# Brake shoe - coefficient of friction & Area

• k.udhay
Additionally, a wider shoe will create more drag which could affect vehicle performance in a negative way.f

#### k.udhay

Hi,

Will I have a higher slipping force / torque by increasing the width of my brake shoe and drum? Though my instinct says it is possible, textbook says it's only the coefficient of friction that controls the slipping force. Can you pl help me understanding this? Thanks.

The friction force is determined by the coefficient of friction and how hard the brake shoe is pressed against the drum. A brake shoe with larger area squeezing the drum with the same force will not give a larger friction force.

However, since the brake shoe has a larger area, there will be a smaller force per unit area on the brake shoe, so it will not wear out as quickly.

With a lot of material combinations the coefficient of friction is not constant and depends on the pressure. Often a reduction in pressure will increase the coefficient of friction.

Another separate effect is that, as mentioned, it will not wear out as quickly, so you could also use a different (softer) material to get a higher coefficient of friction with the same wear rate as previously.

With a wider drum there will be a greater area to dissipate heat, so peak temperatures will be lower.

Thank you all. Sorry for a late acknowledgment!

As said earlier, a wider shoe/drum will absorb and dissipate more heat. Heat affects the friction coefficient of the shoe. Depending on the material, an optimal temperature exists to get the peak friction coefficient. If it is too low or too high, the friction coefficient goes down and if its high enough it can go down to practically zero (brake fade).

Shoe compounds for street vehicles are usually of the 'cold' type, meaning they work well with relatively cold parts. Racing compounds are usually of the 'hot' type, because the brakes are always relatively hot due their frequent use. On the other end, racing compounds can have friction coefficient lower than street compound at lower temperatures. How to Choose the Best Street and Track Brake Pads

So with the same shoe compound, a wider shoe absorbs and dissipates more heat and thus will exhibit brake fade later.