996 Rear Caliper Retrofit - Brake Bias

[BTB]

Hi all,

I’m considering doing the 996/986 S rear brake caliper retrofit on my M3. I have the genuine Brembo GT 355mm 4 piston kit on the front which are fantastic, but my stock rears could use a rebuild and obviously the Porsche 996 calipers would look great. However I’ve seen mixed figures online:

Does anyone know the effect the 996 rear caliper piston geometry has on brake bias on a standard M3? I’ve seen that it shifts bias rearward, and also forward per different sources. Just wondering y’alls thoughts as I’m not willing to compromise looks for performance, though I know brake bias is to a small extent subjective and down to weight distribution of car, driver preference etc. Car is street driven in warm/cold temps and also tracked.

Thanks in advance!

Brendan

[SWRT_M3]

this might answer your question

[eacmen]

Hi all,

I’m considering doing the 996/986 S rear brake caliper retrofit on my M3. I have the genuine Brembo GT 355mm 4 piston kit on the front which are fantastic, but my stock rears could use a rebuild and obviously the Porsche 996 calipers would look great. However I’ve seen mixed figures online:

Does anyone know the effect the 996 rear caliper piston geometry has on brake bias on a standard M3? I’ve seen that it shifts bias rearward, and also forward per different sources. Just wondering y’alls thoughts as I’m not willing to compromise looks for performance, though I know brake bias is to a small extent subjective and down to weight distribution of car, driver preference etc. Car is street driven in warm/cold temps and also tracked.

Thanks in advance!

Brendan

from the m track mode thread:

looks like the zcp bias is nearly the same as the 996 conversion according to this table:

https://thebuildjournal.com/tech-guides/brake-bias-chart-e46-m3/

stock 1:54.1 – 60.6%F 39.4%R
zcp 1:38.1 – 58 %F 42 %R
996 1:39.1 – 58.1%F 41.9%R


Sent from my iPhone using Tapatalk

[BTB]

Oh dang, didn’t see that chart on build journal! It looks like using OE fronts with 996 rears results in 61.4% F / 38.6% R which is outside the stock range of 60.6% F / 39.4% R (standard) to 58% F / 42% R (ZCP).

Presumably my Brembo GT4 kit is interchangeable with oe fronts wo changing bias? I’ll have to look into this and play with that brake bias calc as well, thanks guys!

[BTB]

Ahh I see, my Brembo bbk is the F40 caliper w 355 discs. With oe rears that means my bias is 62% F, switching to 996 rears only makes it worse at 62.7% F. Probably not the best route then

[maupineda]

out of curiosity, what are the piston sizes of your Brembo callipers.

[BTB]

out of curiosity, what are the piston sizes of your Brembo callipers.

Trying to figure that out right now hah! Build journal has supposed brake bias but nothing on piston sizes. This table shows piston sizes for racing calipers but not GT. Nothing in this on piston size

[BTB]

out of curiosity, what are the piston sizes of your Brembo callipers.

Got it! See P/N guide: https://www.lpiracing.com/Brembo-Cal...uide-c9150.htm

I have the 1B3.8015A3 kit (type III rotors and silver calipers) which means it's the GT1 4-piston (F50 type). 40mm and 44mm pistons

[S14]

Ahh I see, my Brembo bbk is the F40 caliper w 355 discs. With oe rears that means my bias is 62% F, switching to 996 rears only makes it worse at 62.7% F. Probably not the best route then

I think if you are trying to nail down the bias, you need to figure out your piston area on each axle and do some maths.

[BTB]

FYI, if anyone is curious or ever has a similar question:

The complete two-piece Brembo GT 4-pot kit (1B2.8015A front and 2C2.8001A rear is p/n for kit w slotted rotor) which is supposedly the GT1 'F50 type' caliper has 40 and 44mm pistons on the fronts and 28 and 30mm pistons on the rears. The piston area is therefore identical to the stock 996 rears. Only difference is the rear Brembo bbk for our cars comes with a 345mm disc vs our stock 328mm rotors.

Anywho, I might try for the 996 retrofit afterall. Total piston area is slightly decreased over stock M3 rears, but it is identical to the Brembo kit for our cars. Now to look into 345mm disc conversion...

[maupineda]

Just that the front 996 Porsche calipers are 36/40. So yours are a bit bigger pistons and discs

[BTB]

Just that the front 996 Porsche calipers are 36/40. So yours are a bit bigger pistons and discs

Interesting... 911 needs more rear bias I suspect, so makes sense.

This is what I'm getting with the brake bias calc:

Stock - 66.87% F
GT1 355mm front/OE 328mm rear - 68.77% (current setup)
GT1 355mm front/996 328mm rear - 69.76%
GT1 355mm front/GT1 345mm rear - 68.47%

Granted I'm not positive about pad width so I used 54mm for all. The 996 rear brakes would be identical to GT1 4 piston kit for our cars in terms of bias except that the rotor is 345mm in the kit vs 328mm as stock on ours. Wonder if there's an easy solution to up the rear disc size

Interesting though that the full Brembo 4 pot kit for our cars is supposedly more front biased than stock, and especially more than ZCP setup