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How Does Electronic Stability Control Work?

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Dear Tom and Ray:

I just purchased a car with ESC, and have read how it is a feature that should be standard on all vehicles -- it could reduce the number of accidents and save more than 10,000 lives a year. If this is so good, why does the car manufacturer provide a switch to turn it off? Under what conditions would I not want to have ESC? Thank you.


-- Dennis

RAY: Great question, Dennis. For those who aren't familiar with automotive acronyms, ESC is the generic term for electronic stability control. We've also seen it called stuff like ASC, DSC, ESP, RSC, SCAS and StabiliTrak.

TOM: ESC works by using sensors to determine where the car is going, and compares that with where you WANT the car to go (by measuring steering and pedal inputs), and then helps direct the car to where you want it to go by applying the brakes on individual wheels. Or, in layman's terms, it helps you maintain control of the car even when you drive like a moron.

RAY: Up to a point.

TOM: Right. There's a point where even stability control can't help you.

RAY: So, when wouldn't you want ESC on? There are two times we know of. One is when you WANT to drive like a moron. People who drive their cars on racetracks sometimes want their cars to slide around and skid. If you're one of those knuckleheads, you might decide to turn off the ESC and take your chances -- presumably, while wearing a crash helmet.

TOM: But the more common reason has to do with getting unstuck when you're stuck in the snow, sand or mud. The way ESC works when you're moving is that if it detects one or more of your wheels slipping, it applies the brake to that wheel to prevent a skid.

RAY: But if you're stuck in the snow, for example, and your drive wheels are spinning, you might not want them to stop spinning -- at least not until the car has broken free of whatever it's stuck in. In that case, you'd turn off the ESC and turn it back on once you're free and on your way.

TOM: But generally speaking, Dennis, it's a life-saving technology, and you want it on all the time. Just like the paper bag we keep over my brother's head when we take him out in public.
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