Ask A Scientist© Engineering Archive

Index Key:   ENG007
Author:      dryden
Subject:     Braking force of automobiles
Text:        Does anyone know the average braking force of an automobile?

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

Response #:  2 of 2
Author:      dipper
Text:        Actually that is quite accurate.  It boils down to the 
coefficient of friction between common tire rubber and the pavement which is 
about 0.92 g (average) braking force and about 0.7 g 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 force.  For example, some Formula One cars 
have braking forces that exceed 2.5 g's!