An intriguing Grand Prix is about to take place at Silverstone. Max Verstappen and Lando Norris, the main protagonists of the past two months, start again side by side on the second row, ready to put pressure on the Mercedes of Lewis Hamilton and George Russell. All this with unpredictable weather, which, just hours before the start, outlines three possible scenarios for the race. We discuss this with Simone Berra, Chief Engineer at Pirelli.
Intermediate tires to manage
The first scenario is a fully wet British Grand Prix. According to Simone Berra, the use of extreme wet tires seems unlikely: “We do not expect the full wets to be used much. Silverstone is a high-severity circuit, and the full wets tend to overheat quickly, not requiring tire warmers, which makes their use unlikely.” More than overheating, however, the major issue with the full wets would be visibility: “The crossover would be at 120%, but we expect that once those conditions are reached, there would no longer be the necessary safety to race.”
In case of a fully wet race, the intermediate tire appears to be the most suitable, but still incapable of completing the entire race distance: “In Saturday’s free practice, some simulated stints, and we saw that after 20-21 laps, the front left was already at its limit in terms of wear. It also depends on the amount of water on the track,” explains the Pirelli engineer. “In FP3 yesterday, the track was drying, and obviously, wear increased. However, we did not see graining, which is positive. In wet but not fully soaked conditions, the intermediate tire does not allow for a single stop, which would become feasible in fully wet conditions. All teams, however, have three sets of new intermediates, so they are well covered for the race.”
Mixed conditions
The second possibility, and the most likely, is a Grand Prix with mixed conditions, with probable transitions from intermediates to dry tires. The crossover time between the two tires depends on weather conditions and fuel load, but Berra offers some references: “With little fuel on board, the crossover time between intermediates and slicks ranges from 1’35” to 1’36”. Generally, however, the crossover is around 110% compared to the reference time with slicks.”
The possibility of going to the end once the slicks are mounted will depend on the crossover point. Simone Berra continues: “Wind and sun will greatly influence the track’s drying speed. If it goes beyond the 15th lap, one could consider mounting a hard or medium and going to the end. The problem is that in the case of an intermediate-slick transition, some parts of the track may still be damp, and we know that the medium and hard have a slower warm-up process compared to the soft, which could struggle in the first laps. The soft would guarantee more grip and allow pushing immediately, but if changed early, around the 15th lap, it would not allow finishing the race.”
Pirelli also explains that, in addition to pit stops, another important strategic variable will be the choice of inflation pressures in anticipation of rain: “In case of wet conditions, increasing the pressure helps to decrease the contact patch and accelerate the warm-up process, as more heat is generated,” Berra illustrates. “This helps to have a more ready tire at the start or in case of rain in the first laps: if ambient temperatures drop, the tire would remain warm. In damp conditions, however, tire pressures would tend to rise too much, resulting in a loss of grip and suffering from graining. In that case, it would be better to start with lower pressures to keep temperatures under control.”
Three slicks in play
Even if the weather is favorable, the race would still be strategically lively, with all the compounds brought by Pirelli potentially usable: “If the race is dry, we expect a single-stop strategy, but with all compounds in play. The hard and medium are more resistant to graining than the soft, with the hard also more resistant to thermal degradation. On the other hand, the soft guarantees more grip at the start but would require more management. Due to the cold and suboptimal track conditions, we saw some graining in Friday’s simulations, which we expect today on the rear but especially on the front left, which is heavily stressed.”
“The fastest strategy on paper is to start with the softs and then switch to the mediums, very close also to the soft-hard,” continues Simone Berra. “The option of starting on mediums and finishing on hards is slightly slower but also more consistent, requiring less management. It also widens the pit-stop window. One would give up some grip at the start, but could extend the stint in anticipation of possible rain.” The race promises to be spectacular and unpredictable, starting at 4 p.m.
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