Brazillian Grand Prix: Strategy Predictions

Posted on November 23, 2011

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There are a few different considerations for the Brazillian race – the weather, Pirelli’s new tyres and safety cars. However, the impact of these is not quite as it may initially seem. The basics are that the fuel penalty is reasonably low (somewhere around 4.5 s in the early laps) and that the pit stop penalty is reasonably low at about 20s expected loss time for a good stop.

The weather is a difficult one to judge – there are possible showers on Saturday and Sunday, so the teams’ nowcasting will come into play, but the intermediate Pirellis seem to last well so it will be a case of the changeover occurring when the tyre temperature can be maintained in the slicks to generate the grip. Evidence from past races (Silverstone and Hungary especially) suggests that the switch to slicks has been made too late (even for the earlier stoppers) and so the gains from an aggressive switch could be quite big if no-one else is brave enough to follow. And you stay on the track. The evidence from previous races suggests that the intermediate tyres will last as long as needed – but sustained running at close to slicks conditions could cause some changes to new inters. The teams will want to avoid this if at all possible.

As far as safety cars are concerned, there have been a reasonable number of appearances at Interlagos over the years, but they are skewed very heavily to being in the opening laps. There are only a couple of occurrences outside the first few laps in the last ten years. A one-third to half race distance safety car appearance could help a car on a one stop strategy. Otherwise starting on the harder tyres (if they turn out to be much slower) is an option to get onto faster tyres for the rest of the race if a one-stop seems possible.

The factor against this seems to be that the new soft tyre Pirelli are bringing seems to be more durable and less quick that the old soft. This is likely to mean that the gap in pace between the tyre types is smaller. If we remember that the front runners tend to run on used softer tyres (which are about 0.3s per lap slower than new tyres) and on new hard tyres, it is possible that the harder tyres could be a realistic option for long stints in the race.

Since the last race I’ve written a basic strategy optimiser. I make some basic assumptions on degradaton and pace of the tyres, and I don’t need to pass it through the intelligentF1 model to get the predictions. So for an initial assumption set (harder tyres 1s slower, high degradation about equal to fuel loss, tyres last as long as we like), we get:

2 stops (option-option-prime) and 3 stops (option-option-option-prime) are almost identical, and a one stop is 17s slower. However, the degradation is likely to be less than this. The impact of reducing the degradation is seen in the table below:

.                  ‘high’ deg         ‘medium’ deg      low ‘deg’

1 stop           +17s                     +7s                    +0s

2 stops          +0s                     +0s                    +4s

3 stops          +0s                      +7s                   +20s

So if the degradation is about the level seen in India, a one stop becomes optimal. The most likely scenario is the ‘medium’ degradation, and then all three strategies are competitive. The teams will tend to go conservative as fewer stops tend to be favoured by both safety cars and traffic effects as the cars have track position for more of the race.

Now if we stick with the ‘medium’ degradation, and change the competitiveness of the hard tyre, we get the table below:

.                  0.5s slower         0.8s slower      1s slower

1 stop           +0s                      +4s                    +7s

2 stops          +0s                     +0s                    +0s

3 stops          +10s                   +8s                    +7s

With a close performance in the tyres, the one-stop becomes the pragmatic choice. So unless there are issues with tyre lifetime, I would expect many of the teams to seriously consider a one-stopper. Considering the tyre lifetime, if we cut the expected lifetime of the softer tyres to 30 laps there is no real change to the story as long as the harder tyre can do the rest of the race. Less than 25 laps from the softer tyre and two stops becomes the order of the day.

So unless the degradation is significantly higher than expected, which we should be able to tell on Friday, it’s looking like a one or two stop race. Or it might rain, in which case anything can happen.

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