Quote:
Originally Posted by brentil
As long as you don't hydroplain or slide on some surface you'll usually stop a little shorter without ABS. ....
Not necessarily so in today's ABS. If you notice, the rags almost never get a car without ABS.
Reason: the best measured stopping distances today, are, 9 times out of 10, with properly tuned ABS.
A human driver may be able to match or beat ABS on
some of the attempts at maximum stopping, but not consistently. I know this because I used to think this as well, until it was demonstrated to me.
You've generally got to hit just the right slip for straight line braking (somewhere between 8% to 15%) - and depending on the tire, this can be relatively easy, or devilshly difficult. But to do it 5 times in a row is EXTREMELY difficult. To beat or match ABS 10 stops out of 10? Not unless you test cars for a living and have over 1500 tested stops under your belt - and THEN only maybe.
The other reason that ABS is usually a better stopping distance is stability. To avoid premature rear lockup, the use of a proportioning valve is typical in a non-ABS setup. With ABS, you many times can rely on the system to prevent lockup, either by having an electronic control on proportioning, or by getting aggressive on proportioning and just letting slip control handle lockup. The net result: more brake force at the tire patch, because you don't have the prop valve biasing braking to the front to avoid rear wheel lock. Therefore: shorter stopping distance.
What I typically see happen with non-ABS stops in 10 attempts are: two to four relatively bad stops as the driver gets to know the car and how well it brakes, where lockup occurs, how "modulatable" (is that a word?) the pedal and apply system is... Moderate probability of a tire flat spot.
The next several attempts tend to look like a typical autocross - gradual reduction in stopping distance, with a +10' flyer here and there. The last stops are generally over-agressive and result in the need for a new set of tires, and also tend to be longer than the rest.
Overall range of variation - for many drivers, it's over 25' or 30'. The average stopping distance is no where near the average of an ABS car.
Then the driver heads over to the ABS car, and slams 10 stops that are within 5-8 feet of each other.
Don't get me started on "evasive" braking in a non-ABS vs. ABS car.
Today's four channel systems use more advanced logic - wheel slip detection, yaw estimation, all kinds of neat stuff - and can adjust the amount of braking force on the fly. They operate at higher frequencies... they are just not like the old systems that were on the Cavalier, or Rear-only systems on trucks.
Bottom line: BUY the ABS. It's definitely worth the few hundred.
