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A traction control system (TCS), also known as Anti-Slip Regulation (ASR), is typically (but not necessarily) an electro-hydraulic system on production vehicles designed to prevent loss of traction of the driven road wheels, and therefore maintain the control of the vehicle when excessive throttle is applied by the driver and the condition of the road surface (due to varying factors) is unable to cope with the torque applied. Although similar to electronic stability control (ESC) systems, traction control systems do not have the same goal.

The intervention can consist of one or more of the following:
  • Retard or suppress the spark to one or more cylinder
  • Reduce fuel supply to one or more cylinders
  • Brake one or more wheels
  • Close the throttle, if the vehicle is fitted with drive by wire throttle.
  • In turbo-charged vehicles, the boost control solenoid can be actuated to reduce boost and therefore engine power.

Typically, the traction control system shares the electro-hydraulic brake actuator (but does not use the conventional master cylinder and servo), and the wheel speed sensors with the anti-lock braking system.


The predecessor of modern electronic traction control systems can be found in high-torque, high-power rear-wheel drive cars as a limited slip differential. Limited slip differential is a purely mechanical system that transfers a relatively small amount of power to the non-slipping wheel, it still allows some wheel spin to occur.

In 1971 the Buick division of GM introduced MaxTrac, which used an early computer system to detect rear wheel spin and modulate engine power to those wheels to provide the most traction. A Buick-exclusive at the time, it was an option on all full-size models, including the Riviera, Estate Wagon, Electra 225, Centurion, and popular LeSabre family sedan. Cadillac also introduced the ill fated Traction Monitoring System (TMS) in 1979 on the redesigned Eldorado. It was criticized for its slow reaction time and extremely high failure rate.

Use of traction control

  • In road cars: Traction control has traditionally been a safety feature in high-performance cars, which would otherwise need very sensitive throttle input to keep them from spinning the driven wheels when accelerating, especially in wet, icy or snowy conditions. In recent years, traction control systems have become widely available in non-performance cars, minivans, and light trucks.
  • In race cars: Traction control is used as a performance enhancement, allowing maximum traction under acceleration without wheel spin. When accelerating out of turn, it keeps the tires at the optimum slip ratio.

  • In off road vehicles: Traction control is used instead or in addition to the mechanical limited slip or locking differential. It is often implemented with an electronic limited slip differential, as well as other computerized controls of the engine and transmission. The spinning wheel is slowed down with short applications of brakes, diverting more torque to the non-spinning wheel. This form of traction control has an advantage over a locking differential, as steering and control of a vehicle is easier, so the system can be continuously enabled. It also creates less stress on the drivetrain, which is particularly important to the vehicles with an independent suspension that is generally weaker compared to solid axles. On the other hand, only half of the available torque will be applied to a wheel with traction, compared to a locked differential, and handling is less predictable.

  • In motorsports: it is widely thought that TC removes some skill and control from the driver. As such it is unpopular with many motorsport fans. Some motorsports series have given up trying to outlaw TC. With current state of technology, it is possible to implement TC as a part of software in ECU, and as such it is very hard to detect by scrutineers. Very effective yet small units are also available through a company in the US, Davis Technologies [50313], that allow the driver to remove the traction control system after an event if desired. In Formula One, an effort to ban TC has led to the change of rules for 2008: every car must have a standard (but custom mappable) ECU, issued by FIA, which is relatively basic and does not have TC capabilities. NASCAR suspended a Whelen Modified Tour driver, crew chief, and car owner for one race and disqualified the team after crossing the finish line first in a September 20, 2008 race at Martinsville Speedwaymarker after finding questionable wiring in the ignition system, which can often be used to implement traction control.

Traction control in cornering

Traction control is not just used for moving a vehicle from stationary without slippage. During hard maneuvers in a front-wheel drive car, there is a point where the wheels cannot both steer and drive the car at the same time without losing traction. With traction control, it's less likely for this loss of control to occur. There is a limit though, when the tires lose grip. If the car does not corner as sharply as indicated by the front wheels, understeering occurs. In some front-wheel drive cars, traction control can induce lift-off oversteering due to its throttle retarding capabilities. This can keep some cars stable in long maneuvers. In rear wheel drive cars, traction control can prevent oversteering.

Automobile manufacturers state in vehicle manuals that traction control systems should not encourage dangerous driving or encourage driving in conditions beyond the drivers' control.


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