IndyCar tech download: Taming the track

Michael Levitt/Motorsport Images Why do black lines lead to a terminal point and the other line leads to winning the race?
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emailBy Stan Sandoval | April 11, 2023 4:11 PM ET

The IndyCar calendar offers what is probably the most diverse collection of tracks of any racing series in the world. This is usually taken to mean that over a season, IndyCar pays visits to the likes of speedways, short ovals, road courses, and street courses. However, the variability in surface type, bumpiness, grip level, and ambient conditions that IndyCar teams will experience over the course of a season is also extraordinarily diverse, and something that engineers are constantly analyzing and assessing as they fine-tune setups in search of every ounce of performance.

Unlike every other sport, in racing each team is not only battling with one another but also with the field of play itself, and that arena changes from week to week (and even session to session) in ways that no other sport would allow. While the likes of soccer, football, and baseball have standardized their playing surfaces – and even gone so far as to play indoors under stadium roofs to protect from outside conditions – teams in racing are left to adapt on the fly to the ever-changing characteristics of the race track.

Engineers are almost always thought of as engineering the car, but there times when a better way to think about it might be that they are trying to reverse-engineer the track, and simply apply the appropriate changes to the car as a result.

Teams and engineers are constantly adjusting a whole host of setup parameters in reaction and anticipation to track surface and ambient conditions changes that occur throughout a race weekend. Being able to adapt (and even predict) these changes offers a huge competitive advantage to those that can continuously keep the car’s setup in the optimum window, even as the variables are changing all around them.

The track surface

The joke that is made wherever race car engineering is taught is that the four most important parts of a race car are the tire, the tire, the tire, and the tire. It’s a saying based on truth: the importance of the tires is no joke, they are the only part of the race car that actually comes into contact with the road. By extension, the most important part of the race track is the surface, for largely the same reason. The state of the racing surface is the dominant factor in the amount of available grip for the tires in a given session, lap, or even corner.

Track temperature is the single biggest consideration when assessing the surface. Tires have an operating window where they produce the most grip: too cold and the rubber doesn’t get sticky, too hot and the tire will oversaturate and begin to slide. Given the relationship between a tire’s pressure and temperature, engineers are constantly adjusting the starting tire pressures based on track temperature in order to keep the tire in its operating window.

Track temperature is hugely influential on tire pressure and temperature, and therefore its effect on overall grip is very powerful. The track grip, usually quantified as a friction coefficient, then dictates practically every aspect of a setup: from downforce level to spring stiffnesses to static alignments to gearing. Put simply, a car setup exists to take advantage of the available track grip at all times if possible, or make the best compromise for overall lap time if not.

Not only does track temperature dictate the grip level, but also the car balance. Since the front and rear tires are different widths, have different forces acting on them, and are used in different ways, a change in track temperature does not have an equal effect on the front tires as the rears. A sudden shift in track temperature will not only change the grip level, but also the understeer or oversteer characteristics of the car. As track temperature itself is constantly changing, an engineer’s job of dialing in a setup is a never-ending task.
Street courses often serve up different surfaces on different parts of the lap, forcing engineers to hunt for a compromise. Phillip Abbott/Motorsport Images

The road material is another factor influencing grip, because that is what has to interact with rubber of the tire. Different types and ages of asphalts, tarmacs, concretes, and sometimes resins are seen over the course of an IndyCar season, and each offers slightly differing amounts of grip. This isn’t so much an issue when the track is one uniform surface, but tracks like Toronto famously use different materials in different corners. In this case, engineers simply have to make more compromises: a setup change that might benefit one corner but hurt another.

Road material is also a big reason why teams go test at tracks after they’ve been repaved. Barber Motorsports Park was completely repaved in late 2019, and because of this there was an enormous increase in grip. Testing in early 2021 was important: laps were more than 2.0s faster than the pole time from 2019 (and that’s despite the addition of the aeroscreen). Such a big difference required not only a rethink on setup, but a completely new stack on gears given the difference in cornering speeds.

Track surfaces can also vary wildly in terms of bumpiness. A lap around Detroit is a very different experience compared to a lap around Barber in this regard. The primary effect of bumps on setup is the spring and damper package. Stiffer cars can be run lower to the ground, which is good for downforce, and are more reactive and better at changing direction. However, stiff cars do not handle bumps well at all. The ability of a softer setup to absorb the bumps and keep the tires on the ground is critical; the tire can’t do anything if it’s not on the track because it’s bouncing up in the air!

Finally, when analyzing the track surface, another vital factor is ‘track evolution,’ or the amount of rubber that’s been put down. To start a race weekend (or after a rain shower), the track is referred to as “green,” meaning a fresh track. As cars beginning completing laps, they will leave a layer of rubber down on the track. The more laps that are run, the more rubber there is on the surface. This beneficial for grip: the best thing that rubber can stick to is more rubber, so the more laps that are run on a track, the faster it gets. This why it’s called ‘track evolution’, and it’s the reason teams typically wait before they start running at the beginning of the first practice, and why teams will always try to leave their qualifying laps as late as possible. Like many of the other factors discussed already, as track grip changes so does the balance, and so engineers will have to compensate accordingly with the setup.

Teams will always try to stay ahead of track evolution because it is relatively predictable. However, a quirk of putting rubber down is that the calculation changes depending on what kind of rubber was put down most recently. Different tire compounds don’t always agree with one another. Engineers will always take note of what series ran on track immediately before a session, as a race weekend typically has many series competing one after another. If for example, a NASCAR session ran immediately before an IndyCar session, engineers would expect the grip to be slightly reduced to start the session, because NASCAR rubber doesn’t aid track evolution for an IndyCar.

Another aspect of track evolution is marbles. If you’ve ever taken an eraser to a piece of paper and seen bits of rubber chunks fall off, then you’ll be familiar with the concept. As tires are grated against the track surface, the worn rubber is shed from the tire and lands off the racing line. Driving on the marbles is a massive grip loss and can be very treacherous; they get between the tire and track surface, like a cartoon character trying to run on ball bearings.

Ambient conditions

As IndyCar races everywhere from Florida to Oregon over a seven-month period, naturally a wide range of temperatures, air conditions, and wind will be encountered during the year. Changes in these conditions will have knock-on effects to the car’s setup that are vital to get right: a team’s ability to adjust their setups as conditions changes can be the difference between having a competitive setup or a poor balance by the time the race comes around.

Changes in air temperature will affect several aspects of car setup. The importance of track temperature has already been discussed, but track temperature is heavily influenced by air temperature and cloud cover. The radiator covers, sometimes called blockers or blanking, come in various sizes and are largely dictated by air temperature. These covers can be seen at the inlet of the side pod, and their shapes differ depending on the engine manufacturer. Covering more of the radiator is beneficial for drag, but also leads to higher oil and water temperatures for the engine, which affects power output. Finding the right compromise of drag, power, and reliability by adjusting these blockers depending on the air temperature can have a huge impact on performance, especially at aero-sensitive tracks like Indianapolis Motor Speedway, where drag and power are the dominant factors on lap time.