As the second (and final) pre-season test at Barcelona is now underway, this will the last post on the first Barcelona test. Two sets of long runs were particularly noted in the comments, demonstrating how difficult it is to assess the pace of the cars from simply the laptime data. These data belong to Massa and to Rosberg. The idea of this post is to present the graphs of the data in such a way to show what I was thinking (rightly or wrongly) in my interpretations of the data, and to make it a bit clearer how I have tried to understand the data.
So firstly, Massa. The question here is whether he refuelled after his first run. What I have done is plotted his three runs on the equivalent of a race history chart (in red), plotted the intelligentF1 model curve fits (should match the gradients of the data – the time lost/gained in fictional pitstops is not relevant here) and as a check, I have plotted the second stint (minus slow first timed lap) over the first stint in blue – these should be close if the Ferrari is refuelled to it’s original fuel load.
So what we have is a first stint which has two speeds – this is not a typical trace and this step change is not tyre related. A reasonably consistent fast pace for the first few laps, and then a slower, but reasonably consistent pace for the remainder. Rightly, or wrongly, I chose to fit the slower pace as usually in the races, this is more indicative of the true pace over a stint. The fits for the second and third stint are pretty good – the trace at the end of the second stint is more indicative of the tyres going off more quickly as the trace gradually bends away from the fit. The curvature of the line gives the difference between the gain in pace due to fuel burn and the loss in pace due to tyre age. Generally, the stints are getting slower, so the tyres are losing pace faster than the gain from the effect of fuel load reduction.
The fit in the graph for the first stint requires a pace 0.6s faster than for the second and third stints (identical) using the fuel effect of 0.11s per lap which I derived from the 2011 race by matching stint paces for the same car on the same tyre type/age for different stints and then averaging over the cars. From the opening few laps, it could be argued that the fuel loads are the same in stints 1 and 2 as the blue and red curves match. However, it could also be argued that the second stint is faster – not by enough for it to be purely fuel effect, but by enough to argue that it could be something else like a different tyre compound. The truth? We will probably never know unless they decide to tell us.
The complexity in Rosberg’s trace, however, is somewhat different. Rosberg did four stints, and a comment on the last post has it that the Autosport commentary has all four stints on hard tyres. The timing data I have also suggests that Rosberg did not go into the garage between the first and second stints. The graph of Rosberg’s race is below.
Again the pace is given by the gradients. The dashed line is the mode fit, and the fit for the first two stints is at a pace 1.2s (not 0.6s as I incorrectly stated in the previous post) slower than for the last two stints. It is immediately obvious that the second stint does not follow a typical trace. It looks like two separate stints – a fast pace to start, and a slow pace to finish – neither of which are consistent with the first stint pace. On average, the early pace could have taken more from the tyres resulting in a lower pace at the end. This pace change is usually seen in fuel saving modes in races – the signature on the traces is quite clear, and it is possible that the second half of this stint is a test of a fuel-saving mode. Given that the pace difference between stints 2 and 3 is 1.2s (fuel corrected) and the match from stint 3 to stint 4 is very good, the suggestion that Rosberg refuelled between stints 2 and 3 is probably correct – even though the fuel load at the start of stint 3 would be slightly lower than the load at the start of stint 2 by my reckoning.
I hope that this sheds some more light onto where I get the numbers from, and how I have reached the theories on what the teams have been doing. Of course, all this is speculation, but it I hope that it can give some insight into what is happening in the tests. I’m glad there’s no refuelling in races – it makes it much easier!