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RE: Brembos, big reds, etc. (The truth and long)

I have been quietly monitoring all the discussion regarding brake upgrades
and I feel it is time to provide some facts that seem to be lacking.

First, let me clear the confusion regarding sizes of calipers. There is only
one "Big Red" (hereinafter referred to as "BR") caliper. It originally came
on front of the 91 Porsche C2 Turbo and has been/is used on the 993, 993TT
993 GT1 & GT2 and the 93-95 928 GTS. The pad used with this caliper is 5.18"
x 2.95" with a new depth of 18 mm.

The next size smaller caliper hereinafter referred to as "S4 caliper") was
the front caliper on the 88 944TS, 89 944T, 89-91 944S2 w/M030 package,
92-95 968 w/M030 package, 928 S4 and 928 GT. To the best of my knowledge, it
was never available in red. The pad it uses is 5.18" wide x 2.8" tall with a
new pad depth of 17 mm.

Note I am only addressing the calipers sizes first. The rotor sizes will
follow as they play an important part in the brake force and balance

It should be noted the piston sizes in both of these previously mentioned
calipers are the same. The only difference is the total swept area of the
Big Red caliper. 15.28 sq. inches total swept area for the Big Red vs. 14.5
sq. inches for the smaller caliper is an approximate 5.4% increase in total
swept area.

Also important is the piston combination in the Porsche caliper is
unavailable in any other caliper from Brembo. Literally everything regarding
the Porsche caliper is unique to Porsche and Brembo's contract with Porsche
prohibits them from selling any parts etc. for the Porsche calipers. Steve's
"Ultimate Garage" page states the bolts are larger in the Porsche calipers
however I have been unable to verify this. (And believe me, I have been

The rear calipers on all the cars mentioned above are the same size however
the piston size combination differ. As well as Porsche using different
combinations of piston sizes in the rear calipers they use different brake
pressure regulators and master cylinders to achieve the correct front/rear
brake balance.

The rear calipers were, depending on the vehicle, available in red and use a
pad size of 3.48" x 2.58" with a new pad depth of 18 mm. This pad has a
total swept area of 8.98 inches. Note this caliper with a different piston
combination was used as the stock front caliper on the 86-88 944 turbo, 944
S2, 968 and various 928 models.

Another area of confusion is rotor size. The rotor sizes for the cars
referred to above are:

Front				Diameter
911 GT1 & GT2		380 mm
993TT				330 mm
993, 964, 928 GTS		322 mm
944TS & M030 upgrade	304 mm
944S2 & 968			298 mm

GT1 & GT2			I don't know
993tt				322 mm
964, 928 S4, GT, GTS,
944TS, 944 S2 (all)
968 (all)			299 mm

The BR caliper requires 17 inch wheels, the S4 caliper will fit easily under
16" wheels (depending on offset) and the smallest 4 piston caliper should
fit under 15" wheels (have not tried this yet.)

The biggest advantage to larger diameter rotors is by moving the clamping
point of the caliper further away from the center, one gets an increase in
brake leverage. Another advantage is more mass to deal with greater thermal
loads. The downside to this is larger rotating unsprung mass which
ultimately affects both acceleration and turn-in.

I have experience with all three sizes of calipers using them in different
combinations front/rear and with different rear pressure regulators,
different pads, etc. on a 93 968. The car is a daily driver and has been
tracked heavily at tracks around the country. I also race a 125 shifter
kart. I started researching braking systems recently when after speaking
with a number of so-called experts in brake systems including Brembo, Alcon,
CoolTech, and others, I was unable to get reasonable, thought out answers to
what I felt were basic questions. My conclusion is most of the folks out
there, including Brembo, Alcon, CoolTech, etc. do not design these upgrades
as a total system solution. (I know I will get flames on that!) There is
much more to this than bolting on larger calipers and rotors. I haven't
addressed here the additional issues of master cylinder size and booster
size which not only are critical components in regards to pedal feel and
stopping power but have numerous variable related to each of them also.


> -----Original Message-----
> From: owner-quattro@audifans.com [mailto:owner-quattro@audifans.com]On
> Behalf Of Todd Phenneger
> Sent: Thursday, May 13, 1999 4:29 AM
> To: Rob Andrews
> Cc: Paul E. Rivera; Quattro List
> Subject: Re: Brembos, big reds, etc.
> On Thu, 13 May 1999, Rob Andrews wrote:
> > Wait a sec....I'm confused now...I though the big reds did come from
> > 993...look at vwsportusa.com I thought those were the big reds
> or are there
> > BIGGER out there than those?
> 	Well, I thought there were only two varieties of Porsche Brembos
> out there.  The ones that the 911 Twin Turbo and new 996 have.  And the
> smaller ones which I thought were what came on the 944 Turbo, 968, RS2,
> and maybe the 993.  Or maybe the 993 had the BIG ones.  But the real BIG
> Reds are the 911TT units.  I spose the others could be called "Little
> Reds"  :-)
> 	CAn anyone confirm this.  Or were there three different units with
> the 993 being bigger than the 944t and smaller than the 911tt.
> 	Not sure if I helped or confused us more.  Anyone???
> Thanks
> 		Todd