Each LMP2 car has 16 sets of tyres at its disposal during the race. The performance of Le Mans prototypes can evolve dramatically during the course of the 24 hours. Britain’s Sam Bird, who shares the G-Drive Racing entry with Julien Canal and Roman Rusinov, says the opening stints of the race will be crucial in understanding more about the level of tyre wear.
“We had restricted running in both test days, so we’re actually a little unclear on the exact life the tyre has. We know that it is long, but we don’t know precisely how long,” he explains.
“So at the beginning of the race we will probably do a double-stint and then change tyres so the guys at Dunlop can examine the rubber and give us an exact reading on exactly how far they think our tyre will go while maintaining a good speed.
"After we’ve found that information out, our pitstop strategy for the rest of the race will be more dictated by fuel rather than the tyres.”
There are also some techniques the driver can use to preserve the rubber for as long as possible. Bird says: “We speak about ‘spin time’, which means trying not to overwork the [driven] rear tyres. But because of the long straights at Le Mans, the tyres get to cool down quite a bit on each lap.
“Another thing that we could see from the front tyre during the race is some cold graining, especially between 2am and 7am in the morning.
"We could find that on the first lap, if you’re pushing too hard, especially on corners such as Tertre Rouge, you could start to overstress the skin of the tyre on the exterior and grain the front left. This would mean you’re then going to have understeer for the remainder of your stint.”
Dreaded understeer can play a significant role in tyre management. Rees says: “If a car is bottled up behind another car, it can pick up understeer due to the aerodynamic imbalance. So if you’re in the middle of a triple-stint and the driver is experiencing understeer, he can damage the tyres and might have to pit early because the lap times could drop off.”
Although it’s inevitable that the tyres will wear out over the course of a long stint at Le Mans, any drop-off in lap times can be mitigated by other factors, says Bird: “These tyres can maintain a good level of grip for many laps and although we might lose a little bit in the corners as the tyres wear, we gain on the straight because the car gets faster as the fuel load decreases.”
An entire day of racing around such a long circuit inevitably means incidents, and these can impact on other cars at racing speeds. Le Mans tyres are fitted with a Type Pressure Monitoring System (TPMS) which informs the engineers back in the pit garage about any fluctuations in tyre pressure. This can warn a team about a potential slow puncture inflicted by debris on the track.
“We know from experience that the gravel traps and run-off areas contain flint and through all of the practice and qualifying sessions we’ve seen cuts to the tyres. We’ve had no punctures caused by that, but we’re absolutely aware of that if a car goes off track and brings the flint back onto the circuit,” says Rees.
Ultimately, Dunlop learns lessons on the circuit that can transfer back to its standard car tyre range. Rees says they especially look at “materials, compounds and polymers” in terms of the technology transfer – which means running over a flint chipping in your road car shouldn’t spell the end for your rubber.
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