why do wider slick tires gain more traction when surface area does not affect force of friction

Question

Explain why putting wider slick tires on your car improves traction if we dont see surface are in the equation. FF= meu×mass×gravity

Answer 1

The dependence on surface area is contained in the model for estimating the coefficient of friction μ.  The coefficient depends on the bodies in contact, not just on the materials they are made of.  The geometry of the bodies, such as contact surface area, affects μ.