Can ABS increase the braking distance of a car? Question: Can an ABS (Anti-lock Braking System) instead of decreasing the braking distance actually increase it? If yes, is this its general behaviour, or only in specific circumstances?
Wikipedia claims that on some surfaces (including loose gravel and snow) "ABS may significantly increase braking distance" without, however, explaining this alleged behaviour. The article provides references for this claim, but I could no find any substantiating information in them. Therefore I would like to submit to the community the questions

*

*whether ABS can actually increase the braking distance

*and how is it physically possible, that on some surfaces the distance increases while on other it decreases ?

If possible, please back up your answer with citable references.
 A: The main reason why ABS shortens the braking distance, is because the static friction between the tyres and the road surface is larger than the sliding friction. By making sure the tyres are rolling, the tyres will have the larger static friction with the road surface than if they are sliding, resulting in a larger maximum deceleration of the car.
A reason why ABS could lengthen the braking distance is because it is not perfect. It tries to achieve as much friction as possible, but needs to avoid the wheels locking up. That requires a iterative process: apply as much braking as possible, but back off when the wheels start to lock. As a result of that process, it will apply a little bit less than optimum braking force. If the static and sliding friction of the specific surface are almost identical (for example, on ice), then the resulting sub-optimal braking force may be less that the sliding friction.
A: It sure can and it does often. The purpose of ABS isn't to shorten the brake distance compared to a professional driver but to provide some level of steering control while braking.
If the wheels lock up, then they no longer have a preferred direction of skidding and the driver has zero control over what the car does.
But by pulsing the brakes and letting them rotate then the tires can produce side loads that allow the driver some level of control.
You can read more about this on Tire Rack's tire tech webpage

Anti-Lock Braking Systems (ABS)
By automatically intervening to prevent tires from locking up and to avoid uncontrolled skidding, an anti-lock braking system (ABS) allows tires to maintain rolling contact with the road surface when braking. ABS protects tires from flat-spotting by rapidly and repeatedly pumping the brakes faster than humanly possible. In addition to reducing tire damage, ABS offers improved vehicle control and generally decreases stopping distances on slippery roads.

The moral of the story, and what they teach in driving schools, is  that during a panic stop DON'T FORGET TO STEER while braking also.
