What is traction?
Traction is the grip that your car’s tires have on the road, which is needed to accelerate, turn and brake. If your car, or more specifically, your tires have little or no grip; your car will not accelerate, turn or brake and will skid. Therefore, sufficient traction is an extremely important part of the performance and safety of your vehicle. Traction control devices in the car reduce the loss of grip so your tires will have traction to accelerate, turn and brake.
The most common and well-known traction control device is the Anti-Lock Brake System (ABS), which is described in greater detail here.
Traction Control is used to prevent the drive wheels from losing grip when accelerating. Spinning tires during hard acceleration may be dramatic, but it is the slowest way to get to your desired speed. Using the car’s ABS speed sensors at the wheels, the Traction Control computer compares the drive wheel’s speed to the car’s road speed. If there is a loss of grip event during acceleration, there are a number of ways that the Traction Control slows the drive wheels so they can regain grip. The most common method is to use the braking system. When the drive wheels lose grip, the ABS computer can apply the brake to the wheel that has lost grip to slow it down so it can regain grip. Another method for slowing the slipping wheels is to reduce the amount of power applied to them. The computer will electronically modify the amount of fuel entering the engine and/or use the transmission to slow the drive wheels so they can regain grip.
Because Traction Control increases traction by reducing either engine power or applying the brakes, most drag racers turn off their Traction Control Systems (if possible) when drag racing. This allows the vehicle to use all of its available power to move the vehicle forward during the initial launch. A careful launch with minimal wheel spin will lead to faster times that just leaving Traction Control on and stomping the gas. In normal driving, however, you should always leave it on.
The latest traction control technology introduced to motor vehicles is Stability Control. While ABS and Traction Control help manage the grip of the tires for braking and accelerating, Stability Control helps prevent a car from sliding sideways. Using the same components in the ABS and Traction Control systems, Stability Control adds other sensors. These include a steering wheel angle sensor and yaw rate sensor. Yaw is defined as "the movement of an object turning on its vertical axis”. Stability Control is used to manage the amount of understeer a vehicle will exhibit if the driver used too much steering or entering a turn too fast. It will also manage oversteer if the driver uses too much or too little throttle while turning. Much like the other technologies of traction control, Stability Control will apply the brakes and/or throttle to a wheel or a number of wheels, independently, so the driver can regain control.
Modern vehicles, that offer traction control devices, perform a self-test on the ABS, Traction Control and Stability Control computer(s). If there is an error encountered in any of these systems when starting or while driving, an error light will steadily illuminate in the instrument cluster of the vehicle. During this time, one or more of these traction control devices will be unavailable and you should know how to maintain vehicle control if these aids are unavailable.
Since Stability Control is used for maintaining control in turns, most racers leave it on all the time, even for drag racing.