[200q20v] Re: [audi20v] RE: front brake upgrades - another POV

[Bernie Benz]

Scott lectures as follows:
"Remember, if you put 800psi on 2 pistons vs 4, you have more clamping force
on 4 piston calipers."

Not so, gerneraly speaking Scott.  You're not being specific on your caliper
design detail.  A two piston caliper generally implies two pistons on one
side of a single sided caliper.  Likewise, a four piston caliper generally
implies two pistons on each side of a dual sided caliper.

If you are imbracing this convention, your statement is wrong!  A single
sided caliper of given piston area will produce an identical clamping force
per unit applied pressure as will a dual sided caliper having the same
piston area per side.  If you don't believe this, consider the following
simplification.

What is the difference in contact force if you were to push on a rigid wall
with 10 lbs. force, vs, your pushing against my hand, which is actively also
pushing back with an equal and opposite 10 lbs. force?  None!  The contact
patch doesn't know/see any difference,  Conclusion:  The advantage of dual
sided calipers over single sided calipers is trivial, being only a function
of caliper mounting and centering differences, and possibably weight.

Regards,  Bernie

 
> From: QSHIPQ at aol.com
> Reply-To: Scott Justusson <qshipq at aol.com>
> Date: Sat, 30 Jun 2001 12:35:25 EDT
> To: "Audi 20V" <audi20v at rennlist.org>
> Subject: [audi20v] RE: front brake upgrades - another POV
> 
> Coupla points on this thread:
> If you have a locking rear diff, you don't have a dual diagnal braking
> system.  You can't, you only have one line to the rear.  This system is on
> ALL audis with Gen 1 lockers, Gen II (torsen C/ locker rear) and Gen III
> (Torsen/electronic C/ Torsen rear - v8).
> 
> The front ABS on the Gen II (specific to all 90q series cars) is independent.
>  The rear ABS is a single control which means if either rear wheel senses
> lockup, both are solenoid reduced to the wheel that is locking up the most.
>  In 4 channel systems, the fronts are also independent, and although the
> rears have 2 individual controllers, both rears are reduced the same amount
> with any rear activation.  Thinking this thru, I'm sure this is a liability
> issue, and a much easier ABS algorythum to program.  
> 
> Reading the Audiworld post, I'm not sure the "proof" of dual diagnal braking
> is a valid offer that big brakes don't help up front.  Remember, if you put
> 800psi on 2 pistons vs 4, you have more clamping force on 4 piston calipers.
> You also have more swept area with larger brakes, and more heat dissapation
> with larger rotors.  
> 
> WRT the rears, Tom Vv referenced a post i put up a while ago.  Bottom line is
> this, audi has published data on the 80/90q that shows 80% front weight
> transfer under max braking.  If you take a 3400lb car the fronts need to
> support 2720lbs of braking vs the rears supporting 680lbs.  If you go to
> bigger front brakes (assuming bigger/better tires as well), you have
> increased the g's generated in stopping, which shifts even more weight
> forward, which reduces the need for more braking rear further.
> 
> Interesting, I just got into this thread on the S car list, which I will
> forward to this list as well.  BTW, I got a ride in Tom Saltinos S4 at mid OH
> just yesterday, and found the brakes to be good upgrade.
> 
> HTH
> 
> Scott Justusson
> 
> 
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