Right height and aero balance is one of the first adjustments we make after setting the tyre pressures. It is important to acknowledge the demands of track we are creating the setup the car. For example, Circuit des 24 Heures du Mans has loads of straight aways which we would want a low downforce setup with almost a neutral rake for minimum drag and therefore more top end speeds. On the other hand, a track like Silverstone requires a high downforce since most of the corners are high speed. Lets dive into the physics behind the car’s ride height first and then move on to aerodynamics.
Setting the optimal ride height of a car most of the times we want to bring the car as low as possible to the ground to create a low center of gravity. By having a low center of gravity, we can carry more speed into the corner as the car does not roll as much. Therefore, in most cases we go for the lowest possible settings on ride height. On the iRacing simulator the ride height adjustments are usually done by changing the Spring Perch Offset value for each wheel.
Spring Perch Offset
For cars with coil-over spring/damper units, the spring perch offset is the distance from the spring seat of the spring perch on the shock body to the rod end of the shock body. Decreasing the offset will raise the car up and increasing the offset will lower the car.
We must keep in mind that the spring perch offset adjustments have an effect on other areas of the suspension and the aero balance. Here is a list of areas that are affected with the changes:
- Camber & Toe (You will notice that when you change the spring perch offset, the camber and toe of the car will change. Make sure to keep an eye on the camber and toe values before you make the spring perch adjustments and set them at that value after the change to ensure that you are just changing the ride height and not anything else)
- Downforce & Drag (This is affected as with more rake which is covered next, you get more drag but more downforce as well since the front of the car is lower than the rear of the car)
Rake is the term used to describe the difference between the front and rear ride height of the car. A positive rake is when the front suspension is lower than the rear which is what we are aiming for when setting up the car. Having a bigger rake tends to make the car have less understeer since we are loading up the front tyres more thus improving the front end grip. In addition, having more rake will increase the downforce of the car and the amount of drag. Keep in mind that in some cases a bigger positive rake will cause snap oversteer as the car’s rear end does not keep up with the front since the load at the rear is less. Below you can find what effects the changes in spring perch offset have:
It is important to know that there are some factors that affect the ride height of the car besides the spring perch offset. You can find the list below:
- Fuel (Adding for fuel to the car will decrease the ride height as we add more weight to the car and vice versa)
- Tyre pressures (Increasing tyre pressures will raise the car since more tyre pressure makes the tyre expand and vice versa)
- Spring Rates (Stiffening the spring rates will raise the car and vice versa)
- Camber & Toe (As already mentioned, ride height affects camber & toe and making changes to camber and/or toe will affect the ride height as well)
Getting the right aero-balance for a car in a certain track is very crucial although sometimes the amount of downforce is a driver preference as some drivers prefer a higher top end speed where others prefer a higher cornering speed. We can change the amount of downforce and drag of the car by changing the value of the wing angles.
Wing angles are one of the adjustments that are different from the other handling adjustments. Some cars on iRacing don’t have any wing angle changes because the aero package is standard and cannot be changed where as others have extremely sophisticated aero settings such as an LMP1 car or the MP4-30. Increasing the wing angles adds load on the tyres which results in increased cornering speed and better acceleration without compromising the weight of the car. The more downforce that we have in a car, the more drag we generate therefore, top end speed decreases.
Below you can find the effects of changing the wing angles at the front and the rear cause:
The Audi R8 LMS always uses max wing.