is often a limit on the size of the fuel tank, so many races require multiple stops for fuel to complete the race distance in the minimum time. Changing tyres is also common, to permit the use of softer tyres that wear faster but provide more grip, to use tyres suitable for wet conditions, or to use a range of tyres designated by the rules. Teams will aim for each of their vehicles to pit following a planned schedule, with the number of stops determined by many factors, such as fuel capacity, tyre lifespan, and the trade-off between time lost in the pits versus time gained on the track due to the benefits of pit stops. Choosing the optimum pit strategy of how many stops to make and when to make them is crucial in having a successful race. It is also important for teams to take competitors' strategies into account when planning pit stops to avoid being held up behind a competitor where overtaking is difficult or risky. An unscheduled or extended stop, such as for a repair, can be very costly for a driver's chance of success, because while they are stopped for service, competitors remaining on the track are gaining time on them. For this reason, the pit crew often undergo intensive training to perform operations such as tyre changes as quickly as possible, leading to pit stops, for example, as in Formula 1, where the car is only stationary for a few seconds for a regular pit stop. General strategy In any racing series that permits scheduled pit stops, pit strategy becomes one of the most important features of the race; this is because a race car travelling at 100 miles per hour (160 kilometres per hour) will travel approximately 150 feet (45 metres) per second. During a ten-second pit stop, a car's competitors will gain approximately one-quarter-mile (400 metres) over the stopped car. However, the car that made the additional pit stop will run faster on the race track than cars that did not make the stop, both because it can carry a smaller amount (and thus lower weight) of fuel, and will also have less wear on its tyres, providing more traction and allowing higher speeds in the corners. In racing series where teams have their choice of different compound tyres, the lower tyre wear may be enough to allow the team to choose