Analysis: Which were the right and wrong calls in US GP thriller?

The US Grand Prix will long be remembered as a classic Grand Prix with multiple changes of leader and countless reversals of fortune.

It was another race, that Nico Rosberg worked hard to get into a position to win, but again it got away from him. The day ended with Lewis Hamilton crowned world champion for the third time, but it was also an outstanding race from a strategy and decision-making point of view. All of the menu of Strategy games and situations were in this race.

So why were some of the key decisions taken as they were?

Pre race considerations

Rarely has there been a Grand Prix with such a disrupted build up, in terms of track time before the race.

Appalling weather conditions saw Friday’s FP2 session cancelled while Qualifying was postponed to Sunday morning. There was no dry running at all and only limited wet laps on Friday and Saturday mornings.

So no one had any idea what would happen as the cars lined up on Sunday for the race, an hour after the rain stopped, on Intermediate tyres on a wet track. Everyone was looking for the right moment to switch from intermediates to slicks.

The race can best be viewed in four parts with a series of Safety Cars and Virtual Safety cars as the turning points of the race.

Part 1: Hamilton grabs control at the start

The first part of the race was held in wet conditions, with the track drying slowly. Lewis Hamilton started second behind teammate Nico Rosberg, but got the better initial getaway and then with an aggressive lunge into Turn 1, in which the cars touched, he took the lead.

But the Red Bull was better suited to the intermediate conditions and Ricciardo took the lead.

The track dried slowly; the first sector was ready for slicks before the other two, with the long right-hander at Turn 17 the most stubbornly damp part. Drivers who tried slicks too early like Bottas and Grosjean, were markedly losing time there.

It was only when Marcus Ericsson began to show a step-change in lap times on slick tyres that the moment was right. Mercedes called Hamilton in on Lap 18, but Rosberg passed him after the call was made, when the cars were in Sector 2. After the mix up at Bahrain in 2014, Mercedes initiated a new procedure for preparing tyres and timing the call for the leading car on track, which they stuck to here, meaning Rosberg went around again.

As it turned out Hamilton struggled to warm up his new soft tyres on the out lap and when Ricciardo, Rosberg, Kvyat, Perez and others came in a lap later, Hamilton dropped to fourth.

Rosberg was immediately fast on soft dry tyres and sped away.

Part 2: Safety Car creates a chance for risk and reward

When the Safety Car was deployed on Lap 27, a number of strategists spied an opportunity. With 29 laps to go it was too early for most to consider being able to reach the end on a set of tyres.

Ferrari pitted Vettel for Medium tyres, thinking they might go to the end. Perez did the same for Force India as did Sainz, Rossi and Hulkenberg.

Toro Rosso did what they usually do in these circumstances and split the strategies with Verstappen left out for a lap while they looked at what others were doing and then they pitted him for softs. This was to work out exceptionally well for the Dutchman, as 10 of the next 28 laps were conducted at reduced speed with VSCs and Safety Cars.

The option was there for Mercedes to split the strategies, putting Hamilton onto Mediums at this point, which would possibly have reduced the risk of the strategy they went with from this point. But a further VSC and Safety Car helped them out and anyway the Mercedes had exceptional pace on slick tyres, so they got away with it.

The risk came from the fact that most of the cars they were counting on to be between them and Vettel at the restart also pitted or were very slow at the restart, like the Red Bulls. It meant that they had to push hard after the restart to get control of the race.

Why did Mercedes opt not to pit either car? The medium was not attractive as it would be slow to warm up at the restart and the driver would be a sitting duck at the end on worn mediums, against drivers coming through on newer softs on their 2 stop strategies. Mercedes did not want either of their drivers to be in that position.

If anything Hamilton was looking the weaker driver at this point, as Rosberg had better pace on the soft tyres. For the second race in succession, this should have been Rosberg’s race. But fate and a further Safety Car would put paid to that.

At the restart Rosberg and Hamilton romped away; they had pulled 10 seconds on the field after just 5 laps. Then there was another twist.

Part 3: What, another Virtual Safety Car?

Nico Hulkenberg’s car was stranded on track and so a Virtual Safety Car was employed on Lap 38. This was in the pit window to go to the finish on a set of soft tyres, so a number of cars pitted, including Rosberg.

Stopping under a VSC means that a stop takes only 12 seconds instead of 21 secs. Red Bull opted to bring both cars in and stack the second behind the first.

Mercedes did not do this because they felt that the risk outweighed the reward. Coming in slowly as the second car and waiting for service costs the second car around around 6 seconds; that means a net saving of just 3 seconds on a normal stop and with a 25% chance of a delay on the stop the gain is marginal compared to stopping at racing speed at the optimum moment. So Hamilton was left out.

He now led the race with another stop to make, with Vettel on medium tyres five seconds behind him and Rosberg on new softs a further three seconds behind and in the best shape of the three of them. So this was now firmly Rosberg’s race.

Red Bull’s challenge had faded dramatically by this point; fast on the intermediates, they were slow on the slicks, struggling to get them in the right working range.

Part 4: A second Safety Car, a gift to Hamilton

Austin doesn’t have a particularly high risk of Safety Cars, as the run off areas are massive. The main risk is at the start and the opening laps. After that it’s rare to have a Safety Car.

However what we saw on Sunday was a situation where the tyres on various cars were going off at different rates, at the same time as the field was bunched up or slowed by Safety Cars and VSCs. On top of that, with so little information on the slick tyres after wet practice sessions, some teams were trying to do things with tyres that were optimistic,

All of this led to incidents and accidents.

Daniil Kvyat crashed with 14 laps to go, bringing out another Safety Car. Hamilton had one more stop to make and he took the opportunity to pit. It put him right behind Rosberg on tyres that were five laps fresher. Vettel also took the opportunity of a free stop to switch to soft tyres.

Everything Rosberg had done to get himself back to a winning position after being punted by his teammate in Turn 1 at the start was now negated and the advantage was with Hamilton.

But then Rosberg made an error after the restart in the nine-lap sprint to the finish and Hamilton gratefully took the gift to win the race and clinch the title.

Behind him Vettel closed on Rosberg on his newer tyres, while Verstappen was still going strong on his original softs from the first Safety Car period. Sergio Perez was behind him on the original mediums from the same episode, again a masterful piece of driving as well as great Strategy by Force India.

And Carlos Sainz came in sixth, having started 20th; but he was demoted to seventh for a pit lane speeding penalty, after executing a sub-optimal three stop strategy.

The UBS Race Strategy Report is written by James Allen with input and data from several F1 team strategists and from Pirelli

Kindly provided by Williams F1 Team - Click to enlarge

Look at the pace difference between the Mercedes and Red Bulls on intermediates at the start and then on slicks later in the race.

Look at the degradation for Vettel on the medium tyres in the third quarter of the race. He was lucky to have the chance to stop again for slicks near the end, although he had no real challenger behind.