Tricks of the trade in IndyCar fuel saving

Gavin Baker/Motorsport Images
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emailBy Stan Sandoval | January 19, 2023 10:34 AM ET

Optimizing for lap time

The idea of simulating potential fuel saving approaches can be expanded from a basic example of just one straight to simulating an entire lap, but doing so brings additional complexity. Distributing where the driver lifts and coasts throughout the lap increases the number of simulations by several orders of magnitude. Putting aside engine modes for this example, say that at a (fictional) street course with five corners, a push lap burns 0.742 gallons and the fuel target is 0.668 gallons (or 10% reduction in consumption). Now, the driver wants to know where the best places to lift are and how much should they be lifting in each corner. Is it faster to only do one big, long lift on one straight to save the entire 0.074 gallons in one go? Or should the driver do smaller, shorter lifts throughout the lap adding up to 0.074 gallons saved in total? Once again, lap time simulation is an engineer’s best friend. These simulations can run hundreds of thousands of laps at the click of a button, and then data analysis software can immediately point to the best solutions. Below is a typical sweep of various lift and coast distances for each corner of the track.

Move your cursor over the graphs to reveal additional details



After using lap time simulation to create this data, finding the combination of lift and coast distances in each corner that can stay under the fuel target while also going the fastest is now a straightforward data analysis problem. Code can be written to create theoretical laps for every combination of lift and coast distance in every corner (that’s 16,807 laps in this example!), and the fastest approach that hits the fuel target will become apparent. In this sweep, the engine mode has been fixed and only one fuel target has been given. But in reality, both of those parameters are also variable during the race and so the amount of pre-event simulation done by the teams and manufacturers in the weeks building up to a race weekend can become enormous, as they have to be prepared for all possible scenarios.



The simulations say that when fuel consumption is reduced by 10%, the lap time loss can be anywhere from 0.121s when done optimally to 1.678s if done inefficiently. Since fuel saving simulations like this are so important and are used week-in and week-out, teams have typically developed software and code to automate these tasks to immediately solve for an ideal approach.

Also from these results, something else that has already been touched on (but can now be seen in the data) is that the higher the entry speed, the better suited that corner is for lift and coast. From this, it follows that the fuel saving characteristics of each track are different from one another. Tracks with long straights and big braking zones (like Nashville) tend to be more suited for lift and coast, whereas tracks with shorter straights and flowing corners (like Barber) tend to prefer using engine modes.

Traffic and track position also plays a big factor in how teams save fuel throughout the race. Thus far, fuel saving has only been discussed through the lens of optimizing lap time. But for a track like Nashville, the end of the two long straights are also great overtaking spots. If a driver needs to save fuel but also defend their track position, a big lift and coast at the end of each straight leaves them vulnerable to being passed. In these situations, drivers will do their fuel saving in parts of the track where overtaking is impossible, like the back section of Nashville from T4 to T7. While this certainly isn’t ideal for lap time, it does allow the driver to hit the fuel target while giving them the best chance of maintaining position. The optimum fuel save approach will always depend on how much fuel needs to be saved, but the characteristics of the track and traffic are just more variables for drivers and engineers to consider as they hone in on a best solution.

The driver

A deeper look at these overlays can also begin to show why resorting to lift and coast requires a change in driving style, and why some drivers are better at it than others. Adding a lift at the end of the straight obviously lowers the entry speed compared to pushing at 100%, so drivers can actually brake later when doing lift and coast and still achieve the same apex speed. This means that braking is done over a much shorter distance when saving fuel, which changes the required peak brake pressure and the bleed-off technique that should be used. Because there is only a finite amount of tire grip to be allocated for both braking and turning, the knock-on effect of changing braking technique is that the steering technique to rotate the car on entry changes as well.
The most effective drivers are able to stretch their fuel with virtually no penalty to their lap time. Joe Skibinski/Penske Entertainment