[A4] tires, speaking of tires, anyone have any used 17's lay'n around?

[LL - NY]

My point is that I believe you overstated the case that the 3 channel Bosch
ABS system would "totally lose" braking if one of the rear wheels sensed
slip. It will not. It will limit braking force to the limit of the rear tire
of with the least traction, but it most certainly will not be zero unless
you're on a zero mu surface, in which case you shouldn't be driving
anythingthat uses tires as it's only means of stop, go, turn.

And, in the case of the C3 and C4 chassis cars, it has already been
discussed at nauseum that in high mu situations, the weight transfer to the
front axle under threshold braking situations pretty well negates the rear
axle braking effect on slowing the car, any of us whom have pushed either of
these chassis cars to the limit has experienced it. In these cases, having
limited braking from the rear axle really would have no overall effect on
braking distances, and having the ABS function will help retain control of
the rear axle, though not as well as a properly trained delicate foot would.


And as George has so rightfully pointed out, at least the ABS generation of
my type 44 was pretty over sensitive on loose surface situations. I did
appreciate ABS defeat on theat car. The ABS of the 95.5 //S6 has shown
itself to be significantly less sensitive, and for the most part the ABS of
the Saabaru (okay, diff mfg, but 10 years newer software and processors I'm
sure has made it Germany as well as Japan) is pretty darned effective on all
surfaces. In fact, the only time I do defeat ABS on the Saabaru is when
competing in Solo2, where for some reason the ABS system is unable to keep
up ABS reserve pressure in certain situations resulting in nearly complete
loss of brake boost for up to about half a second (no ABS, no boost, feels
like no brake) in competition. The ABS defeat in that case is simply to pull
the fuse, but I guess that is the ONE thing I do like about the stupid
Hydroboost on the C3/C4. I NEVAH ran out of ABS reserve pressure on either
of those cars  But on course, neither was as fast either.

Finally, on the note of manual threshold braking vs. modern ABS, I'm somehow
questioning the validity of your findings at HPDE's vs. the experience of
the testers at both Road and Track, Car and Driver, Autoweek and even
Consumer's Union, whom have the ability, trained testers, and facilities to
do repeated consistent tests on the performance of the brakes on the cars
they test on a professional basis. To a fault, ALL of those publications
state that they produce the most consistently short stopping distances (read
their annual, "how we test" issues) by applying full ABS. They say that they
can occassionally beat ABS, but not consistently, particularly with
contemporary iron. What you may be finding at HPDE's (as do we when we run
Autocross schools) is that you are finding driver inconsistencies. Many,
many drivers do not react appropriately when the ABS triggers in their cars,
and they attempt to modulate their brakes, just as if they are doing
threshold braking. M-B found this which is what encouraged them to invent
the somewhat scary in my book "brake-assist" software that they use in their
cars. SO, if ABS triggers in those driver's cars, many drivers FAIL to keep
their foot firmly on the pedal until the vehicle stops. No full effort,
longer stopping distances. It may well be a driver re-training issue, as
most drivers that attend HPDE's are the kind that are more likely to
attemptthreshold braking (thus modulating the pedal) than the general
population.
But the point is that the professionals (and we're not talking just consumer
mags, the first three on my list I'd place firmly on the "enthusiast" list)
seem to beg to differ what us more "amateur" testers have found. And, I'd
daresay they have not only the milage and hours and experience to back
themselves up, but also the shear numbers and variety of vehicles to do so.
Emperical vs. objective. I'd go with objective.

LL - NY

LL - NY

On 12/28/07, Brett Dikeman <brett at cloud9.net> wrote:
>
> On Dec 27, 2007, at 7:22 PM, LL - NY wrote:
>
> > Hate to point this out, but the wheel(s) that are triggering ABS are
> > being used to
> > the maximum point of availible braking traction, within the limits
> > of the ABS computer
> > and pump, which is nowhere near lost braking. I'd estimate that even
> > the early Bosch
> > series 1 ABS is capable of using nearly 70% the availible braking
> > traction for the activated
> > wheels. And, in the case of the type 44 and C4 cars, loosing the
> > rears will hardly affect
> > things, they're not doing too much braking anyway (virtually no
> > traction due to weight
> > transfer) in a threshold situation.
>
> ABS is not for shortest stopping distance.  It's for avoiding loss of
> directional control from braking- ie spins or directional loss of
> control from uneven braking side-to-side.  That it also provides a
> function which *approximates* threshold braking on dry pavement, is a
> nice bonus; dry pavement is more suited to the way ABS controls the
> brake.
>
> In slippery conditions, ABS is best left as a safety net, because it
> doesn't have nearly the 'gentle touch' required.  My 200q20v's ABS is
> almost completely useless in the snow for actually stopping the car,
> and my folks' Volvo was the same way.  Both vehicles, regardless of
> tire choice, could stop far shorter when the nut behind the wheel
> applied juuuuust enough brakes.  I'm sure most listers have noticed
> the same, if they've ever messed around in a parking lot or just
> tested how much traction was available on the road (something I
> recommend listers do often in slippery conditions for a sense of
> braking capabilities.  I've been very surprised in both ways by
> conditions- I've been in heavy snow that let me stop on a dime, and
> light snow that was slippery as hell.)
>
> At the track or on the street, it's much the same story.  You can slam
> on the brakes and generate a lot of drama, or you can surely apply
> them and STAND on the brake pedal without engaging ABS.  You've giving
> time for the weight transfer to start, for the suspension to load up,
> etc.
>
> I also spent a few years watching attendees do the "panic stop with
> ABS vs. threshold braking" test at WDS.  Even with a basic amount of
> instruction and a few practice goes, a driver can easily and handily
> beat ABS, and it's clear as day when they're standing on the pedal-
> even with snow tires, the wheels stop/start, the car wobbles,
> and....doesn't do a very good job of stopping.  You can even tell when
> some transitions from threshold braking to "oh #@$!" foot-on-the floor
> (one of the informal and optional "contests"
>
> Brett
>