| |
>Great theory, but unfortunately it defies the law of physics.
Don't EVEN talk to me about physics. What's your engineering/physics
background Phil? Why don't you ask the list how many people
here have engineering degrees?
Nothing we've said defies any laws of physics.
If you've got proof otherwise, then present it.
>You are also missing the point here.
No, you made a point that is not relevant to the discussion.
Yes we know the front brakes always do most of the braking. IRRELEVANT.
The point is that that the way rear brake proportioning is simulated
on the 96+ cars may cause premature wear. Read what I'm saying
before you blow it off. Please don't reply until you can refute what
I'm proving on technical grounds.
>The ABS isn't brake biasing anything!!!
Then the problem is with the term bias. Replace with "proportioning".
The ABS is simulating a brake proportioning valve.
The only way that can work is if you send the full braking force
to the rear, and the ABS cleans up after the mess that creates
in terms of lockup.
That *IS* in fact how it works.
>The ABS system does control the locking up of a particular wheel when it
>senses different wheel speeds.
And in this case the lack of a variable mechanical rear brake
proporting valve means the ABS channels for the rear have to
prevent lockup. Call it "anti-bias".
>The proportioning valve used in the older cars was, as you point out,
>for fully laden cars. But had no effect with one or two people on board.
But here's where you're missing the point. Let's talk in terms
of what that valve did. When the car is unloaded (no rear passengers)
the valve only allowed a certain amount of rear brake pressure.
Let's call that number 10 units of pressure. When the car is
loaded, you want to allow more pressure to the rear brakes (nothing
changes at the front, but the *ratio* between front and rear changes
as a result of more pressure going to the rear). Let's call that
20 units of pressure. Let's say the front always gets 30 units of
pressure.
So unloaded.. front/rear ratio = 30/10
Loaded. front/rear ratio = 30/20 (valve
The proportioning valve controls this. Presumably when it's fully
open it allows the most pressure so we assume that the master cylinder
supplies 20 to the rear and the valve passes all of it when the
car is loaded.
Now we move to the 96+ cars and remove the proporting valve.
We will have to account for the fact that the car may still be loaded
so at some point we still have to supply 20 units of pressure to
the rear brakes.
But wait, there's no proportioning valve. This means we have to
supply 20 units of pressure to the rear from the master cylinder
ALL THE TIME. (any time we're under maximum braking)
Phil, stop here.. read what I said again. We have to supply the maximum
"under load" pressure to the rear brakes EVERY TIME we slam on
the brakes. We can't supply 10 units of pressure and hope it's enough
if the car is loaded. We supply 20 units knowing it is enough for
the fully loaded condition.
But what happens if we supply 20 units of pressure to the rear
when the car is unloaded? Why of course.. it locks the rear tires.
If the rear locks before the front (even when the front is doing
more work) this is REAR BIAS. It doesn't mean the rear does
more work. It means the rear locks first.
What prevents them from actually locking and bringing the rear
end around? The rear ABS channel.
The job of a rear brake proportioning valve is ultimately to
prevent the rear tires from locking up before the fronts, while
still allowing maximum braking under all load conditions..
Now the ABS does EXACTLY THE SAME THING. Prevents the lockup of
the rear tires while still allowing maximum braking under all loading.
They are doing the same job, which is why we say that the
ABS is controlling rear brake bias, or rear brake proportioning.
I can't figure out why you're trying to convince us otherwise.
>For the folks who removed/disabled the ABS system, they should have
>installed a driver controlled brake biasing valve in their car for track
>events.
Once again proving the very point we were making.
>Again the front brakes do the work on these cars not the rears.
They do MOST of the work, under almost all conditions, but
the brakes still have to be able to send more (more than it usually does,
not more than the fronts) braking to the rear when the rear of
the car is loaded. In FACT, it does this every time you slam
on the brakes, and the ABS prevents the tire lockup that WILL
occur otherwise.
>The only way for them to wear before the front pads is for the reasons
>I've previously stated.
Talk about missing the point.
The point is that because the 96+ cars send maximum braking to
the rear (still less than the front.. but that's irrelevant)
it causes undo pad wear. It's harder on the pads to be ABS
cycled than applied continuously.
>It's not the ABS system, contrary to any anecdotal posts to the list.
The disrespect you show for the members of this list when it
comes to technical topics never ceases to amaze me. What
exactly is your training Phil? How much Auto-X have you done?
Road racing? How many times have you pulled your engine apart?
When's the last time you built a VW for racing purposes, or
even driven one well beyond its limits of adhesion? How often
do you drive your car on 3 wheels? Ever experienced the "ABS sledride"?
Blowing off repeatable "anecdotal" evidence of serious problems seems
to be a classic VWoA condition. Glad to see you've got
the company attitude so well Phil.
Noone here drives around doing handbrake turns in the dry every day.
(and you'd have to do it EVERY DAY)
The handbrake only locks when it freezes, and I'll bet money that
most of the list doesn't even see ice and snow.
The fact is that for MANY people the rear brake pads wear up
to twice as fast as the front pads under normal driving conditions.
ian
[...] 13 lines deleted
|
>
>
>
Thu Dec 10 12:38 CST 1998