You must have noticed that the racing car tires are made of rubbers, but without any treads. But why is it so? To answer this we have to compare Racecar tires and passenger car tires with the help of the Physics of Car Tires (based on Friction).
In other words, we will discuss the topic: Road Tyre vs. Slick Tyre on the basis of frictional force.
For many pairs of materials, the force of static friction or kinetic friction acting on an object is not affected by the amount of surface
area in contact with a surface. Instead, the coefficients of friction depend on the types of materials in contact. The magnitude of static friction or kinetic friction only depends on the coefficient of friction and the magnitude of the normal force.
However, rubber is an exception. For example, the magnitude of static friction acting on a rubber tire on a road surface depends on the surface area of the tire that is in contact with the road. That is one reason why race cars have very wide tires with no treads.
Racecar tires versus passenger car Tires | Slick Tyre vs. Road Tyre – based on frictional force
Now let’s compare racecar tires (or slick tires) with road tires (or passenger car tires) on the basic of friction physics.
Racecar tires made of rubber are designed to maximize the surface area in contact with the road, which increases the magnitude of static friction acting on the tires and also dissipates heat more quickly. This, in turn, helps race cars move along curved paths without slipping. If it starts raining during a race, the event is sometimes postponed because these types of tires have no treads.
Unlike race car tires, the tires on passenger vehicles need to provide good traction (force of friction) on road surfaces under all weather conditions. The tread area on a tire has small and large grooves (Figure 1). Grooves provide pathways for water, such as rain and snow, to pass beneath the tire as it rolls over a wet road. This helps the tire maintain contact with the road. As a result, the magnitude of friction acting on the tires is usually large enough for safe driving.
The physics of car tires – use case on a wet road explained | tire tread, grooves, friction, and hydroplaning
When driving at a low safe speed on a wet road, the water level in front of a passenger car tire is low (Figure 2(a)). The water has time to move through the grooves in the tire tread and be squeezed out behind the tire. In this situation, friction from the road still acts on the tire.
If the driver starts to speed up, some of the water in front of the tire will not have enough time to pass through the grooves toward the back of the tire (Figure 2(b)). This causes the water level in front of the tire to increase. This excess water causes the tire to start to lose contact with the road. If the driver’s speed continues to increase, the water level in front of the tire will increase to the point where the tire no longer directly touches the road surface (Figure 2(c)).
Now the tire experiences no friction from the road and very little friction from the water. An object experiencing no net external force will continue to move at constant velocity. The two materials in contact are now rubber and water, not rubber and the wet road. This situation is called hydroplaning and is very dangerous. It results in the driver losing control of the vehicle and being unable to slow down due to the very low friction acting on the tires. The only way to avoid hydroplaning is to drive slowly when the roads are wet.
The tread depth on passenger car tires is usually 7 mm to 8 mm for a new tire. As the tires wear, the tread depth decreases, and less water is able to move through the grooves. Driving with worn tires increases the chance of hydroplaning. When the tread depth gets too low, the tires should be changed.