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.

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.

Air density, which is influenced not only by air temperature but by humidity and air pressure, has a big effect on a car’s downforce, which in turn influences the starting ride heights. As an example, the same car going the same speed will generate more downforce in denser air. When conditions are predicted to generate more downforce, engineers will need to raise the starting ride heights of the car in order to compensate (and similarly they can lower the car when air density is predicted to go down).

This is done to keep the car operating at a similar proximity to the ground (where generating downforce is most efficient), no matter the air conditions. A car that is not lowered sufficiently in response to a drop in air density will be too high throughout the lap, losing large amounts of downforce due to operating far from the aerodynamic optimum. A car that is not raised in response to an increase is air density will be lower everywhere on track, which can potentially make the car undrivable. A car that is too low will actually be pushed into the ground by the downforce, called ‘touching’ or ‘bottoming’, when the car is traveling near top speed. Small amounts of bottoming are to be expected as the cars approach top speed, but too much will cause the car to hit the ground so hard that it unloads the tires, which can unsettle the car and cause time loss or even force the driver off the track.

Wind is another aspect that can vary drastically, and since it has a huge aerodynamic effect, it needs to be accounted for in the setup. Anticipating the wind is one of the most difficult aspects of adjusting the setup to get right. Drivers and engineers are constantly kept updated on the current state of the wind speed and direction when working trackside.

Typically, drivers and engineers talk in terms headwind, tailwind, and crosswind relative to various locations on the track. For example, when driving on a straight leading into a high-speed corner, a headwind will do several things: it lowers the car’s top speed, it creates more downforce, and also shifts the aero balance of the car. A tailwind does the opposite of these.

As a consequence, the gear ratios are typically adjusted based on the simulation’s prediction for top speed, which will have to accurately account for the wind. From a performance perspective, selecting gears is a give and take between top speed and acceleration. If a big headwind is predicted then the top gears can be shortened to give better acceleration (since the previous top speed is no longer attainable due to the headwind). In the case of a tailwind, the gears will need to be made longer to gives additional headroom to avoid hitting the rev limiter.

A headwind will also lead to more downforce as there is more air going over the wings, so a ride height compensation will be required to avoid bottoming too hard at the end of the straight. A strong tailwind will have the opposite effect: air going over the wings collides with wind going the opposite direction, and less downforce is generated. The result is a grip reduction, and when a tailwind picks up suddenly it can really catch a driver out. A great example of this was in Turn 2 at last year’s Indy 500. Turn 2 is unique at Indy because it’s the only corner without a massive grandstand to shield the track from the wind. Sudden gusts on corner exit caught more than a few drivers out that day.

Finally, strong winds will change the car’s aero balance, or center of pressure. Aero balance is the distribution of downforce front to rear, so it plays a big part in the whether a car will understeer or oversteer, particularly in highspeed corners. The most common method to adjust aero balance is with the front wing flap. However, since this can only be done between outings or during pit stops, compromises in some corners will have to be made for the benefit of others. When dealing with a big headwind, downforce is added, but it will not do so proportionately front to rear – the wind will change the balance of the car. This can be particularly unnerving because a sudden aero balance shift from a gust of wind (especially when a disproportionate amount of front grip is added compared to rear grip), can cause entry instability and lead to sudden spins because the rear can’t keep up with the front.

Further complicating this matter is that fact that all the corners are oriented differently, so a headwind entering one corner may also be a tailwind or a crosswind for another. To protect from this, engineers sometimes choose to lower the front wing flap angle to give the rear a higher percentage of the overall grip if they think strong winds will make the car unstable. That may compromise the balance in other corners, but it will do so in a stabilizing (read: not crashing) manner.

Summing up

The car is constantly interacting with the track, which means the state of the surface and the ambient conditions will play a huge part in how the car behaves. So powerful is this effect that sometimes teams won’t even venture out if they think the conditions for a practice session aren’t going to be representative to the forecast for qualifying or the race. This is also why the morning warm-up is such an important session for teams, as it is the session where the track surface and ambient conditions are typically most similar to the race. Still, from time to time a race will take place in conditions that haven’t been seen at any point in the weekend, and the teams will simply have to react.

It cannot be overstated how crucial a role simulation plays in reacting accordingly to an ever-changing track. It is pivotal for a team to roll off the truck fast, keep up with a changing track from session to session, and determine the right adjustments (or right amount of adjustment) in order to be successful. Many teams have dedicated Simulation Engineers whose job is to match a mathematical model to reality at the end of a session based on the collected data, then use that model predictively for the subsequent session to determine a best course of action.

Even before the debrief for a session finishes, teams are already looking ahead to potential changes for the next session, especially when the turnaround time is tight during a race weekend. Determining the best setup changes to make between sessions is one of the hardest aspects of a race weekend for the engineers; there are an endless number of changes and combinations of changes that could be done. Ultimately, since the track surface and ambient conditions are the same for everybody during the race, the car setup doesn’t actually need to be perfect, or even good. It just needs to be better than everyone else’s.