Why Electronic Drivers' Aids & AWD/4WD Systems Aren't Enough for All Seasons(Lea en español)
Anti-Lock Brake (ABS), Traction Control and Vehicle Stability Systems
Anti-lock brakes, traction control and vehicle stability systems help make it easier to utilize a tire's full potential; however, none of these systems actually generate more traction. For that matter, they only begin to work after onboard sensors identify the driving conditions and the driver's input will potentially cause the vehicle to exceed the tire's ability to provide traction.
Tires maximize the effectiveness of these systems. Here's how:
- Anti-lock braking systems help prevent skidding during panic stops by monitoring how fast the wheels are rolling and selectively releasing pressure and pumping the brakes if wheel lockup is detected. So while anti-lock brake systems help maintain steering control and directional stability, vehicle stopping distances may be longer. Only the tires provide traction when stopping.
- Traction control helps prevent spinning the tires during acceleration that's too aggressive for the road or weather conditions by reducing the engine's power and/or applying the brakes. So while traction control also helps maintain directional stability, vehicle acceleration may be slower. Only the tires provide traction when accelerating.
- Vehicle stability systems sense when a vehicle "deviates" from the intended course around a corner (determined by comparing the onboard accelerometer's readings with the vehicle's speed and the driver's inputs). The vehicle stability system selectively brakes any of the four wheels and/or reduces engine power to help correct oversteer or understeer. Only the tires provide traction when cornering.
- No electronic drivers' aid system, regardless of how sophisticated it is, can overcome the laws of physics when the driver exceeds the capabilities of the tires.
- Equally as important, these systems can only operate at peak efficiency when all four tires share matching performance and traction characteristics, as well as are the appropriate size for the vehicle. And unless the vehicle was originally engineered to use different tread designs or types of tires on one axle vs. the other, this means that drivers should make every effort to run the exact same tire brand, tire model and even the same tread depth at each wheel position.
AWD (All-Wheel Drive) and 4WD (Four-Wheel Drive Systems)
All-wheel drive and four-wheel drive cars, SUVs and light trucks have become very popular among drivers who want to maximize their vehicle's traction on slippery roads. And since year-round versatility certainly plays a role, many vehicles equipped with these systems are purchased because their driveline systems make it easier to drive through rain, slush, snow and ice.
The ability of an all-wheel drive system to divide the vehicle's power among all four tires provides a real advantage when accelerating on slippery roads. A 200 horsepower, rear-wheel drive vehicle with a limited slip differential requires enough traction from each tire to accept about 100 horsepower. The best all-wheel drive systems divide that same 200 horsepower among all four tires. Each tire then requires only enough traction to transmit about 50 horsepower. Doubling the driving wheels significantly improves acceleration on slippery surfaces.
However, it is important to remember that while the all-wheel drive vehicle's ability to accelerate in slippery conditions provides a lot of confidence, it doesn't really offer any unique advantage when the vehicle has to stop or turn. This is because the other vehicles also use all four tires to provide braking and cornering traction. Since all-wheel drive vehicles actually weigh more than their two-wheel drive counterparts, bringing them to a stop or turning a corner actually requires more traction.
So, whether your vehicle has anti-lock brakes, traction control, a vehicle stability system or all-wheel drive, it is your tires that provide the real traction. Obviously, the more tire traction these systems have available to master the road and weather conditions the better.