Estimating FP2 Long Run Fuel Loads

In Friday Free Practice 2, the teams will send their drivers out to do a simulation of a race stint to get a better idea of how far and how fast they can go with the tyres on Sunday.

You’ll probably hear your commentary team raving on about Ferrari’s competitive long-run pace to build hype for a close race on Sunday but Mercedes are (almost) always in total control. After Austria’s FP2 session, Ferrari looked stronger than ever this season, for once, I thought they could’ve won the race. Kimi’s long run was longer, and averagely faster by 0.2s than Rosberg’s… and we hadn’t seen what Sebastian could do yet. But thanks to slower pace in the first stint and a disaster of a pit-stop for Vettel, the SF-15T finished 18 seconds off the lead, and behind a Williams too.

I’ve noticed that in recent races that the Mercedes gains around 0.5s advantage relative to the Ferrari going from FP2 heavy fuel pace to Race pace, but with a short laptime of around 70 seconds, the gap would likely be less at the Red Bull Ring.

We can calculate the fuel loads the teams run on Friday by analysing them against the race laptimes in Austria, but there were small changes in track grip and driver effort which we can’t measure so really these are more like rough estimates. But let’s proceed:

Mercedes

I’ve tried to make these graphs easy to read. The red and yellow dots follow the Pirelli tyre colour coding and the dashed line shows the times were from the practice session. The laptimes in the first stint do not include the ones behind the safety car as a result of the Alonso/Raikkonen incident. We have used Rosberg, not Lewis here as his alternate FP2 run was only 5 or so laps, and wouldn’t have made for a good comparison.

As you can see the prime tyre laptimes were a lot faster than in FP2 however the stint did start on lap 33 of the race and the weight of the unused fuel in the car would would be considerably less. I have obtained some values for fuel time cost per kg online for the Red Bull Ring and the fuel weight cost per lap is roughly (100kg ÷ #Laps in the race). This assumes that all drivers start with 100kg and distribute their fuel use equally – which is not true for both assumptions, so I’m going to be a little off.

Through the values of fuel consumption and fuel weight cost, I could find out the difference in fuel between lap 1 and lap 35 – Nico’s first flying lap after the pitstop. And compensate for this weight reduction by adding in the time.

Although both sets of results are a little varied, I think you’ll agree that the best matching race pace is the line with has been fuel adjusted to 80kg. So this indicates Mercedes filled their car to 80kg for their FP2 long run. Let’s see how this compares when we do the same for Ferrari:

Ferrari

Admittedly, I have to use different drivers for Ferrari which is not ideal. This is because Vettel’s FP2 run was of similar use Lewis’, and Raikkonen didn’t really have a race to analyse, and it would’ve been in traffic…

…but even so, we can see once fuel adjusted, it appears Ferrari run a load of around 75kg of fuel in FP2, which I was hoping for, because it is less than Mercedes. Notice how the times climb at the end of the stint, however this is because he caught up with Felipe Massa in the fight for third.

Vettel pitted a few laps after Rosberg so I have changed the fuel compensation accordingly.

The time cost of having a heavier car at the Red Bull Ring is surprisingly high for such a short track at approximately 0.04 (0.0398) seconds per kg when the average across the calendar is more like 0.03 seconds. So the difference between having 80 and 70kg of fuel is 0.398 seconds, which goes some way to solving why the Ferrari was 0.2s/lap faster on Friday and 0.4s/lap slower on Sunday.

The other 0.202 seconds could come from Sunday’s warmer temperatures suiting Mercedes more, Mercedes going more aggressive with settings to defend or some other factors.

Williams

Over to Massa now and his robotic consistency. Unlike Rosberg and Raikkonen, Massa’s FP2 run was done on the Option tyre and we don’t need a second graph to see that his first stint of the race on the same compound was very similar. The degredation on the prime tyre was also very impressive. His tyre degradation curve never accelerated enough to overcome the laptime reduced by fuel-use until maybe the last few laps of the race.

We can deduce from this that Williams start the race with similar fuel to their FP2 long run. Williams tend to use less fuel and are looking to improve their efficiency further with Petrobras, so I estimate this figure to be roughly 95kg. This would be a good reason why, in FP2, Massa wasn’t much faster, if at all, (Visible on very top graph) than Raikkonen in their long runs, despite being on the faster tyre. A difference of 20kg is around 0.8 seconds here.

Conclusions

– When looking at FP2 long runs, imagine Mercedes are 0.4 seconds faster relative to Ferrari…

– …and imagine Williams are 0.8 seconds faster relative to Ferrari to give a better indication of race pace.

– Or follow the same time ratio for different tracks as you can find on this graph: Remember this is just the analysis of a single weekend and will definitely vary from others. Hopefully this will suffice for now.

Thank you for reading.