2. Getting off the inferior race tire

IndyCar rules mandate that each car run both tire compounds in a dry race, and as a consequence both tires will always be compared to each other over the course of a full race stint to determine which one is preferred. Sometimes, the difference in tire performance will be so great that teams will choose to spend as little time on one of the compounds as possible. This usually involves starting on the inferior tire, pitting very early to get off it, and then running longer stints on the superior tire until the end of the race. Doing so has a domino effect on fuel strategy: if the first pit stop is made early, the team will have to save fuel for the rest of the race in order to lengthen the subsequent stints and avoid an additional pit stop.

Going back to the 100 lap race example, now the Alternate tire is modeled as a really poor race tire this weekend. Yes, it’s 1.0s faster at the start of the stint, but it wears so badly that pretty soon the driver is on the radio saying the tires are dead. Going with the flat-out approach would mean doing 25 lap stints, going Alternate/Primary/Primary/Primary. It’s nice because there’s no fuel saving and the driver can push the whole time, but when the Alternate tire wears badly, 25 laps is a long way to go, so maybe it’s not the fastest strategy for this race.

Stopping on lap 22 would get the Alternates off a bit earlier, and then three 26-lap stints on Primary tires would follow in order to get to the end. It would require a bit of fuel saving (to get an extra lap on each of the final three stints, the consumption would only have to go from 0.74 gallons per lap to 0.71), but it would mean three less laps on worn Alternate tires.

This idea can be taken further by stopping on lap 19, then doing three 27 lap stints at 0.685 gallons per lap. And from this, a pattern begins to emerge. The earlier a team gets off the inferior tire, the more they have to fuel save for the remaining stints on the superior tire. And so it becomes a balance between tire life and fuel saving pace. At what point is this trade-off no longer worth it?

Turning back to the race simulation model, it will now also consider the Alternates, which can do a 59s lap and degrade at 0.2s per lap. From practicing fuel saving in one of the warm-up sessions, the team knows that extending a stint one additional lap means running at a pace 0.03s slower for the whole stint: so a 26-lap Primary tire stint is run at 60.03s (plus deg) in order to hit the fuel target, a 27 lap Primary tire stint is run at 60.06s (plus deg) in order to hit the fuel target, and so on. Armed with this information, teams can begin to sweep through all the possibilities of when to take off the Alternates, and then calculate the how the remainder of the race would go.

When graphed, it really highlights just how punishing it is to stay on the Alternates tires for too long (green plot). It’s true that staying out longer means less fuel saving for the rest of the race, but sometimes that’s not enough to make up the for the time lost by staying out on too long in the beginning. The green trace (which pits on lap 25) emerges from the first round of stops in last place, and even though no fuel saving is needed from that point onwards, they only make up one spot (passing the yellow trace with eight laps to go).

It’s also evident how the difference in degradation between Alternates and Primaries plays a huge role in determining pit laps and fuel targets. In this example, the optimum first pit stop is lap 16. That’s a whole nine laps earlier than the no-fuel-save strategy, and it’s 7.74s faster. For any race that is a huge difference, all born out of strategy options that are only possible thanks to fuel saving.

Throughout the season, the preferred pit stop lap will change depending on the performance difference between the compounds and the time loss when hitting the fuel target. These factors can vary from track to track, so teams are constantly using practice sessions to gather this data.

As the model continues to gets more sophisticated, some may wonder why team don’t simply calculate the optimum strategy and do it every race. In reality, there isn’t always a consensus on what is the best strategy. Every team is using their own tools and their own data, drawing conclusions from their own analysis and experiences. Sometimes teams just have different opinions on what they think is best. There are countless examples of teams just getting the strategy downright wrong, whether it’s the number of stops or which tire is preferred. Other times, the data collected in practice isn’t fully representative of the race. In the example, the race started with the team thinking the Alternates would degrade at 0.20s per lap based on practice data, but oftentimes the ambient conditions are much different for the race. If it gets to lap 13 and calculating the degradation says it’s more like 0.35s per lap, the optimum lap to stop on is lap 10 – but it’s too late to do that now!

No strategy is so stagnant that it is decided before the race and then simply followed like an instruction manual. Information throughout the race regarding deg, fuel targets, cautions, and traffic all evolves in live time and the teams need to react accordingly.

Another reason that there is not one single strategy is because the optimum strategy is different for each team. Even at the very top level, there is a wide spread on several important factors, such as a setup’s effect on tire deg, a driver’s ability to fuel save and not lose lap time, or the amount of traffic a team will have based on their starting position. These will change what the ‘best’ strategy is for each team for their situation. Traffic plays a huge part in strategy decisions, since being stuck behind another car can affect pace drastically. If a model says the three-stop strategy is faster because the pace warrants the additional pit stop, that model better consider the fact that pitting an additional time will mean being behind cars and losing time while trying to pass them.

3. The undercut

Since traffic can be so detrimental, teams turn to a strategic move called the undercut, where they will intentionally stop earlier than what the model says is ‘ideal’ in order to avoid traffic. Think of an undercut as an advance loan on pace: the team gets to go to new tires earlier and push in clean air, but will have to reduce fuel consumption later on in the stint to make up for having stopped earlier. Still, if the time gained through the pit cycle allows the team to get past a car they otherwise wouldn’t be able to overtake on track, the benefit can be massive.

In the previous example, the model said the optimum pit stop lap was on 16, but stopping on lap 15 would make total race time is only 0.36s slower, which admittedly is not that much compared to the loss that can be caused by traffic. Being behind a car that is running 1.0s slower that they can’t overtake because of dirty air can ruin the entire race. So the faster car that is stuck in traffic decides to pit on lap 15, one lap earlier than optimum according to the model. By the time the slower car decides to pit on the optimum lap, the faster car has gained enough time comparatively in clean air that the slower car comes out of the pits behind. Now in front, the superior pace allows the faster car to pull away despite having to save more fuel in order to go one lap longer on this stint.

Undercuts can be used offensively as just shown, or defensively. There’s nothing to stop the slower car in front from pitting a lap earlier and doing the exact same thing in order to keep the position. Yes, the car in front is now slower and saving more fuel, but if the quicker car still cannot get past, the tactic has successfully maintained position.

This is a critical decision in-race that is really difficult to model. If both teams are trying to undercut each other, a game of one-upmanship can ensue, leaving both cars pitting absurdly early just to cover each other and having to drastically reduce their consumption. While this may do well to keep them in front of the car they’re battling directly, this could leave the team vulnerable to other cars. While models are good at considering factors intrinsic to the team itself (compounds, number of stops, deg), determining the actions of other cars in the race is very difficult to predict.

Final thoughts

These are just some of the many ways in which saving fuel can give teams a strategic advantage as the race plays out. While teams are always looking for ‘on-car’ performance, a team’s ability to predict and numerically model all the considerations that go into choosing a strategy is equally as important. Being the best fuel-saver in the world doesn’t win much when it’s done at the wrong times. Still, as with anything in IndyCar, if there is a performance benefit to be had then teams will do everything in their power (and budget) to maximize it. Teams will go to great lengths to be better at saving fuel than their rivals, as these have examples have shown it can play a huge part in finishing ahead.