A competent authority has assessed that ABS brakes INCREASE stopping =

distances on gravel (metal) surfaces by typically 20+ percent.

        http://en.wikipedia.org/wiki/Anti-lock_braking_system
A 2003 Australian study[2] by Monash University Accident Research Centre =

found that ABS:

  a.. Reduced the risk of multiple vehicle crashes by 18 percent.
  b.. Reduced the risk of run-off-road crashes by 35 percent.
On high-traction surfaces such as bitumen, or concrete many (though not all=
) =

ABS-equipped cars are able to attain braking distances better (i.e. shorter=
) =

than those that would be easily possible without the benefit of ABS. Even a=
n =

alert, skilled driver without ABS would find it difficult, even through the =

use of techniques like threshold braking, to match or improve on the =

performance of a typical driver with an ABS-equipped vehicle, in realworld =

conditions. ABS reduces chances of crashing, and/or the severity of impact. =

The recommended technique for non-expert drivers in an ABS-equipped car, in =

a typical full-braking emergency, is to press the brake pedal as firmly as =

possible and, where appropriate, to steer around obstructions. In such =

situations, ABS will significantly reduce the chances of a skid and =

subsequent loss of control.

In gravel and deep snow, ABS tends to increase braking distances.

On these surfaces, locked wheels dig in and stop the vehicle more quickly.

ABS prevents this from occurring.

Some ABS calibrations reduce this problem by slowing the cycling time, thus =

letting the wheels repeatedly briefly lock and unlock. The primary benefit =

of ABS on such surfaces is to increase the ability of the driver to maintai=
n =

control of the car rather than go into a skid =97 though loss of control =

remains more likely on soft surfaces like gravel or slippery surfaces like =

snow or ice. On a very slippery surface such as sheet ice or gravel it is =

possible to lock multiple wheels at once, and this can defeat ABS (which =

relies on detecting individual wheels skidding). Availability of ABS =

relieves most drivers from learning threshold braking.

But part of the answer is that on heavy snow, locked wheels can be useful =

because they gather up a "wedge" of snow which helps to slow the vehicle. =

ABS allows this wedge to clear every time the wheels are unlocked. The same =

can apply on sand in some conditions.

A June 1999 NHTSA study found that ABS increased stopping distances on loos=
e =

gravel by an average of 22 percent [1].



_________



Very interesting paper on ABS brake accident stats.

No great relationship to gravel roads.






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