stays out on their older tyres longer and laps fast enough to maintain or even extend their advantage over the car behind—this strategy may be successful if the leading car's tyres are still in good shape when the car behind pits, sufficiently so that the leading car can push without being overly limited by tyre degradation, or if the car behind gets stuck in traffic, thus negating their ability to utilise their fresher tyres to their advantage. Refuelling Refuelling, now banned in F1 races, was permitted from the 1994 season to the 2009 season. During this period, a pit stop involved about twenty mechanics, with the aim of completing the stop as quickly as possible. Stops generally lasted for six to twelve seconds, depending upon how much fuel was put into the car. However, if there was a problem, such as a fuel pump failing or the engine stalling, or repairs having to be made, it could take much longer. Cars were fuelled at a rate of more than 12 litres per second. This was accomplished by a fairly complex closed system that pumped air out of the car's fuel tank as the fuel was being pumped in. Since fuel was a significant portion of a car's weight, teams varied the amount of fuel loaded into a car at any given stop (and prior to the race) and thus vary the number of pit stops. The most common strategies seen were one-stop and two-stop strategies; two-stop strategies were employed to increase the car's speed/improve lap times to catch cars ahead, whereas one-stop strategies were used to gain time and track position to cars ahead with the advantage of one fewer pit stop. However, teams could and sometimes did opt for unorthodox pit strategies with multiple (3+) pit stops, as was employed by Ferrari and Michael Schumacher with four stops at the 2004 French Grand Prix, which he eventually won. As refuelling was a potentially hazardous situation, the mechanics wore fire-resistant multi-layer suits and flame-resistant gloves, long underwear, balaclava, socks and shoes, which had to meet the guidelines set by FIA Standard 8856-2000. Formula One pit crew roles Four wheel-gunners or tyre changers, one for each wheel/corner of the car, use a pneumatic wrench ("tyre gun") to remove the car's single locking lug nut from each tyre then reinstall it on the new tyre. Eight tyre carriers are used (four each