# MKIV Brake Tech



## spartiati (May 19, 2008)

Hey everyone. Just wanted to post some math I had done to help me make a choice in regards to where I want to go with the brakes on my car. Anyways it's basically a compilation on different combinations of rotors and popular caliper upgrades seen across the mkiv platform. Keep in mind for whoever is reading this that the the F/R bias I calculated was simply looking at one variable at a time, and not the rotors and hydrolic system as a whole. If any errors are found please let me know. 

Thanks 
Stavros

Front calipers piston area difference

Stock: 54mm 2289mm stock 
Boxster: 36/40mm 2271mm -0.7%
R32: 32/42mm 2188mm -4%
17z: 34/36/38mm 3057mm 33.5%
18z: 30/34/38mm 2748mm 20%
996tt: 36/44mm 2537mm 10.8%

Front rotor diameter difference

280mm stock
312mm 11.4%
334mm 19.3%

Rear caliper Volume difference

Rear 38mm 1133mm stock
Boxster 28/30mm 1321mm 16.59% 

Rear rotors upgrade kits

232mm stock ------
254mm 9.5% stock
280mm 20℅ 10.2% 
300mm 29.3% 18.1%
310mm 33.6% 22%

Front Bias based on rotor alone

Stock (F/R)
280/232 54% 
312/254 55% 
334/254 57%

Other potential combinations (F/R)
312mm/280mm 52.7% 
312mm/300mm 51%
312mm/310mm 50.2%
334mm/280mm 54.4%
334mm/300mm 52.7%
334mm/310mm 51.9%

Front bias based on 38mm rear caliper

Stock: 54mm 66.9%
Boxster: 36/40mm 66.6%
R32: 32/42mm 65.9%
17z: 34/36/38mm 72.6%
18z: 30/34/38mm 70.8%
996tt: 36/44mm 69.1%


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## GasInMyVeins (Jul 11, 2010)

Here's a spreadsheet I did for the same purpose. All of my bias calculations include the whole system, but they assume the same pad height. That's obviously not true, but I don't have pads for all of these lying around to measure.

spreadsheet on Dropbox


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## BH17DNB (Feb 21, 2011)

just a thing that popped up to me, how can the stock caliper with 1 54mm piston 2289mm have only 20% surface then 18z: 30/34/38mm 2748mm? you should multiply the 18z surface by 2, since it has a total 6 pots, making it 5497mm. 
You seem to have calculated only one side of a caliper.

Also do you have info on upgrading the M/C on a mk4 for a normal pedal feel after upgrading the brakes?


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## spartiati (May 19, 2008)

BH17DNB said:


> just a thing that popped up to me, how can the stock caliper with 1 54mm piston 2289mm have only 20% surface then 18z: 30/34/38mm 2748mm? you should multiply the 18z surface by 2, since it has a total 6 pots, making it 5497mm.
> You seem to have calculated only one side of a caliper.
> 
> Also do you have info on upgrading the M/C on a mk4 for a normal pedal feel after upgrading the brakes?


No sir. Factory calipers are floating calipers. Even though they have the piston on one side the force acts as if it is compressing on both sides. This I'm 99.99% sure about.


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## clarkma5 (Mar 2, 2002)

There are 280 mm _and_ 288 mm front brake rotors on these cars, and the difference is way more significant than just 8 mm of diameter. 280mm x 22mm rotors are paired with the FS III calipers on TDI and 2.0 cars and 288mm x 25mm rotors are paired with FN3 calipers on 1.8T and VR6 cars. For people who want to do 12.3" or 13.1" rotor upgrades on stock calipers, the upgrade kits out there that just move the stock caliper out on a bracket require the FN3 calipers and its associated knuckle (basically the FSIII's knuckle casting has an integral caliper carrier bracket and the FN3 caliper carrier bracket is its own part, so all you need to do to accommodate different rotor sizes with the FN3 is swap the caliper carrier bracket out to different designs that move the caliper to the correct radius. There is also the Audi TT/R32 knuckle, which accepts the FN3 caliper and carrier bracket AFAIK but results in a different suspension geometry, on top of being forged aluminum and lighter weight?). Here's the Bentley service diagrams.

FS III/280x22mm rotor system on TDI and 2.0 cars









FN3/288x25mm rotor system on 1.8T and VR6 cars









For anyone in a 2.0 or TDI who wants to do the "cheap TT rotor upgrade", it involves procuring the correct knuckles (aka wheel bearing housing assemblies) and calipers to do the rotor upgrade, so it's not so easy.


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## BH17DNB (Feb 21, 2011)

spartiati said:


> No sir. Factory calipers are floating calipers. Even though they have the piston on one side the force acts as if it is compressing on both sides. This I'm 99.99% sure about.


Thank you! i did not know that! I'll look into it though.


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## spartiati (May 19, 2008)

My apologies. I completely screwed that up. I wasn't going to included the TDI/2.0 setup originally because it involves swapping out spindles etc... With that said I mixed up from rotor sizes and though they were 280mm. I'll redo the math where appropriate.

Also can anyone confirm the piston sizes for the r32 front calipers and the Porsche 996t big red. Couldn't confirm the r32 caliper size but knew I had seen those numbers somewhere. Also for the 996t I know the larger piston is 44mm, but I've seen some reports of 36vs38mm for the smaller piston.


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