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ABS is better?

  1. Sep 13, 2013 #1
    An ABS(Antilock-Breaking-system) prevents the locking of the the wheels in a car when brakes are applied.How is it able to reduce the breaking distance?.As it prevents locking the wheel keeps rolling when brakes are applied which means they still experiences rolling friction whereas when they're locked they experience sliding friction which is greater than rolling friction.So this implies that the ABS should increase the breaking distance right but this is not happening.Can somebody explain why?
  2. jcsd
  3. Sep 13, 2013 #2
    ABS is not designed to reduce stopping distances, it's designed to allow the driver to maintain control of the car.

    ABS does generally tend to increase stopping distances over what a professional racing driver could manage without it. For the average lemming driver though, it is a huge benefit. You cannot stop faster with the wheels locked up than you can with them still turning as it is the turning which generates heat in the brakes, which is a pretty essential part of braking.
  4. Sep 13, 2013 #3


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    This seems contradictory.

    As to who are the lemmings, is debatable......

    https://www.youtube.com/watch?v=QdCDkfEKkUI ​

    When I purchased my latest vehicle, I was not aware that it had an ABS. It wasn't until a police car pulled out in front of me at an intersection a year later that I found out. (No lights, no siren....)

    In the 4 years I've owned the vehicle, the ABS has activated on only two other occasions.

    I would say that the ABS was designed for unexpected emergencies, when panic has you standing on the brake pedal, which as we all know, is the wrong thing to do.

    I believe your "rolling friction" phrase should be replaced with "static friction", as "rolling friction"* is irrelevant to this problem.

    Static friction, as far as I have experienced, is always higher that kinetic friction.
    Therefore, it's best not to lock your brakes.

    * per wiki; "...the name "rolling friction" is to an extent a misnomer."
    I tend to agree.
  5. Sep 13, 2013 #4
    Wouldn't the heat produced due to locked wheels skidding decrease the friction between the rubber of wheels and the road?
  6. Sep 13, 2013 #5

    As seen from the video ABS does help reduce the breaking distance.
  7. Sep 13, 2013 #6
    Kozy has it spot on.
    Its designed to prevent lock ups under panic braking. For the dual bonus of

    a: not being locked up. A rotating wheel has more braking capacity than a sliding wheel.

    b: allowing you to steer. This was the original reason for the systems introduction.

    The reason for this is that a rotating wheel bases its grip as a function of static friction when rotating, when its sliding its retarding force is based on kinematic friction.

    ABS always cuts in before the grip limit based on slip, some systems are more aggressive than others. Old systems used to cut in fairly early to be reliable, so much so that controlled used of the brakes would stop you in a shorter distance.

    Threshold braking is a technique that stops the cars in the fastest time. It requires quite a lot of skill and feel to pull off. It will stop you faster than abs braking.

    Modern abs systems are better than the used to be, but its still extremely frustrating when abs cuts in when you know you have grip to spare.
    Last edited: Sep 13, 2013
  8. Sep 13, 2013 #7
    Yes I agree, it does a bit.

    ABS will stop you quicker than you would if you locked up the wheels, for the reasons mentioned. However, ABS cannot stop you quicker than threshold braking, but as Chris said, that's quite difficult for most people, especially under panic braking.
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