Caster

Not all cars on iRacing support caster changes. For example, the newer GT3 cars don't support this, while older GT3 cars do. It is a shame as caster can be a powerful tuning aid.

The biggest advantage of adding more caster is that you can run less static camber on your front wheels and thus gain some more braking power, because caster will dynamically increase your front camber when you turn the wheel.

If you were to draw a line through the two points (bottom and top) at which you attach the hub on your car this line defines the Caster of your car. The top attachment point is typically closer to the rear of the car than the bottom attachment point, giving you a line that leans towards the back of the car from bottom to top as shown in the following diagram.

Caster helps the car Self Center

The more degrees of caster you run the more the car will self-center itself while driving in a straight line. This is because the side forces acting on the wheel have more leverage the further the wheel is behind the bottom connecting point (shown as the Trail Distance in the following figure) of the c-hub.

Caster changes the Camber Dynamically of the front wheels as your turn.

As you turn the front wheels during cornering the angle of the caster affects the angle of the camber dynamically. As you turn the front wheels, the caster causes the camber to increase negatively on the outside wheel and decrease on the inside wheel. In fact, the inside wheel often will end up with a positive camber. The greater the caster angle the greater the effect it has on the dynamic camber change. The more you turn the wheel the greater effect the caster has on the dynamic camber.

How does it affect the handling

More caster typically increases mid corner steering: This is because at mid corner the car has fully rolled into the corner allowing the dynamically increased negative camber to increase the contact patch size generating more lateral grip. However, too much caster is like having too much static negative camber, which can reduce grip because your tire goes past the optimal angle and actually reduces the contact patch,

More Caster also decreases initial turn-in: This is because it decreases the contact patch on initial turn-in by adding some dynamic negative camber before the car has time to roll into the corner.

Improves Braking: When you run caster you can reduce your front static negative camber, which keeps the front tires flatter and thus have a larger contact patch under braking. As indicated in the Camber section, most setups will run less front camber than the rear, because the caster adds negative camber as you turn the car.

Handling Scenarios

In each of the following scenarios, here are things you will help you improve the handling by making changes to caster. You don't need to do all of the suggested changes listed below in these scenarios. It is best to start at the top of the list and do one at a time.

Loose Off Power

• reduce caster

Loose On Power

• reduce caster

Push Off Power

• Increase Caster

Push On Power

• increase caster