Traction Coefficient and Legal Regulations
The driving friction limits are essentially determined by the ratio of the static axle load of the driven axle to the total weight which is called the traction coefficient τ.

Eq. 3-49

Its value is proportional to the position of the center of gravity and hence most of all dependent on the engine position inside the vehicle and the load condition.
The figure shows a representative cross-section of vehicles for which the traction coefficients dependent on load condition for a front-wheel drive, standard-drive, and rear engine, rear-wheel drive (by law, the vehicle load is indicated in kg or in t) are indicated.
A front-driven vehicle has favorable traction conditions in unladen driving conditions since the engine is located above the driven axle. This however deteriorates with increasing pay-load since the trunk is positioned on the rear axle. In contrast, an improvement in the traction coefficient results when vehicles with standard drive are loaded such that the they balance out the conceptual advantages of front-wheel driven vehicles. Furthermore, the rear axle is additionally loaded by the dynamic shift of weight to the rear axle during acceleration or climbing. In passenger cars with rear-engine rear-wheel drive, the good traction coefficient changes only insignificantly when loaded.