How Tires Work


Just was thinking this while my car was getting serviced.. Why do regular vehicles have tread which gets less responsive as it loses it’s tread, while race cars use slick tires for maximum grip? Wouldn’t physics say more tire on road = more surface to grip? If so, why do our cars even have tread? Is it simply to save on MPG? If so, are tires with worn thread less responsive?

In: 3

On flat dry surfaces it is true that more rubber contact means more grip, which is why racing cars often use slick tyres. However if you are driving through a water puddle, on gravel, on snow, etc. you need some treads. You need somewhere for the water to flow to as you drive over it or it will just stay as a layer between the rubber and the road reducing grip to almost nothing. The treads is there so the water can flow into them as you drive over it so you get more rubber on the road. On gravel the top surface is very lose and bumpy so you need the rubber to wrap around all the pebbles gripping them. So the treads is there to allow the rubber to expand into so it can grip the pebbles. Snow and mud is a combination where the tread both allow the rubber to get deeper into it where the ground is firmer but also allow it to throw the snow or mud back to propell the car forwards.

If you look at the racing cars with slick tyres they will change to wet tyres with treads when it starts to rain as these have much more grip. And any sort of off road racing or even just gravel racing is done on tyres with deep treads.

The tires on the average consumer vehicle are designed to last between 30-50k miles, race tires are designed to last maybe one or two thousand miles. The tread on normal tires is meant to deal with a wide variety of conditions, whereas racing slicks are changed out for wet tires with tread in the case of rain.

Over time the rubber used in normal tires has been exposed to hundred or thousands of heating and cooling cycles, degrading the material. The weakened material, while providing a greater surface area as the tread wears down, provides less friction than fresh rubber.

Treads on a tire serve to to prevent hydroplaning in the rain and other slick conditions.

Racing slicks are also composed of a softer compound and are designed to work at high temperature which softens it further increasing grip.

Slicks are also not designed to go 40k miles. As your car tires are used they heat up. Over time this constant heating and cooling causes the rubber to harden further. By the time your tires are bald they will have hardened to a point where the is actually less friction than on slicks.

Treads are for when road conditions are leas than ideal. They help manage hydroplaning on water and slippage on snowy roads. They have different compounds depending on the performance requirements of the vehicle. Harder compounds help the tires to last much longer while sacrificing traction performance. Softer compounds grip the road much better, giving much more traction but wear down more quickly.

Slicks are typically used only under dry ideal conditions. A slick tire on a wet road surface skims over a film of water like a water ski would, completely taking away one’s ability to gain traction or even more importantly steer.

Formula one racing is a good example showing the power of treads. They will race even in the rain, but they change to a treaded tire designed to channel water from the center of the tires outward allowing the most tire/asphalt connection possible for maximum grip.

Slick tires *do* give more grip for the reason you mentioned. The big caveat to that is that’s only true on roads that are completely dry.

If your cars tires didn’t have tread blocks on them, you’d immediately die when it rained because your tires would have no way to channel water and you’d just hydroplane and crash. The entire purpose of having ‘channels’ on your tires is so that when you’re driving on wet roads, the water can escape through the channels instead of you just hydroplaning on top of it.

On passenger cars, it’s far more important to have tires that work in numerous different conditions than to extract the most performance possible on dry roads.