Get the perfect fuel calculation, every time with this advanced guide!

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There are currently many basic fuel calculators, for example, the one we have on PitSkill.io that’s perfect for shorter races or single stints, but especially for longer races, you might need something more advanced to ensure you put the exact amount of fuel you need.

Knowing how long and how many stints you will have is crucial. Depending on the settings, there might be more than one optimal strategy. You should be aware of them and either decide on one before the race or leave your options open.

grafik

You need to consider the race length as well as the possible mandatory pitstops and their requirements: (fixed time) refuelling, tyre change, and driver change. There can also be a maximum stint time that will limit how long you can drive before going through the pits, as well as a maximum driving time in case of team races. All these factors influence the valid strategies for a race, so analyze them all and try to figure out which ones are the fastest.

The theoretical way to approach it is to make a (mental) list of all possible combinations and try to calculate which one would make you finish the race with the lowest average lap time. With some experience, you’ll recognize the winning strategies at once, but in others, you would really need to put in some thought and calculations. If you want, you can use the Spreadsheet I created to precisely calculate the fuel you will need in any race.

Let’s use the following race settings as an example for the next steps:

Race duration: 90min
Rules: Mandatory PitStop with refuelling
Track: Spa-Francorchamps (dry conditions)

In this case, even without a pitstop, you would very probably need to pit for fuel unless you do heavy fuel saving with a car like Bentley. However, it remains open if you want to change tyres, and therefore save a good amount of time (you would only stop for the refuelling time). It is important to check how much fuel you need in total for the race, and how much refuelling time you will have. Subtract that refuelling time from the 30s and that’s the time you would gain with that strategy.

Calculate the number of race laps:

This calculation is probably the most important and the one most people don’t get right. In order to know how much fuel you need, you have to calculate how many race laps will be done; this is not the laps you are able to do with your pace, but the laps that you estimate that P1 can do.

A reminder, Spa is a very special track and the only one where the start of the race is not the finish line. This means you can add like the 20s to the race duration for the purpose of the calculations. Let’s put some numbers to the formulas:

P1 pace: 2:18 (138s)
Time lost in pits, only refuel: around 70s
Laps: (90*60 + 20 – 70)/138 = 38,7681 –> always round up!

This means the leader will complete 39 laps during their race if no incident happens. Actually, you can also calculate the minimum average pace of the leader to complete the 39 laps:

Min_avg_39: (90*60 + 20 – 70)/38 = 140,7895

So, as long as the leader maintains an average pace faster than 2:20.7, they will cross the line on lap 38 before the clock reaches 0, forcing another lap.

Let’s see what the average pace should be in order to actually complete 40 laps:

Min_avg_40: (90*60 + 20 – 70)/39 = 137,1795

An average lap time of 2:17.1 seems rather unrealistic, especially without changing tyres. So we can discard this one.

After doing these calculations we can be sure that we need fuel for 39 laps (+1 extra for the formation lap). If the consumption is 4l/lap, that means 160l in total. Let’s say the tank size of your car is 110l, that would mean you need to refuel 50l. You can check how much pitstop time that means by setting this refuelling in practice and unchecking the tyre change.

As a rough estimate, I’d say this is something around 13s, so you would gain 17s by not changing tyres.

Looks like a great deal, right? Well, bear in mind you will be 90min with the same tyres, whereas changing them would mean something like 2 stints of 45min each. The question is, could you make up for these 17s by having fresher tyres and around 30l less fuel during the first stint? You should be at least 17/39 = 0,4359s faster per lap on average with the tyre-changing strategy to make it work. Actually even more, because by changing tyres you will lose track position to other cars not changing them. This is a decision to take based on risks, assessment of your rivals, track conditions, tyre degradation and many other factors, but we’ll leave this to another post.

We hope you’ve enjoyed this post, leave a comment below if you’d like to hear more about strategies, or what you’d like to see a post on next!

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