Lewis Hamilton described the final lap of Sunday’s British Grand Prix as the “most dramatic ending I can remember”, which is quite a statement from a driver who won his first world championship in the final corner of the final lap of the season.
But as exciting as it was watching Hamilton wrestle his car to victory on three inflated tyres, no one wants to see a repeat when the sport returns to Silverstone this weekend. So, what do we know about the failures on Sunday and what might Pirelli do ahead of next weekend’s Formula One 70th Anniversary Grand Prix?
What happened to the tyres on Sunday?
Three cars suffered front-left failures within three laps of each other on the hard compound tyre when they were between 36 laps and 38 laps old. Two of those cars were Mercedes, which by virtue of being the fastest car on the grid put more strain through the tyres in high-speed corners, and the other was the McLaren of Carlos Sainz.
Pirelli put the failures down to the high wear levels experienced over a stint of nearly 40 laps at Silverstone combined with the extreme forces experienced around the 5.8km lap.
There was debris on the track from earlier incidents, most notably Kimi Raikkonen’s front wing failure in the high speed corners of Maggots, Becketts and Chapel, but Pirelli made no mention of that in its findings.
In normal circumstances, teams would not have attempted such a long stint at the end of the race, but Daniil Kvyat’s crash on lap 12 triggered a safety car that presented an opportunity to make a free pit stop. The trade-off was a 39-lap stint to the flag, although it should be noted that five of those 39 laps were completed behind the Safety Car, significantly reducing the strain on the tyre for the early part of the stint.
While the remaining 34 laps of the high-speed Silverstone at racing speeds would be asking a lot of the tyres, last year Mercedes completed a 32-lap stint on the exact same compound and construction to win the race, while Pierre Gasly managed 40 laps in the Red Bull and finished fourth. That data led teams to believe a single pit stop on lap 13 would be a viable strategy and, given the length of Gasly’s stint last year, relatively risk averse.
But a full year of performance development means the cars are as much as 1.2s faster than last year. In the case of the Mercedes, a lot of that performance has been found in high-speed corners, with the cars as much as 11km/h faster through challenging corners like Copse this year. Combined with the two Mercedes drivers trading fastest laps as they fought each other for the lead, the tyre had a much tougher life than it did 12 months ago.
That increased wear, which was visible by the lack of rubber left on the other front-left tyres that survived the race on other cars, resulted in less protection for the construction of the tyre, making it more vulnerable to a puncture.
What happens next?
F1’s decision to hold back-to-back races at Silverstone was made several months ago as the sport was looking to fill its revised calendar with as many events as possible. The circuit was an obvious target for two races given the presence of seven of F1’s teams in the U.K. and the fact it usually serves up good racing.
But the very nature of the circuit, with its multiple combinations of high-speed corners, was one of the main reasons behind Sunday’s tyre failures. What’s more, next week’s Formula One 70th Anniversary Grand Prix will see Pirelli supply a softer range of tyres — a decision taken prior to the season in the hope that the two races would not result in the same spectacle twice over.
On the face of it, it sounds like a recipe for disaster: less durable tyre compounds at the same high-energy circuit … not to mention a forecast of hotter weather. But using tyres that degrade more quickly may actually help the situation rather than make it worse.
Pirelli has five compounds in its range this year, named C1, C2, C3, C4 and C5, with C1 being the hardest and C5 being the softest. At the first Silverstone race, C1, C2 and C3 were on offer and named hard, medium and soft, but this weekend the C2 will become the hard, the C3 the medium and the C4 the soft.
First off, it’s important to make the distinction between degradation and physical tyre wear. Degradation refers to the loss of performance from the rubber and is usually a symptom of overheating. Wear is the physical shedding of rubber from the tyre, which is what made them prone to failure last weekend.
Degradation usually occurs when the tyre gets too hot, resulting in a chemical reaction in the compound that results in less grip. It’s the reason you hear drivers talking about the tyre’s “operating window”, which is essentially a temperature range in which the compound works best. Go beyond that window and the resulting chemical reaction means the tyre compound loses performance, sometimes irrecoverably.
Therefore, a tyre can suffer extreme degradation — to the point that a driver is forced to make a pit stop due to the loss of performance — without the tyre physically shedding all of its rubber. The selection of the C2, C3 and C4 compounds for the second race will lead to more degradation, meaning the useful performance life of the tyre will likely be shorter than its physical wear life.
“If we are talking about wear, it doesn’t matter if we go with the same compounds we used today or the softer compounds,” Pirelli motorsport director Mario Isola said last weekend. “Each tyre has a maximum number of laps, which depends on each car, it depends on set-up, level of energy, which is why we cannot say that the limit is the same for everybody.
“But if the issue is the wear, we don’t fix it with changing to same compound choice we used today.”
The theory is that the extra degradation will force teams towards a two-stop strategy for performance reasons, effectively ruling out the long 39-lap stint we saw on Sunday. The only downside to that theory is that the other two race tyres on offer, the C3 and C4, will also be weaker in terms of performance, to the point that teams may want to avoid using them as much as possible.
On Sunday, Romain Grosjean bucked the trend on tyre strategy by opting not to pit under the safety car for Kvyat. The Haas driver made a set of the C2 tyres last 36 laps before he had to pit, and did so while pushing hard to defend position.
Isola said Grosjean’s C2 tyres came back “completely worn”, but considering the relatively strong performance of the Haas, rival teams will look to that 36-lap stint as a marker for what’s possible this weekend. The temptation may be to spend as much of the race as possible on the C2s, because the other options — the C3 and C4 — will struggle with degradation. Therefore, its not beyond the realms of possibility that a perfectly sensible race strategy will see a set of the C2s reaching the limit of the wear life.
We saw a collective reluctance among the teams to use the C3 when it was designated as the soft tyre last Sunday. All teams outside the top ten had a free choice of tyre compound for the start of the race, and every one of them opted for the C2 over the C3.
The only drivers that used the C3 at all in the race were those in the top 10 that were forced to start on it under F1’s qualifying rules, and Max Verstappen and Valtteri Bottas, who both used it for two laps at the end of the race. But that same compound now becomes the medium this weekend, meaning even the most conservative strategies are going to be reliant on it in order to meet the mandatory regulation of using at least two different compounds in the race.
A likely strategy will be one stint on the C3s and two on the C2s, but the makeup of Pirelli’s tyre allocation this year means each driver only has two sets of hards (in this case the C2) for the entire weekend. That means anyone hoping to use both sets of C2s in their race strategy will not get a chance to use them in Friday practice, although it should be said they will have plenty of data to rely on from last weekend.
It all makes for an unusual situation to which the teams will have to adapt without pushing the tyres beyond their limit.
In order to help the tyres, Pirelli is making one significant change compared to last weekend by upping the prescribed minimum tyre pressure. Those settings are dictated by Pirelli ahead of each weekend and any team that goes lower than the prescriptions will be reported to the stewards and penalised.
Increased pressures are often used by Pirelli to protect the tyre at high-energy circuits where the construction is at risk due to the extreme forces acting upon it. Teams and drivers tend to argue against upping pressures as it offers less grip and can lead to more degradation, but those side effects are preferable to the kind of failures we saw on Sunday.
Last weekend, Pirelli only upped the front tyre pressures by 0.5 PSI compared to last year’s British Grand Prix, so it appears as though they still have a bit of wiggle room to play with before ruining the performance of the tyre completely. Nevertheless, if it leads to increased degradation we could see an unusually high number of pit stops on Sunday.
All of the above is probably not what F1 had in mind when it decided to change the compounds between the two Silverstone races, but it should still make for a fascinating spectacle. The hope is that we see more pit stops, greater variation in strategy and no tyre failures.