# How do tire grooves/treads provide more grip?

I've never really understood how having treads on a tire. allows more grip in wet conditions; surfaces with water on them. What I know is that the water gets into those spaces and is forces out of the sides openings of the treads. I understand that but how does that create more grip. At the point the the tire hits the water, then It's already hit the water so the friction is not there. is the purpose of removing the water intended for clearing it for the rear tires. Like the front tires clear the water so the rear tires have a drier area to drive on?

• Wikipedia Nov 14 '20 at 13:40

Wet conditions means that there is a film of water on the road. There is very little friction between the tire and the water film, in order to get some grip, the rubber needs to touch the asphalt.

The treads help moving the water out of the way either by pushing it out sideways or simply giving it a place to go that's not between the rubber and the asphalt.

• I understand the concept. I just can't see clearly how it moves the water out before the tire actually touches the water itself. by the time the tire touches the water (it has touched the water*). It's like a paradox to me. the tire wants to contact the asphalt and not the water but to do this it has to touch the water to move the water out. am I crazy. Nov 15 '20 at 14:31
• The tire touches the water first but the treads allow the tire to move the water out of the way and to make contact with the asphalt underneath. Keep in mind that only applies when driving (fast): when you are standing the rubber always gets down the asphalt but if you drive quickly a spot on the tire touches the road only for a very short period of time. The treads help the watr to get out of the way quickly. Nov 15 '20 at 21:04

Here is another effect which is very important in the design of tires.

The surface of a smooth rubber tire is resistant to deformation because when squeezed in compression, the rubber wants to expand sideways, and the presence of more rubber next to the squeezed part resists this.

By cutting slots into the tire surface, the rubber can expand sideways while being squeezed in compression and the surface of the tire is thereby made softer and it can better conform to asperities in the road surface, and therefore raise the coefficient of friction.

This is preferable to compounding the rubber in the tire surface to be intrinisically softer, because soft rubber wears off the tire much faster than hard rubber does.

More slots mean better grip, up to the point where the tire surface area becomes dominated by slot area and not rubber. In this case, putting on the brakes tends to shear off the protruding treads and tire performance gets worse, not better.