Rain tires or wet tires ("tyres" in
British English
British English (BrE, en-GB, or BE) is, according to Lexico, Oxford Dictionaries, "English language, English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in ...
, commonly shortened to wets) are special
tyres used in
motorsport in wet weather as opposed to a
slick tyre
A racing slick or slick tyre is a type of tyre that has a smooth tread used mostly in auto racing. The first production slick tyre was developed by M&H Tires in the early 1950s for use in drag racing. By eliminating any grooves cut into the tre ...
used in dry conditions. They are very similar in many ways to the tyres found on normal road cars.
Rain tyres are not used in
NASCAR
The National Association for Stock Car Auto Racing, LLC (NASCAR) is an American auto racing sanctioning and operating company that is best known for stock car racing. The privately owned company was founded by Bill France Sr. in 1948, and ...
,
ARCA and
INDYCAR sanctioned races held on
oval tracks as these races are invariably halted when the track is wet due to safety concerns regarding the large amounts of spray involved reducing visibility, as well as a lack of traction in banked corners at high speeds.
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
Aquaplaning or hydroplaning by the tires of a road vehicle, aircraft or other wheeled vehicle occurs when a layer of water builds between the wheels of the vehicle and the road surface, leading to a loss of traction (engineering), traction that ...
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
Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, an ...
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 become sticky when it is hot. The softer a tyre, the stickier it becomes, and conversely with hard tyres.
When rain has stopped falling, and a track is in the process of drying, it is not unusual to see drivers intentionally driving through wet puddles and damp portions of the course, in order to cool the rubber and stave off tyre deterioration. As soon as possible, drivers will revert to slick tyres to maintain competitive speeds.
Shape
Currently, F1 rain tyres have a larger diameter than dry tyres, with the wets having a diameter of 10mm more than the slicks.
This increases the ride height of the car and makes it less vulnerable to aquaplaning.
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 One
Formula One (also known as Formula 1 or F1) is the highest class of international racing for open-wheel single-seater formula racing cars sanctioned by the Fédération Internationale de l'Automobile (FIA). The World Drivers' Championship, ...
allow an intermediate (inter) tyre. This tyre is designed to be used in conditions too wet for slick tyres and too dry for wet tyres. 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. Former Formula One tyre supplier
Bridgestone referred to the "intermediate" tyre as the "wet" tyre, and to what are known as "full wets" as "monsoon tyres".
References
{{Tires
Tires
Vehicle modifications