Ask A Scientist© Engineering Archive

Index Key:   ENG034
Author:      dryden
Subject:     Breaking force of automobiles.
Does anyone know the average breaking force of an automobile?

Response #:  1 of 2
Author:      jade hawk
The general rule of thumb:  maximum longitudinal or transverse force is
about 1 g.

Response #:  2 of 2
Author:      dipper
Actually that is quite accurate.  It boils down to the coefficient of
friction between common tire rubber and the pavement which is about 0.92g
(average) breaking force and about 0.7g after it is sliding.
The equations get a little more difficult though, when you take into
consideration the interlocking surfaces of the common soft-rubber tire and
the rough surface of most pavements.  Width of the tire has no effect on


smooth surface coefficient of friction, but does have an effect on the
interlocking surface effects of the tire.  In effect, the softer the rubber,
and the rougher the surface, the higher the braking (or breaking) force. 
For example, some Formula one cars have braking forces that exceed 2.5 g's!