Traction refers to the friction between a drive member and the surface it moves upon, where the friction is used to provide motion.

For the purposes of driving a wheeled vehicle, high friction is generally desired, as it provides a more positive connection between the driving and driven members. In contrast, motion in a geared mechanism is provided by interference, and friction is usually detrimental because the gear mechanism has intrinsic sliding, and sliding under friction causes heating losses.

Traction between two surfaces usually depends on several factors including:

  • Material properties of each surface
  • Macroscopic and microscopic shape or “roughness”
  • Force of contact
  • Area of contact
  • Contaminants at the material boundary including lubricants and adhesives