Dodge Durango Forum II Archive

Mike Orth
orthm@attglobal.net

First things first..  Just slamming on the brakes and locking up the wheels is NOT the fastest way to stop a non-ABS vehicle if you're on the street.  In doing so, the driver has given up all control of the vehicle and is just along for the ride.  A tire can generate more grip on the road if it's rolling than if it's locked.  This is where ABS comes into play.

The job of an ABS system it to make sure the wheels keep turning during heavy braking.  This allows the driver to still be able to steer(in 4w abs systems) and brake at the same time.  In rear axle only (2w abs systems), it's there just to try and keep the back end of the vehicle from passing the front end (spinning)during heavy braking.  ABS does NOT stop a car any faster then the same car without ABS.  The difference is the driver in the non-abs car.  A driver that is good at modulating brakes and sensing wheel lock-up can stop just as quickly, but it takes a lot of practice and time to develope that skill.  Sadly, most drivers don't spend time trying to learn it, and just trust that the ABS system will be there when they need it.  I've seen too many instances of ABS failure at the driving schools I instruct at to have %100 trust in ABS.

Another thing that ABS cannot prevent is spinning.  ABS cars can be made to spin like a top in certain circumstances.  More than one of my students found that out during our sessions on a wet skid pad :-) If you're going too fast for the conditions, ABS will not save you.
       
There are situations where it can cause problems as well.  As others have responded, packed snow, gravel, and ice are the most common surfaces that confuse ABS systems.  The main reason for that is the lack of friction between the tire and the road surface.  In this situation, a wheel locks very quickly.  The ABS system responds by releasing the brake pressure at the locked wheel(s).  However, since there's so little friction between the tire and the road surface, it takes longer for the wheel to start rotating quickly enough for the system to think that it's ok to start applying the brakes again to that wheel.  When it finally does, the wheel locks almost immediatly, and the system releases pressure again.  In short, the ABS computer has turned off your brakes...  This is why it is nearly impossible to stop an ABS equipped car with dry weather (or worn out all season) tires on snow.  Some European cars used to have switches to turn off ABS for these circumstances.

Hope this helps,
Mike