You can choose between four tyres - Soft, Medium, Hard and Wet. 

Soft tyres are the fastest but wear out quickly (you will need to pit stop earlier). Hard tyres are slower but last longer. Medium tyres are a combination of Soft and Hard tyres, their speed and duration between the two. Wet tyres give the best performance in wet weather conditions. Tyres can wear out quickly if the weather becomes hotter than usual!

If a race starts in the rain, the game will automatically select Wet tyres for the start - but you can still change if you want to.