Part science, part magic - a decent strategy is essential to the business of winning races. Or, indeed, losing them. The basic variables of the equation are simple enough: fuel load and tyre wear. But from then on, it gets vastly more complicated. Shortly after the reintroduction of fuelling stops to Formula One racing, the teams' race strategists worked out that at some circuits benefit could be gained from making two or three stops, rather than just one. This was because the car could run substantially quicker on a lower fuel load (with less weight to carry around) and using the grippier, but less durable, soft tyre compounds. A difference in performance that could be sufficient to offset the effect of the 30 or so seconds lost making a pit stop. Strategy continued to evolve, especially when it became obvious that certain teams were carefully working out just where in the order their driver would re-emerge after a stop. This allowed a car being baulked by a slower but hard to overtake runner to pit early, return to clear track and then put in faster laps that would ensure emerging ahead once the slower car made its stop - ‘overtaking in the pit lane’ as it has become known. This called on rigid pit stop timetables to be abandoned and replaced by a looser system of pit stop ‘windows’, with a number of laps on which a car can make its stop to gain best strategic advantage. And the move to a single tyre supplier in 2007 has forced teams to once again re-evaluate their race strategies, in light of all their rivals running on the same rubber, and the requirement for all drivers to use both the supplied specifications of tyres during a race. Data such as weather forecasts, the likelihood of overtaking at a particular track, the length of the pitlane and even the chances of an accident likely to require the use of the safety car all come into play when deciding strategy. And, of course, one of the largest ingredients remains, as always, luck.