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      09-10-2020, 01:32 PM   #1
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Best retrofit for M3 brakes?

I’m hoping to upgrade my brakes (front/rear)... Wondering what is the consensus on the best retrofit?

I’ve seen some people instal Porsche Brembo calipers onto stock rear rotors... but, where to get the brackets? Which year/model Porsche calipers?

Also, I understand M4 rotors bolt right up to stock e92 M3 hub, but where to get bracket for M4 calipers?

What have people done otherwise??
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      09-10-2020, 03:21 PM   #2
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The idea of retrofitting brakes is bang for buck, related to saving money.

I just can’t justify dropping $3k on brakes right now.
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      09-10-2020, 03:28 PM   #3
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      09-10-2020, 04:09 PM   #4
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The most popular retrofitting option is the F8x OEM, no need for bracket just front spindle, I am looking at this option myself.

You will need to work with the ABS sensors, and the spindles can cost you around $500 or more. Used F/R caliper and rotor set will cost anywhere between $1-2.5K, not hard to get around $1.5Kish if you are willing to wait.
This setup, according to some, will have very similar brake bias compared to OEM. I wouldn't mess with the Porsche ones or any other ones myself since that cars are too different.

However, StopTech currently has about 20% off discount, you can get the ST40 Front only kit for about $2200, which IMO is a better option than F8x especially for performance
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      09-10-2020, 10:53 PM   #5
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Quote:
Originally Posted by W12x View Post
The most popular retrofitting option is the F8x OEM, no need for bracket just front spindle, I am looking at this option myself.

You will need to work with the ABS sensors, and the spindles can cost you around $500 or more. Used F/R caliper and rotor set will cost anywhere between $1-2.5K, not hard to get around $1.5Kish if you are willing to wait.
This setup, according to some, will have very similar brake bias compared to OEM. I wouldn't mess with the Porsche ones or any other ones myself since that cars are too different.

However, StopTech currently has about 20% off discount, you can get the ST40 Front only kit for about $2200, which IMO is a better option than F8x especially for performance

Thank you for that. I was weary about messing with Porsche brakes to begin with, but you make some good points.

Regarding the M4 retrofit, do you know the part number for the spindle? Knuckle?

Is it the entire spindle assembly? or just the part itself?
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      09-11-2020, 06:32 AM   #6
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Quote:
Originally Posted by SilverSlug View Post
Thank you for that. I was weary about messing with Porsche brakes to begin with, but you make some good points.

Regarding the M4 retrofit, do you know the part number for the spindle? Knuckle?

Is it the entire spindle assembly? or just the part itself?
All the info you need:

https://www.m3post.com/forums/showthread.php?t=1713861
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      09-11-2020, 07:56 AM   #7
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A couple of things to consider. Swapping out your brakes, (lines, rotors, pads, calipers) on all four corners is not hard, but it's not nothing either. Retrofitting the F80 kit is a bit more with the spindles. So my only suggestion is that it's a big enough deal that you should make sure to get what you want. You probably aren't going to want to swap out brake kits too often. Are you looking for the aesthetic, the performance, both? Track time, street only? From what I understand, the F80 kit is better, but only just, than OEM. Looks better, certainly, but may not be a substantive performance boost. A BBK has the aesthetic and performance but comes at a cost.
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      09-13-2020, 04:07 PM   #8
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Thank you for chiming in. Yes, mainly performance, of course I don’t mind aesthetics of BBK as well. I live in San Francisco, which has crazy steep hills, so brake fade sux.

Are there any other retrofit options other than F80 M4? The used caliper/rotor kits are selling for ~$1,500-$1,800, so with the price of the knuckles, we’re encroaching on StopTech prices.

Any other OEM Brembo or M Performance kits will work??
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      09-13-2020, 07:29 PM   #9
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If you had decent fluid and non oem pads you wouldn't get brake fade driving city streets. I actually find it had to believe you'd fade oem brakes in town at all, but if you've got 10 year old brake fluid that's probably possible.

I track the stock system at in south Florida in the summer with: endless fluid, Ferodo pads, and brass pin bushings. I've gotten pretty quick too, so I assume I'm pushing the brakes pretty hard. Never faded them.

In terms of looking at retrofit brake kits, If you don't upgrade to a much better rotor design (not some other car's oem system) you're not going to gain an ounce of performance over just putting good fluid and hybrid pads (e.g ds2500) in your existing system.

The issue with the oem brake system is not the massive single piston caliper. It's the poor airflow of stock rotors (compared to a nice bbk).

You don't want to invest in bbk, so look at some PFC dd v3's for the front axle. The stock rear's are fine for even very spirited street driving.
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      09-13-2020, 08:43 PM   #10
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Quote:
Originally Posted by SilverSlug View Post
Thank you for chiming in. Yes, mainly performance, of course I don’t mind aesthetics of BBK as well. I live in San Francisco, which has crazy steep hills, so brake fade sux.

Are there any other retrofit options other than F80 M4? The used caliper/rotor kits are selling for ~$1,500-$1,800, so with the price of the knuckles, we’re encroaching on StopTech prices.

Any other OEM Brembo or M Performance kits will work??
I did the math when I was looking at that option, it will most likely cost somewhere around $2100-2300 if you go the F8x retrofit option. The F8x retro is probably the cheapest and most compatible kit you can find.

Sometimes you see the F8x OEM kit for $1000-1200 range but you have to be very lucky or patient. I have seen the calipers only for $600 and that's the lowest I have seen in the US.

No respectable BBK or retrofit options are available for considerably cheaper as far as I know.

IMO ST40 Front+OEM Rear>any retrofit around same price range.
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      09-13-2020, 08:47 PM   #11
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Quote:
Originally Posted by W12x View Post
Quote:
Originally Posted by SilverSlug View Post
Thank you for chiming in. Yes, mainly performance, of course I don’t mind aesthetics of BBK as well. I live in San Francisco, which has crazy steep hills, so brake fade sux.

Are there any other retrofit options other than F80 M4? The used caliper/rotor kits are selling for ~$1,500-$1,800, so with the price of the knuckles, we’re encroaching on StopTech prices.

Any other OEM Brembo or M Performance kits will work??
I did the math when I was looking at that option, it will most likely cost somewhere around $2100-2300 if you go the F8x retrofit option. The F8x retro is probably the cheapest and most compatible kit you can find.

Sometimes you see the F8x OEM kit for $1000-1200 range but you have to be very lucky or patient. I have seen the calipers only for $600 and that's the lowest I have seen in the US.

No respectable BBK or retrofit options are available for considerably cheaper as far as I know.

IMO ST40 Front+OEM Rear>any retrofit around same price range.
How do you suppose the F8X brake retrofit compares to the StopTech ST40 kit in terms of performance?

Are the StopTech brakes a lot better? Or similar?
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      09-13-2020, 09:04 PM   #12
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Quote:
Originally Posted by SilverSlug View Post
How do you suppose the F8X brake retrofit compares to the StopTech ST40 kit in terms of performance?

Are the StopTech brakes a lot better? Or similar?
I don't have any personal experience with the two, but IIRC, the F8x is a little better than E9x OEM, but not a night and day difference, and real quality BBKs will have better thermal capacity for sure.

Some folks with M2C and the 2NH brake (which uses same calipers as the F8x CCB, but steel rotors, a step up from F8x OEM) choose to upgrade to StopTech or similar real BBKs, not sure if it's ST40 or ST60 tho.

Considering the front brakes have much more impact on performance than the rears, and real problem with E9x OEM brakes is not the stopping power but thermal like butte2butte said.

I remember years ago some magazine/website did a test, E9x M3 got slightly better or very similar stopping performance as C63 AMG with OEM BBKs, but E9x have major fading issues.

One other benefit is if you want to sell your StopTech kit or other BBK kit down the road it will probably be easier than OEM/retro
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      09-22-2020, 06:46 PM   #13
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Quote:
Originally Posted by SilverSlug View Post
Thank you for chiming in. Yes, mainly performance, of course I don’t mind aesthetics of BBK as well. I live in San Francisco, which has crazy steep hills, so brake fade sux.

Are there any other retrofit options other than F80 M4? The used caliper/rotor kits are selling for ~$1,500-$1,800, so with the price of the knuckles, we’re encroaching on StopTech prices.

Any other OEM Brembo or M Performance kits will work??
I live in San Francisco.

Unless you're doing top speed runs and braking from triple digits repeatedly, you should not be fading stock brakes on city streets no matter how steep it is.

If anything all you need is some more aggressive brake pads and you will have more than enough braking power for anything you throw at the car.
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      09-27-2020, 03:00 AM   #14
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I have been doing lots of research into doing a properly matched BBK retrofit, with calipers that have as close to stock piston area and front/rear bias as possible.

My first consideration was the F8X setup as it would seem a no brainer, however despite the relatively simple fitment, I've realised that the M4 has a 10% smaller total piston area than the E92 M3, which means a 10% firmer pedal with 10% less modulation, and 10% less torque at the piston.

Here are the caliper stats side by side:

E92 M3 calipers
Stock M3 piston area front 60mm - 2826 x 2
Stock M3 piston area rear 46mm - 1661 x 2
Stock M3 total area 4487
Stock front bias 63%

M4 calipers
F8X M3/M4 front BB-43 (40/40x30mm) - 2512 x 2
F8X M3/M4 rear BB-22 (44x24mm) - 1520 x 2
Total 4032 - 10% firmer - Stock bias 62%

Ideally you want to find calipers that maintain the total piston area to match the capacity of the master cylinder. If you compare the E92 specs with even the Stoptech, we can see that even they deliberately only differ total piston area by 1% and shift the bias slightly rearward:

Stoptech BBK
Stoptech non Trophy st60 front = 36/36/30 - 2741 x2
Stoptech Trophy ST60 32/34/36mm = 2729 x 2
Stoptech st40 355 back = 34mm 32mm - 1711 x 2
Total 4452 or 4440 x2 / 1% harder 61.5 front bias

Brembo GT BBK
Front 6 pot = 30/34/38mm - 2748mm x2
Rear 4 pot = 32/32mm - 1608mm x 2
Total 4356mm x 2 - 63% front bias

To keep as close to stock piston area, ideally you need to find a combination of front and rear that are RADIUS mount to allow for easy bracket fabrication, NOT lug mount. Ideally with the following piston configurations, :

Front 6 Pot
32/34/38mm - 2845 x 2
30/34/38mm - 2748 x 2
30/36/36mm - 2741 x 2
32/34/36mm - 2729 x 2

Rear 4 Pot
34/32mm - 1711 x 2
30/34mm - 1614 x 2
32/32mm - 1608 x 2

Hope that's useful.

Mart.

Last edited by Captain Caveman; 11-20-2020 at 03:42 PM..
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      09-27-2020, 04:46 AM   #15
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Quote:
Originally Posted by Captain Caveman View Post
I have been doing lots of research into doing a properly matched BBK retrofit, with calipers that have as close to stock piston area and front/rear bias as possible.

My first consideration was the F8X setup as it would seem a no brainer, however despite the relatively simple fitment, I've realised that the M4 has a 10% smaller total piston area than the E92 M3, which means a 10% firmer pedal with 10% less modulation, and 10% less torque at the piston.

Here are the caliper stats side by side:

E92 M3 calipers
Stock M3 piston area front 60mm - 2826 x 2
Stock M3 piston area rear 46mm - 1661 x 2
Stock M3 total area 4487
Stock front bias 63%

M4 calipers
F8X M3/M4 front BB-43 (40/40x30mm) - 2512 x 2
F8X M3/M4 rear BB-22 (44x24mm) - 1520 x 2
Total 4032 - 10% firmer - Stock bias 62%

Ideally you want to find calipers that maintain the total piston area to match the capacity of the master cylinder. If you compare the E92 specs with even the Stoptech setup, we can see that even they deliberately only differ total piston area by 1% and shift the bias slightly rearward:

Stoptech BBK
Stoptech non Trophy st60 front = 36/36/30 - 2741 x2
Stoptech Trophy ST60 32/34/36mm = 2729 x 2
Stoptech st40 355 back = 34mm 32mm - 1711 x 2
Total 4452 or 4440 x2 / 1% harder 61.5 front bias

To keep as close to stock piston area, ideally you need to find a combination of front and rear that are RADIAL mount to allow for easy bracket fabrication, NOT lug mount. Ideally with the following piston configurations, :

Front 6 Pot
32/34/38mm - 2845 x 2
30/34/38mm - 2748 x 2
30/36/36mm - 2741 x 2
32/34/36mm - 2729 x 2

Rear 4 Pot
34/32mm - 1711 x 2
30/34mm - 1614 x 2
32/32mm - 1608 x 2

Hope that's useful.

Mart.
Very, very useful information. Thank you for posting.

That being said, Stoptech is indeed a better option for the E92, than the F8X setup.
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      09-27-2020, 09:48 AM   #16
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Brake bias is function of piston area and rotor diameter. You have to multiply piston area by rotor diameter....
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      09-27-2020, 02:27 PM   #17
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Quote:
Originally Posted by marconi118 View Post
Brake bias is function of piston area and rotor diameter. You have to multiply piston area by rotor diameter....
Indeed. However matching piston area to the stock master cylinder is probably the biggest consideration for a retrofit BBK.

Brake pedal feel (soft or firm) and brake pedal travel are functions of both the brake pedal mechanical ratio and the hydraulic ratio between the area of the brake master cylinder and the total piston area of the front or rear brake calipers. Mess with this and you're in for a less than optimal setup, and either a mushy or overly firm pedal.

Obviously, brake bias can be altered with a larger disc diameter, or using pads with a higher COF, but that is an aside. For the purposes of helping folks choose the correct calipers for their retrofit BBKs, that are properly matched to the stock master cylinder, let's focus on the piston area of the calipers for the time being.

Last edited by Captain Caveman; 09-27-2020 at 02:33 PM..
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      09-27-2020, 08:08 PM   #18
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      09-29-2020, 04:12 AM   #19
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Quote:
Originally Posted by zamboni View Post
Do you need to reprogram the car after the upgrade?
No, especially not if you maintain the same F/R bias and similar piston area as stock.
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      10-08-2020, 03:26 PM   #20
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Just got back from track day at Pocono. After hitting the brakes down from 135mph to 55 it roasted my pads and rotors. SO I was thinking about upgrading to BBK.
Quote:
Originally Posted by Captain Caveman View Post

E92 M3 calipers
Stock M3 piston area front 60mm - 2826 x 2
Stock M3 piston area rear 46mm - 1661 x 2
Stock M3 total area 4487
Stock front bias 63%
...

Front 6 Pot
32/34/38mm - 2845 x 2 ...

Mart.
If I upgrade to Front 6 Pot 32/34/38mm - 2845 x 2
and keep Stock M3 piston area rear 46mm - 1661 x 2
I get a total area 4506 vs 4487
Stock front bias 63%

Is this worth it? BBK will reduce pad wear and will stop with less effort? Or is it better to upgrade to 34/36/38. Sorry I can't figure out the math on 6 pot lol
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      10-09-2020, 04:21 AM   #21
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Quote:
Originally Posted by BEATO View Post
Just got back from track day at Pocono. After hitting the brakes down from 135mph to 55 it roasted my pads and rotors. SO I was thinking about upgrading to BBK.


If I upgrade to Front 6 Pot 32/34/38mm - 2845 x 2
and keep Stock M3 piston area rear 46mm - 1661 x 2
I get a total area 4506 vs 4487
Stock front bias 63%

Is this worth it? BBK will reduce pad wear and will stop with less effort? Or is it better to upgrade to 34/36/38. Sorry I can't figure out the math on 6 pot lol
Stock E92 M3 piston area for each front caliper is 2826mm x 2.

A 32/34/38mm x2 piston area will give you a 0.67% greater piston area on the front caliper, and if you keep everything else stock, you will only increase brake torque on the front by 0.67%, whilst increasing pedal travel (slightly softer pedal) by the same amount.

The only real advantage of adding a larger caliper to the stock front disc is that it will provide a much larger pad area, which whilst only making a 0.67% improvement in overall braking force, it will allow the front brakes to absorb more heat overall as there is a greater amount of material to do so. As the brake pad itself is able to take on more heat energy, the front braking system stays cooler longer, and reduces the likelihood of the pads glazing and leaving uneven deposits on the discs that cause judder.

If you're going with bigger calipers on the front, I would encourage you to go with larger and thicker discs, which will increase braking torque whilst also provide much better heat and fade resistance on the track.

*Edit
It's important to add - one of the important elements that define the braking ability of your system, is the coefficient of friction of your brake pads. Street pads are designed to work well from cold, and and are a trade-off between overall braking performance, disc wear, noise and dust. In reality, street pads are pretty rubbish if you want excellent brakes.

Track/Race pads have an enormous tolerance to heat, and far greater COF which mean much greater stopping power, heat resistance, and less pad compression (firmer pedal) but are far more aggressive on discs, are noisy when cold and produce lots of metallic dust which can damage your wheels. Ultimately it's a trade off.

Last edited by Captain Caveman; 10-09-2020 at 04:33 AM..
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      10-09-2020, 06:23 AM   #22
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And track pads might stop worse than stock until you get enough heat in them to get into their operating range. Pad materials have operating ranges. If you are driving around town, you may not reach the low end of the range of track pads. And if you track on street pads, you may exceed the high end of their operating range.

I am not sure we know what brake issue BEATO suffered during his 155-35 slowing. Was it pads? Fluid boiling? Insufficient rotor capacity? Had he already overheated the brakes during the session? Does he use the brakes too much? Should he just try pads meant for the track first, plus a fluid change? Or is the only solution a $6000 front and rear BBK?

My take is that he is overthinking piston area. All the aftermarket kits are designed to provide similar braking force to stock. They cannot deviate much from stock because that changes bias and ABS.

Last edited by pbonsalb; 10-09-2020 at 06:31 AM..
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