Cars have tires for two purposes. They help absorb the shocks of traveling on bumpy rocks by acting as a cushion and they give the cara good grip on the road surface. Thin cuts in the rubber act as sponges, which soak road water. You will also notice patterns on the tire treads. Those patterns are designed to squirt water behind when tires revolve at high speed. Since car races are usually held on dry roads, racers usually use treadless tires called slicks. Treadless tires, plus their extra width, give maximum possible contact with the race track. During heavy rains, pit crews replace smooth tires with treaded ones to maintain control. When water builds up in front of the slicks, the driver looses control of the car. When this happens, the car skates ahead and a collision with the wall or with another car is most likely to happen.