Traction, traction force or tractive force is a force used to generate motion between a body and a tangential surface, through the use of either dry friction or shear force. It has important applications in vehicles, as in tractive effort.

Traction can also refer to the maximum tractive force between a body and a surface, as limited by available friction; when this is the case, traction is often expressed as the ratio of the maximum tractive force to the normal force and is termed the coefficient of traction (similar to coefficient of friction). It is the force which makes an object move over the surface by overcoming all the resisting forces like friction, normal loads (load acting on the tiers in negative Z axis), air resistance, rolling resistance, etc.

Traction can be defined as:

a physical process in which a tangential force is transmitted across an interface between two bodies through dry friction or an intervening fluid film resulting in motion, stoppage or the transmission of power.

— Mechanical Wear Fundamentals and Testing, Raymond George Bayer

In vehicle dynamics, tractive force is closely related to the terms tractive effort and drawbar pull, though all three terms have different definitions.

The coefficient of traction is defined as the usable force for traction divided by the weight on the running gear (wheels, tracks etc.) i.e.:
     usable traction = coefficient of traction × normal force.

Traction between two surfaces depends on several factors: