Bosch/automotive brakequattro (To: Robert Deis et. al.)

[Orin Eman]

>
> You WILL find the newer ABS unit to be much better on snow and ice versus the
> older units.  One of the reasons is that on older units, it could "stop" the
> tire every (bear with me, for explanation purposes) 45 degrees of tire
> rotation.  Newer ABS does a better job in modulation AND can "stop" the tire
> every 10 degrees (again, for explanational purposes).  In effect, the braking
> system has gotten more advanced,  Add in traction control with a reverse
> feedback (showing up on some Mercedes, etc. now) for braking, I expect even
> threshold ABS will be moot for me to teach at winter driving schools.  For a
> large movement of the vehicle to the side (emergency lane change to stop
> maneuvers), you'll still have to release some (or all) braking pressure, but
> for most panic moves and stops, just holding full pedal pressure will suffice
> with the latest generation systems coming out.  Ultimately, experiment on a
> snowy parking lot when nobody is around.

And on the on the '97 and '00 A4s, such an experiment revealed...
no improvement over the old system at all.  Stand on the brakes and
slide and slide and slide with the ABS chattering away.  Brake gently
and stop no problem.

I figure in these situations, with the driver standing on the brake,
the wheel locks _as soon as_ the ABS allows pressure to the caliper.
So, you get some braking effect while the ABS detects the wheel is locked,
but not that much because the wheel _is_ locked.  Then you wait while
the ABS cuts pressure to the caliper, detects the wheel is moving again
and finally allows pressure through again.  My guess is that you get
braking perhaps 50%* of the time and almost all of that with the wheel locked.
Can you beat 50% of locked wheel traction threshold braking?  Seems so.

Orin.

*50% is just a guess.  Could be worse, could be better.  Whatever, being
gentle on the brakes in these conditions seems to work better.