One of major functionality of the formula racing car tire is to generate traction (or friction) between the tire and the road surface. The greater the generated traction, the better the grip and hence the faster the car will go. Therefore, a softer rubber compound provides better grip and hence is faster and a harder compound comparatively provides lesser grip. Therefore it is slower.
But there is a catch. Soft tires wear a lot and it will finish sooner than the ones with harder compounds. In the same way, harder compounds are much more durable than the softer ones. Therefore, road going cars use much harder compound tires that will last several thousand miles.
Effect of weather on tire performance.
The below picture shows all the different tire compounds that tire manufacturer and current Formula 1 tire supplier Pirelli produces.
From the left we have –
Intermediates (Green Stripe)
Wets (Blue Stripe)
Super Softs (Red Stripe)
Softs (Yellow Stripe)
Mediums (White Stripe)
Hard (Orange Stripe)
Now those tires which do not have any grooves running through them (first four from the right) are called Slick Tires. These tires are used during dry weather. As soon as it starts raining, Slick Tires are rendered useless because when there is water on the track, there is nowhere for that water to go between the tire and the road. I mean to say that there are no channels through which the water in between the tire and road can be expelled.
The condition where a film of water separates the tire and the road, thereby causing a skid, is called Aquaplaning. (The physical definition of Aquaplaning is a little different but let’s leave that to the engineers to handle)
Slick tires therefore fail pathetically during wet weather. During such weather conditions, Racing Teams switch to the other compounds on the list – The Intermediate or the Wet tires. The former is for mildly wet conditions while the latter is during a full-fledged rain. These tires offer the much needed grooves (refer to the tires picture) in order to channel the water from between the tires to the sides.
Titbit- A wet weather Formula 1 tire can dispense up to 25 litres of water in a second during a race.
It has to be said though that the grooves cause a decrease in the surface area of the Rubber that comes in contact with the road in any given time. Therefore, wet weather tires on a dry track wear out much faster than slick tires. Much and more can be discussed about racing tires. But for a basic grasp of the concept, I believe I have done at least partial justice