TIRES

Would you like to try our cool Tire Editor?

Racecars have to travel through the air, and over a surface. Since aerodynamics affect how the car moves through the air, tires are the main factor in how the car travels over the surface. Everything the driver feels and every action the driver takes to control the car goes through the tires. Basically, you can simplify the importance of tires this way: the better the grip, the better your car will react. That is why aerodynamics and tires are so co-dependent. Much of aerodynamics is focused on increasing downforce, which creates more weight on the car and gives the tires better grip.

A vehicle turning a corner is actually accelerating towards the center of the arc of its path. The cornering force that tires generate is called the lateral force or side force. A tire can't produce the lateral force needed to turn the car without slipping. The slip angle is the angle between where the tire is pointed and where the car is actually going. The tire tread actually deforms as it rotates through the contact patch area and then recovers as the car's weight comes off the contact patch. The force needed to deform the tire is what produces the lateral force needed to change the path of the car.

TIRE TEMPERATURE
Just about everything that you adjust on your tire will affect the tire temperature. Tire temperature greatly affects the durability of your tires. If your tires get too hot, the rubber starts melting off, and your tires loose grip. You generally want to distribute weight evenly across all the tires, so that heat is distributed evenly. Localized heat can wear tires down much quicker which may force you to go into pitstops more often. Getting tires to the right temperature can greatly increase grip. This is why when you start off in a race with cold tires, your grip is moderate. As you race a bit, tire temperature increases and so does tire grip. However, once the temperature gets too high, usually after about a couple of laps, you start to notice weaker handling capabilities. Expert racers can use this to their advantage in devising strategies to out-maneuver their opponents.

TIRE SIZE (width)
The width of the tire affects the handling of the car. Generally speaking, the wider the tires, the more contact it has on the road, the better the tire grip. This gives the car better handling capabilities. However, wider tires have increased rolling and aerodynamic drag which slow the car down.

TIP: Using a wider set of tires on the rear of a car has a few advantages. Rear tires have less of an aerodynamic affect. Rear tires (generally) are required to provide more force, more often than are the front tires since the rear tires are the ones accelerating the car out of a corner.

TIRE PRESSURE
This is simply how much air you have in your tire. The pressure is used to make adjustments to compensate for tire temperature or to add small amounts of understeer or oversteer. The tire pressure's affect on rolling drag and grip are minor.

Because tires can also act as spring/dampers, the tire pressure can affect the spring rate of the tire. Inflation pressure changes the spring rate of the tire much more than camber. Thus small changes in inflation pressure make a big difference in how a car handles.

TIP: If there is too much air in the tires which makes it less absorbent to bumps, car handling decreases, and the likelihood of a driver losing control of the car increases.

CAMBER
The camber is the measure of the tilt of a tire when viewed from the rear. Camber is used to adjust the tire so that the maximum tire tread is in contact with the ground when cornering. Camber has dramatic affect on rolling drag and tire temperature.

One of the reasons you see racecars setup with a lot of negative camber is that tires produce camber thrust, which adds to lateral force. When you make a hard turn, the force of the turn makes your car angle out. With negative camber, when your car makes that turn, the grip on the tires ends up with the maximum contact with the ground because of the tire warping. Suddenly, your car has greater grip which results in you taking the corner at faster speeds, and increased acceleration out of the corner.

Note that camber has dramatic affect on tire temperature though. You don't want the tire running on its inside corner too much because you're not using all of the available tread, and local heat buildup can degrade tire performance. For courses with few hard corners, you want zero camber.

TOE
The toe affects the steer characteristics of the car. Typically, the toe is set near zero degrees. Increasing toe can add a small amount of built-in steer and can be adjusted to help the tires maintain an ideal temperature range.

STAGGER
Stagger is the vertical size difference between the left and right side tires. Making one side bigger makes the car automatically turn a little. The effect is demonstrated in the picture. This is mostly useful on oval tracks where you're always turning the same direction.

RAIN TIRES VS DRY TIRES
Rain tire compounds are optimized for wet grip, and depend on wet weather to keep cool. They deteriorate quickly at higher temperatures. Dry tires are useless in the rain because they allow a layer of water (a good lubricant) to form between the road and the tire. Rain tires are, more or less, dry tires with grooves cut in them. Some race teams actually prefer to groove their own tires or modify the tire company's stock rain tire with their own groove pattern. Still, the wet roads will result is more dangerous driving conditions even with rain tires, so overall speed and cornering should be taken more cautiously.
NOTE: Rain or Dry tires are automatically selected by XCar, depending on the current track conditions.