On June 18/19, Porsche will be competing at the 24 Hours of Le Mans with the 919 Hybrid for the third time. The young team is defending its title in Le Mans and in the FIA World Endurance Championship (WEC), for which this classic in France is the most important race. With its 17 overall victories, Porsche is also record holder on the Circuit de la Sarthe and leads in both the manufacturers’ and drivers’ classifications of the 2016 World Championship.
The pressure before the start is tremendous. To master it, the racing strategists in the Porsche team need maximum control – not only of the two highly complex prototypes of Timo Bernhard (DE), Brendon Hartley (NZ) and Mark Webber (AU) with start number 1 and the sister car of Romain Dumas (FR), Neel Jani (CH) and Marc Lieb (DE) with number 2. Many other factors have to be calculated into the process as well.
Team Principal Andreas Seidl is a Bavarian by birth and a strategist by calling. Together with the engineering staff – Chief Race Engineer Stephen Mitas (AU), Strategy Engineer Pascal Zurlinden (FR) and Vehicle Race Engineers Kyle Wilson-Clarke (GB, car number 1) and Jeromy Moore (AU, car number 2) – Seidl plans the optimum approach ahead of the race like a chess player in countless ‘what-if’ scenarios. After the race begins, however, the game is a question of reactions. It depends on the correct decision for each situation.
Factor 1: The refuelling stop
The first limiting parameter in planning the race is the distance between the refuelling stops. Since the maximum consumption values for fuel and electrical energy per lap are specified in the WEC, the latest point for refuelling is known. The strategists also know this information for their rivals’ vehicles. On the 13.629 kilometre lap in Le Mans, the Porsche 919 Hybrid covers a maximum of 14 laps with a full tank of 62.5 litres.
During the 24-hour race it will not be possible to divide the distance covered at the end exactly by these 14 laps. However, the aim is for the car to cross the finishing line with practically the last drop of fuel. This is because the less fuel there is in the tank, the lighter and faster the car will be. Consequently, at some point in time there will be a refuelling stop where the tank is not filled completely. The most suitable point for this to happen needs to be well thought-out. If a race proceeds without any incidents, this short refuelling stop is saved to the end. However, any changes in the weather or neutralisation phases may result in time savings if the stop is brought forward and combined, for example, with a change to rain tyres. The decision is made within seconds. A simulation programme, that is constantly fed with information by strategy engineer Zurlinden, helps in the process. The data at his side is from his own cars, observations of the competitors and the meteorologists.
Factor 2: The tyre change
The second basic parameter for the racing strategy is the performance curve of the tyres, which is where the expertise of the Michelin engineers comes to bear. The greater the wear on the tyres, the worse the lap times will be. This deterioration must be weighed up against the time lost by a tyre change in the pits. Tyre degradation does not always take place in a linear manner. Sometimes the rubber experiences a low point after a few laps, but then recovers again. At the same time, the car becomes lighter with every lap – this can also have the effect of extending tyre life. Andreas Seidl quotes figures: “In Le Mans in 2015, our longest distance with one set of tyres for a car was 54 laps. This means we refuelled three times without changing the tyres. From their best to their worst performance – adjusted for the effects of fuel – the tyres lost roughly 1.6 seconds per lap. The difference in weight of 44 kilos between full and empty tank accounts for about two seconds per lap.