Rain tyre

Rain tyres or Wet tyres are special tyres used in motor sport in wet weather as opposed to a slick tyre used in dry conditions. They are very similar in many ways to the tyres found on normal road cars.

Structure

Rain tyres have a specially designed structure making them better adapted for their application than any other tyres. However not all rain tyres obey the same design principles. Certain factors need to be taken into account when designing a good rain tyre, such as the:
*speed of the car
*weight of the car
*power of the car
*lifespan of the tyre

Grooves

Rain tyres are cut or moulded with patterned grooves or tread in them. This allows the tyre to quickly displace the water between the ground and the rubber on the tyre. If this water is not displaced, the car will experience an effect known as Hydroplaning as the rubber will not be in contact with the ground. These grooves do not help the car grip contrary to popular belief, however if these grooves are too shallow, the grip will be impaired in wet conditions as the rubber will not be able to make good contact with the ground. The patterns are designed to displace water as quickly as possible to the edges of the tyre or into specially cut channels in the centre of the tyre. Not all groove patterns are the same. Optimal patterns depend on the car and the conditions. The grooves are also designed to generate heat when lateral forces are applied to the tyre.

Rubber

Rain tyres are also made from softer rubber compounds to help the car grip in the slippery conditions and to build up heat in the tyre. These tyres are so soft that running them on a dry track would cause them to deteriorate within minutes. Softer rubber means that the rubber contains more oils and other chemicals which cause a racing tyre to get sticky when its hot. The softer a tyre, the stickier its gets, and vice verse with hard tyres.

hape

Sometimes rain tyres are designed to have a smaller diameter than their dry counterparts. This means that the wheel spins faster and more water is thrown off the tyre by overcoming centripetal force. Some rain tyres are also narrower than the dry counterparts. This smaller "footprint" reduces the chances of hydroplaning.

Intermediate Tyres

Some racing series such as Formula 1 allow an intermediate tyre. This tyre is designed to be used in conditions too wet for slick tyres and too dry for wet tyres. They are some sort of “in-between” tyre or intermediate tyre as the name suggests. They are made with rubber compounds slightly softer than slick tyres and are cut with grooves like the rain tyre but shallower to prevent excessive heat build up.

Events in rain tyre history

* The 2008 edition of the NAPA Auto Parts 200 featured the first points-paying race in NASCAR history to use rain tyres.