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Originally Posted by stingc
This is not true at all. Locking up the wheels lengthens the stopping distance considerably (~20-50%). It also destroys your tires at high speed. Disregarding directional control issues, there is an optimal brake pressure in all conditions, and almost nobody has the skill to apply it in an emergency, or on wet and icy roads (where you have no tire squeeling to help you out).
ABS automatically figures everything out for you. It does bias things so that you retain some directional control at the expense of stopping distance, but it does both better than almost any driver when they're not expecting something (although you'd probably have quite a bit of trouble getting them to admit this even to themselves...).
There are a number of other issues as well which a good 4-wheel ABS system will take care of that no driver could. In the real world, it's often true that available traction will be considerably different on each tire. ABS can individually control each of those calipers. The driver only has one brake pedal, so there's no way that he could do this.
Even on a perfectly uniform surface, you still have to worry about the different brake pressures on the front and rear axles. The optimal split depends quite a bit on the amount of traction availalbe, among other things. For the best braking, it therefore should not be set once and for all from the factory. Cars without ABS had to make do with a front-rear brake bias designed so that the rear wheels would never lock up before the fronts (for safety). (Good) ABS systems effectively remove this compromise.
While there are bad systems out there, the good ones are very useful. And for those saying that it's too expensive because it's rarely useful, realize that it more than pays for itself even if you only need it once.
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I'll qualify it, sorry. I should've earlier, but I was distracted. In the optimal conditions and at the limits of vehicle performance, ABS will improve braking times. These are the figures most often cited, because they're the ones that show ABS in the most beneficial light; on dry pavement an ABS vehicle may stop as much as 20 ft earlier than one with locked tires. In any other situation (snow, ice, gravel) a locked wheel will stop shorter. It's true that this causes a great deal of damage to the tires, but I would propose that the well-being of the tires is secondary to the well-being of the vehicle and the passengers inside. The downside to the locked wheels is a loss of directional control. You will slide in a straight line (as long as the wheels stay locked) and the car may even rotate on it's axis, which gives a sense of veering even though you continue to move straight.
ABS essentially serves as a substitute for driver ability - the computer will determine how to brake so that you don't have to. As I said, for people without the time or inclination to learn proper braking techniques this is beneficial. For the few who actually do learn how to brake properly it can be a hindrance.
I will concede that a computer is in some cases more efficient than a person. This is especially true in a brake and avoid situation; even a well-trained driver cannot find the braking threshold as quickly and efficiently as a computer. If I need to maintain control of my car while braking, it's easier to just mash the pedal and let the computer take care of the details than it is to feather and look for that point of lock-up myself; the computer can also get consistently closer to it than I can without actually locking the wheels.
I'm not opposed to ABS in most situations; the driving practices some people learn leave me absolutely appalled. I learned a lot of what I know from a professional driver who races in local circuits. He in turn learned his skills from the schools that are mandatory for someone who wants to race stock. I recognize that very few people have the benefit of a teacher that skilled or experienced and for them, tools to assist them in the day to day operation of the vehicle are beneficial bordering on essential. For those who do have the training, they're not necessary.