ABS and Stability Control.

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ABS and Stability Control.

Automakers would sell a lot more anti-lock braking and electronic stability control systems if they could also install those devices in every vehicle. In the showroom, it's hard to see why a computer that can't access the internet is worth $1,000 or more. However, if when things turn swampy on the highway, drivers could push the Pause button on the time machine and then swipe their Visa card to buy a computer-assisted butt-saving, consumers would probably purchase A LOT more ABS and stability control systems.

High-Tech Faith.

ABS and electronic stability control have the potential to save thousands of lives and prevent countless accidents every year. However, it's difficult to appreciate their promise. We'll aspire to explain how these systems work and how a driver can maximize their potential.

Personally, I would no more purchase a car without ABS than one without seatbelts. Along with stability control, it's tops on the list of features-far above subwoofers bigger than an extra-large pizza-I want on a car my teenage daughter will be driving.

Imagine being able to have Tony Stewart or Michael Schumacher instantly take the wheel when you encounter a red-light runner, a blown tire, or a herd of deer. ABS allows you to both stop shorter and maintain steering control during emergency braking. Stability control minimizes your chances of spinning out or sliding nose-first off the road.

ABS Facts.

Tires have much less grip when they're sliding than when rolling. Race car drivers are trained to balance the tires on the verge of lockup: right on the grip peak. Under emergency braking, ABS does just about the same thing: It releases brake pressure just before the tire starts to slide and reapplies pressure when grip returns. It does this many times per second to keep the tire at its peak grip. All you have to do is hold the brake pedal to the floor.

Without ABS, if you attempt to steer during emergency braking, at least one tire is almost certain to lock up. If it's a front tire, the car won't turn and will slide into whatever you're trying to avoid. If a rear tire locks up, the car may spin out.

Stability Control Facts.

Stability control uses the same idea in reverse. Stability control applies the brakes on the end of the car with too much grip. Let's say a driver encounters a patch of ice while accelerating onto a right-turning interstate on-ramp. The rear tires lose grip and the car begins to spin out. Engineers call this "oversteer," and stock car drivers call it "loose." The front tires have too much grip in relation to the rears. The stability control computer applies the left front brake or maybe both front brakes. This reduces the traction of the front tires to bring them in line with the rears.

Most stability control systems also will offset loss of front grip. Change the scenario to a right turn on a two-lane road with water-filled "wagon-wheel ruts." With this car, the front tires lose grip first and the car slides nose-first toward on-coming traffic. To the driver, it feels as if the steering column had snapped or perhaps the left front tire has blown. Engineers term this "understeer," while stock car drivers call it "push." This time the rear tires have too much grip in relation to the fronts. So the computer applies the right rear brake. If the driver is pushing the brake, some systems will release brake pressure on the over-taxed left-front tire. This reduces the traction of the rear tires and helps the car turn.

All stability control systems also include traction control (but far from all traction control systems include stability control). If the car is fishtailing or losing front grip because the driver is too hard on the accelerator, traction control cuts engine power (sometimes by interrupting electricity to the spark plugs) or applies the brakes to the driven wheels, or both.


Some bits of warning: Some early forms of stability control acted only to quell oversteer and did nothing to cure understeer. This could create a rude surprise if the driver didn't notice that the roads were slippery. Also, there are some conditions-especially during winter and off-road conditions-that early generation ABS doesn't produce as short of stops as with wheels locked. However, even then you don't risk spinning out and also retain some steering control.

As a driver, how do you fully exploit these systems? For ABS, it's easy. In an emergency situation, POUND THE BRAKE PEDAL as if you're trying to break it off, HOLD IT TO THE FLOOR, and-this is important-STEER AROUND THE SITUATION. For stability control, there's little you need do except to explore its potential in a safe environment: Find an empty parking lot (with no obstacles) on a rainy or snowy day and wrench the steering wheel in a stupidly aggressive manner.

Experienced performance drivers may find that some stability controls don't respond well with their natural instincts. For instance, race drivers are trained to cope with understeer by leaving the steering wheel where it is, lifting off the gas and waiting for the traction to return (and praying the concrete wall doesn't get there first). If you do this with the system in the current BMW 3 Series, for example, it does not recognize you're in a push. That's because most drivers will incorrectly turn the steering wheel more into the corner. If you don't make this common error, the BMW system doesn't fully appreciate the level of understeer.

It's important to understand that neither ABS nor stability control CREATE grip. Nor do they offer diplomatic immunity from the laws of physics. There's a speed at which every car will go out of control, regardless of how sticky its tires, sophisticated its suspension, and advanced its computer-based driving aids. If it's rainy or icy, that limit speed may be quite low. Even if it's dry, if you enter a curve marked 25 mph at 80 mph, you may be headed for the hospital.

What's in a Name?

What's the difference between ESP and VSC? DSC and VSA? StabiliTrak and AdvanceTrac? All describe that company's version of electronic stability control. (Strangely, none call it ESC.)

It's similar to the distinction between "full-time four-wheel-drive" and "all-wheel-drive"-the identical function is called different things by various companies. Sure, there are small differences in how each accomplishes its goal, but you need an engineering degree, or at least a pocket protector, to figure out the nuances.

Here is what some companies call their electronic stability control:

Honda, Acura
VSA (Vehicle Stability Assist)

Audi, Chrysler, Mercedes-Benz
ESP (Electronic Stability Program)

BMW, Mazda
DSC (Dynamic Stability Control)

General Motors

Active Handling

Jaguar, Land Rover, Nissan
VDC (Vehicle Dynamic Control)

Lexus, Toyota
VSC (Vehicle Skid Control)

Ford, Lincoln

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