part 2 taming the track
Hitting on the right configuration for the radiator blockers can make a massive difference at aero-sensitive tracks like IMS. Michael Levitt/Motorsport Images
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.