Chinese Grand Prix: Strategy Options

Posted on April 13, 2013

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Qualifying leaves us with a fascinating race in prospect. Personally I’m surprised that only three cars went for the mediums in Q3, and my initial feeling was that Vettel and Button look good for the race tomorrow. But do they? Well, I’ve had a play with the numbers, and I can give a few pointers from what we saw in the practice runs – but I can’t say everything because two very big variables will come in to play. The first being the degradation rate of the soft tyres which was very big on Friday, and the second being traffic. We are sure to see a lot of overtaking tomorrow, and it will be key to the outcome of the race how much time is lost by the fast cars when in traffic.

The soft tyre degradation, based on a number of cars, was about 0.8-1s per lap. Which is huge – it’s usually 0.08-0.1s per lap. And the first lap on the used softs (after the simulated qualifying run) was about the same speed as the first lap on the mediums for a long stint. So I don’t expect those on softs to disappear in the opening laps. In fact I expect that Vettel and Button could be making ground from as early as lap 2.

Based on last year’s race, we can also get some idea of the gaps between cars at certain stages of the race to get an idea of what sort of traffic issues might be faced when those starting on the soft tyres make their pitstops.

Using the intelligentF1 model to pick an optimal race strategy (excluding traffic issues) requires a few assumptions. Given that the track condition is likely to be better than Friday, I have reduced the soft tyre degradation to 0.7s per lap, but it could be much better (or worse) than this. It’s a big unknown.

The first picture below shows that if the tyres are good for 20 laps before phase 2 degradation, then three stops is better than two by about 20s. This case starts on options, but it works out pretty much the same for those starting on primes, except that they have the advantage of new tyres all the way. For each lap more the mediums manage, this gap comes down by about 4s. So if the tyres do 25 laps (and no, Hamilton did not do a 27 lap stint in FP2, it was 17 laps – I think it’s a typo from Autosport Live), then they come out within a couple of seconds. If the cars starting on options get past lap 25 (assuming a first stop by lap 5), they’ll probably be going for two stops.

2013_china_2

Now what happens if we assume a 3 stopper for both those starting on the mediums and the softs.  Let’s also give the leader an advantage of field spread – say 10 seconds worth over the first few laps – I expect that this is a little generous. Then, assuming identical underlying pace and no traffic effects, we get the following picture (the black line is the car starting on softs and the blue line the car starting on mediums). There is a big gain from the new softs at the end, but it is not enough (quite) to overcome the field spread with the assumptions used. It’s close though.

2013_china_3

So how will traffic affect things? This is a difficult one, but what we can do is to map the race of a car about 0.5s per lap slower on each strategy to see where they can interfere with the races of the fast cars. So I’ve added two lines to the chart – the red one starts on the soft tyres and the grey one on the mediums. I’ve offset them at the start by five seconds for field spread.

2013_china_4

What we see is that the cars starting on the softs will need to do some overtaking in the second stint (probably a lot as they will come out near the back of the field after their early stop), but those starting on the medium tyres have a good chance of clearing those cars at their first stops. Obviously, if the pace of the Ferrari (say) is only 0.3s off the Red Bull, then Vettel would have some overtaking to do, unless he is able to stay out longer.

Key to the race is the amount of time lost by the early stoppers in traffic – only 5s would mean more overtaking in the second stint, and be enough to drop them behind those starting on the medium tyres if they have the same race pace. And five seconds is not much. Webber stopped on lap five last year, and dropped to 20th. He then lost almost exactly five seconds in traffic in his second stint which dropped him behind the two-stopping Massa – which cost him another 4s. If a similar thing happens to any of the top four cars, then it would almost certainly cost them the win.

I guess that this supports what I thought to start with – the strategy of Red Bull/McLaren is the choice I would have made. It’s marginal, but I think that there is less to go wrong with it. However, I’m not convinced that the Red Bull is as fast as the Mercedes for race pace, and I think that the silver cars are still favourites as long as they make a good start. I don’t think Lotus have the pace based on Friday, and I am not convinced that Ferrari were looking after the tyres on Friday. But it’ll be close – and it could come down to overtaking prowess, which is a good thing in my book.

Having said all this, the soft tyres might last much better in the race, and the cars at the front might have an easy time of it. And Vettel and Button might crash into each other at the start.

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