quote:
Originally posted by moribundman:
The ABS system will pulsate around that point. A experienced driver can "find" the close to skidding point and do a better job than the ABS system.
I am going to have to disagree here. There are ABS systems that can simply stop the car faster than even the most experienced driver can (by modulating the brakes). And, then again, there are cars with ABS systems where this is not true.
ABS systems that cycle by decreasing brake pressure slowly until traction is found and then increasing pressure slowly until traction is lost, can operate the tire much closer to the edge of traction than any driver can reaslistically hope to achieve, even under ideal circumstances. There may be 25 drivers in the whole world that can achieve better stopping distances than these systems in ideal test setups. Throw in debris on the road, water, leaves, children in the back seet and there is no hope for a driver to achieve as good a stopping distance as these cars. Ferraris, Porsches, some Mercedes, and some BMWs get these systems. Other higher end cars may also get these systems.
Unfortuantely most ABS systems decrease the braking pressure too fast and then increase the braking pressure too fast. Operating like dozens of tiny skids per second rather than cycling around the point of best traction. Even here, though, ABS will beat 95% of all drivers 95% of the time. Many suspensions are not sufficiently stiff (and damped) to enable ABS systems to find the point of best traction.
And then there is the problem of upgrades to the suspension, brakes, tires and wheels. An ABS system has its time constants and valving sized for the tractio of the default tire combination and the rotational inertia of the original tire/wheel/brake rotor combinationi. Changing any of these variables can move the ABS system far away from its optimal performance. No manufacture, that I know of, will give the average back yard mechanic the information required to move the ABS system back towards optimal. (Think Lawyers)
Finally, as tires age they loose traction. You may feel that getting 80,000 miles from a set of tires is saving you money. You might be surprised to find that best case braking performance at 79,000 miles is 30 or more feet longer than identical tires when new.