Choosing the number of stops

Pit stops are not actually compulsory in Formula One. In theory, a team could build a car with a big enough fuel tank to do the whole race without stopping, and the tyre manufacturers could easily produce a compound tough enough to make tyre changes a thing of the past. But in reality, such a car would be hopelessly off the pace. Not only would it be slow because of its weight and hard compound tyres, but the bulkiness arising from its big fuel tank would make the car aerodynamically inefficient, slowing it yet further � and all the other teams would laugh at them. All current Formula One cars are therefore designed around tanks that are too small to hold enough fuel to complete a full Grand Prix.
At most tracks, a pit stop � including slowing down, stopping, re-fuelling, and accelerating back up to speed � takes around 30 seconds. The race distance is specified as the least number of laps exceeding 305km (190 miles). (For more on what constitutes a �complete� race, head to �race stoppage� later in this chapter.) Over that distance, and with that time penalty, it did not use to be worthwhile stopping more than twice. But since the 2003 regulations prohibiting fuel loads being changed between qualifying and race (see Chapter 8), stopping three times in a race has become a viable option once grid position is taken into account. Stopping just the once, or even twice, during a race has fallen out of favour after the introduction of these regulations. At some tracks an extra stop is quite feasible, more than making up the extra 30 seconds of pit stop time with a lighter fuel load. Magny Cours, in France, with its very short pit lane and high tyre degradation, is a good example of this. At other tracks the tyres perform close to their peak for longer and the pit lane can be longer. Silverstone in Britain is a good example of this. The most common strategy in Magny Cours is three-stops, whereas for Silverstone two stops is more popular.
Aside from tyre behaviour, it�s all to do with fuel consumption and how much lap time the extra weight costs you. In other words, a team needs to know how sensitive the car�s lap time is to changes in weight and how fast that weight is changing.