Traction coefficient

The traction coefficient is the calculable physical quantity for determining the conversion of the existing drive force into acceleration .

This coefficient, commonly referred to as Tau , is, in simplified terms, the force that is required to move the load of the vehicle divided by the load of the vehicle. Specifically, the ratio of the possible acceleration in the direction of travel at the static friction limit to the acceleration due to gravity acting perpendicular to the road surface , i.e. a dimensionless quantity . When negotiating an incline, only part of the acceleration due to gravity acts perpendicular to the road, the other component acts against the direction of travel. A fully locked all-wheel drive achieves a coefficient of friction of τ = μ. The following applies to vehicles with uniaxial drive ${\displaystyle \tau }$

${\displaystyle \tau =q\,\mu }$

with the dynamic axle load share q ≤ 1 of the driven axle ( q = 1 corresponds to the wheelie ). For two-axle vehicles with wheelbase L , q results from the position of the vehicle's center of gravity

${\displaystyle q={\frac {d\pm h\mu }{L}}}$

Here d is the horizontal distance between the center of gravity and the non-driven axle and h is its height. "+" applies to rear-wheel drive, "-" applies to front-wheel drive, and vice versa when reversing. The term with h is small on black ice; then q is 0.5 with the same axle load at the front and rear.

A high share of the axle load on the driven axle is therefore advantageous for traction in wintry road conditions.

Individual evidence

1. ↑ friction Ing. Miroslav Petele publication of the project MICalc , accessed on August 1, 2013