Coefficient of Traction is the ratio between the maximum amount of pull a machine can exert before slippage and the total weight on the machine's drive wheels or tracks.

• A. The ratio of maximum engine torque to wheel diameter
• B. The total weight of the machine
• C. The ratio between driving force and traction resistance
• D. The ratio between maximum pull before slippage and total weight on drive wheels or tracks

Answer: (D)

Traction is governed by friction between the drive tires or tracks and the surface. The maximum force the tires can apply before slipping equals the friction limit, which is the friction coefficient times the normal load (the weight on the drive wheels or tracks). So the coefficient of traction is simply the ratio of the maximum pull before slippage to the weight on the drive wheels or tracks. This directly captures how grip increases with more weight pressing the tires to the ground. The other descriptions don’t reflect that friction-limited pull relative to the normal load, so they don’t define traction in this context.