reduction in both axle and transmission.