Correlation between friction force and surface area

engineer888

As far as I know, friction force is equal to the product of the normal force and coefficient of friction, hence is independent of surface area.

So why is it that race cars have wider tyres than conventional vehicles?

davidm1732

The rubber compound is softer and stickier in racing tires (I'm in North America!), and can't handle the higher internal pressure that a street tire would, so to support the vehicle, you need to have a larger contact patch, and hence wider tires.

Take the surface contact patch area and multiply by the tire pressure to estimate the load it can support. PA = F

sgb27

Tyre/road friction is extremely complex, there are entire books on just this subject. Your formula is correct for a simple model, however what you may not realise is that the coefficient of friction will not usually be constant, even for the same materials at the same temperature. The coefficient of friction depends on the normal load, usually it is higher for lower loads. So when considering the entire vehicle it is beneficial to have a larger contact area (and a lower pressure between the tyre and road) to increase the coefficient of friction.

There may also be other benefits to wider tyres like reduced wear rates (allows you to use softer rubbers) and less overheating.