Frictional forces can also be found between the tires and the surface of the ground. The presence of friction between our tires and the ground is absolutely necessary for motion.

Different tires and various riding terrain produce different coefficients of friction, µ. The difference between tires might be hard to distinguish but the variation between terrains is pretty easy to differentiate. Riding on the sidewalk is noticeably easier than riding among boulders! This is due to the greater amount of friction between the ground and the tires.