Best retrofit for M3 brakes?

[Captain Caveman]

Originally Posted by Grip Addict

Why hasn't anyone figured out a way to get the 4 pot Megane Brembos on the rear yet?

I would totally jump on a retrofit BBK, but my OCD cannot have the fronts having a BBK and the back stock.

The piston area of the Megane Brembo is waaaay too big to use on the rear of the M3. If you used that caliper on the back it would massively alter the front/rear bias, shifting it rearwards enormously, and would give you a very long, mushy pedal due to the big overall increase in fluid you'd need to push to deploy the pistons.

The e92 M3 has a total rear piston area per caliper of 1661mmx2, whereas the Megane and Clio calipers have a piston area of 2512mmx2, which is 50% larger.

[Epoustouflant]

Originally Posted by Captain Caveman

The piston area of the Megane Brembo is waaaay too big to use on the rear of the M3. If you used that caliper on the back it would massively alter the front/rear bias, shifting it rearwards enormously, and would give you a very long, mushy pedal due to the big overall increase in fluid you'd need to push to deploy the pistons.

The e92 M3 has a total rear piston area per caliper of 1661mmx2, whereas the Megane and Clio calipers have a piston area of 2512mmx2, which is 50% larger.

Have you looked at the numbers on the C63 retrofit front and rear?

[Captain Caveman]

Originally Posted by Epoustouflant

Have you looked at the numbers on the C63 retrofit front and rear?

Yep. Front piston area is too big, and rear piston area is too small. Also the calipers are designed for much thicker discs, so not ideal with stock e92 discs as they are quite thin:

C63 AMG (W204) front - 34/36/38mm - 3059mm x 2 per caliper
C63 AMG rear - 28/30mm - 1322mm x 2 per caliper

The Alfa calipers front and rear are a better bet, as not only are the piston sizes a perfect match for the stock m3 master cylinder, but they are also designed for smaller discs that are closer to the stock thickness and smaller disc diameter. They would also work perfectly with M4 discs.

[Epoustouflant]

Originally Posted by Captain Caveman

Yep. Front piston area is too big, and rear piston area is too small. Also the calipers are designed for much thicker discs, so not ideal with stock e92 discs as they are quite thin:

C63 AMG (W204) front - 34/36/38mm - 3059mm x 2 per caliper
C63 AMG rear - 28/30mm - 1322mm x 2 per caliper

The Alfa calipers front and rear are a better bet, as not only are the piston sizes a perfect match for the stock m3 master cylinder, but they are also designed for smaller discs that are closer to the stock thickness and smaller disc diameter. They would also work perfectly with M4 discs.

The 6 pistons Quadrifoglio front calipers are very difficult to find though - are you referring to the 4 or 6 pots?

[Captain Caveman]

Originally Posted by Epoustouflant

The 6 pistons Quadrifoglio front calipers are very difficult to find though - are you referring to the 4 or 6 pots?

The 6-pot Brembos. Normally available in Europe on eBay and shipping shouldn't be too bad.

https://www.ebay.co.uk/itm/2018-Alfa....c100012.m1985

https://www.ebay.co.uk/itm/Alfa-Rome...0c4e%7Ciid%3A1

https://www.ebay.co.uk/itm/Big-calip...0c4e%7Ciid%3A1

https://www.ebay.co.uk/itm/2017-ALFA...0c4e%7Ciid%3A1

https://www.ebay.co.uk/itm/ALFA-GIUL...0c4e%7Ciid%3A1

Also worth noting that the Maserati caliper also has the same piston area and is also Radius mount, so that is another option (it's likely to be the same caliper tbh):

https://www.ebay.co.uk/itm/Maserati-...8AAOSweoRd3ZIP

[Epoustouflant]

Originally Posted by Captain Caveman

The 6-pot Brembos. Normally available in Europe on eBay and shipping shouldn't be too bad.

https://www.ebay.co.uk/itm/2018-Alfa....c100012.m1985

That's one of two that are available though, doesn't seem like a realistic commercial option for our cars.

[Captain Caveman]

Originally Posted by Epoustouflant

That's one of two that are available though, doesn't seem like a realistic commercial option for our cars.

The front Maserati 6-pot Brembo is identical and should be easier to source in the US. It's used on the Granturismo, Quatroporte and Ghibli and has the same 30/34/38mm piston size and is radius mount allowing for simpler custom bracket fabrication.



https://www.ebay.com/itm/Maserati-Qu...gAAOSwAiVfngzp

[Epoustouflant]

Originally Posted by Captain Caveman

The front Maserati 6-pot Brembo is identical and should be easier to source in the US. It's used on the Granturismo, Quatroporte and Ghibli and has the same 30/34/38mm piston size and is radius mount allowing for simpler custom bracket fabrication.



https://www.ebay.com/itm/Maserati-Qu...gAAOSwAiVfngzp

That's very interesting, a much better option for sure.

[W12x]

Originally Posted by Captain Caveman

The front Maserati 6-pot Brembo is identical and should be easier to source in the US. It's used on the Granturismo, Quatroporte and Ghibli and has the same 30/34/38mm piston size and is radius mount allowing for simpler custom bracket fabrication.

https://www.ebay.com/itm/Maserati-Qu...gAAOSwAiVfngzp

The Maserati one is probably the easiest to find radius mount Brembo 6 pot in the US.

How much harder is it to make custom bracket for the non-radius mount? GM have good calipers (from ZL1, other Camaros, etc) with non-radius mount, lots of them and doesn't cost much, not sure about the piston size tho.

(I remember reading somewhere on this forum that Mustang's caliper piston size isn't a good match)

[Captain Caveman]

Originally Posted by W12x

The Maserati one is probably the easiest to find radius mount Brembo 6 pot in the US.

How much harder is it to make custom bracket for the non-radius mount? GM have good calipers (from ZL1, other Camaros, etc) with non-radius mount, lots of them and doesn't cost much, not sure about the piston size tho.

(I remember reading somewhere on this forum that Mustang's caliper piston size isn't a good match)

All the GM options (ZL1, ZR1, Z06, CTS-V) use a near identical 6-pot Brembo caliper, which shares the same piston size configuration (30/34/38mm), but the spacing of the lugs make it impossible to fit with a spacer/bracket.

The only way to use these calipers is to have the lugs machined off, and then the caliper drilled to radius mount. Not a simple or cheap undertaking as it requires a precise CAD drawing of the caliper and CNC machining skills.

Much simpler and cheaper just to use a caliper that's already radius mount like the Alfa or Maserati one. Practically plug and play in comparison.

[W12x]

Originally Posted by Captain Caveman

All the GM options (ZL1, ZR1, Z06, CTS-V) use a near identical 6-pot Brembo caliper, which shares the same piston size configuration (30/34/38mm), but the spacing of the lugs make it impossible to fit with a spacer/bracket.

The only way to use these calipers is to have the lugs machined off, and then the caliper drilled to radius mount. Not a simple or cheap undertaking as it requires a precise CAD drawing of the caliper and CNC machining skills.

Much simpler and cheaper just to use a caliper that's already radius mount like the Alfa or Maserati one. Practically plug and play in comparison.

Originally Posted by Captain Caveman

All the GM options (ZL1, ZR1, Z06, CTS-V) use a near identical 6-pot Brembo caliper, which shares the same piston size configuration (30/34/38mm), but the spacing of the lugs make it impossible to fit with a spacer/bracket.

The only way to use these calipers is to have the lugs machined off, and then the caliper drilled to radius mount. Not a simple or cheap undertaking as it requires a precise CAD drawing of the caliper and CNC machining skills.

Much simpler and cheaper just to use a caliper that's already radius mount like the Alfa or Maserati one. Practically plug and play in comparison.

Thanks for explaining it!

I was just curious since GM calipers have very steady supply, and Maserati is much easier to find than Alfa but still not readily available like the American ones

[Captain Caveman]

Originally Posted by W12x

Thanks for explaining it!

I was just curious since GM calipers have very steady supply, and Maserati is much easier to find than Alfa but still not readily available like the American ones

It's doable with the GM caliper, as Slonik has shown previously, but require quite a lot of work/investment. Best bet is to use a radius mount caliper with the right piston area.

[pbonsalb]

Slonik’s 6 piston machined calipers can be combined with aftermarket 2 piece rotors and I think he offers 360 and 380 mm right options. One advantage of the “staged” BBK is that you don’t have to spend all the money up front. You can use up your stock rotors and then buy 2 piece if you will stay 360mm. I know some think they need 380mm front rotors, but in some cases it is a want rather than a need. The very highly regarded AP kit for these cars apparently works quite well on the track with 355mm fronts.

[Captain Caveman]

Originally Posted by pbonsalb

One advantage of the “staged” BBK is that you don’t have to spend all the money up front. You can use up your stock rotors and then buy 2 piece if you will stay 360mm.

Yes, this is definitely an option, but does require the use of calipers that were originally designed for slimmer discs. Using a caliper that was intended for 36mm discs on a 30mm thick disc, for example, could cause issues.

[WNS2N_T]

Originally Posted by Captain Caveman

Yes, this is definitely an option, but does require the use of calipers that were originally designed for slimmer discs. Using a caliper that was intended for 36mm discs on a 30mm thick disc, for example, could cause issues.

Like what issue/s?

Also, how/when can you determine what rotor thickness can you use on caliper that intended to use 36MM thick rotors?

Just curious..

[SAMM3Y]

Originally Posted by Maxroach

Like what issue/s?

Also, how/when can you determine what rotor thickness can you use on caliper that intended to use 36MM thick rotors?

Just curious..

I would imagine you're in danger of the piston popping out when the pad/rotor wears thin or reaching its max travel.

[pbonsalb]

30 vs 36mm would be 3mm or 0.12 inches per side. I doubt the piston would become less stable in the bore or pop out and I doubt many run their pads down to the backing plates. I suppose you could shim the pads. Some run titanium shims that would take up 1/3 of that 0.12 inches. I agree with running stuff designed to work together. You can buy rotors in various thicknesses — the Stoptech 380mm rings come in 32mm, 35mm, 38mm and maybe other thicknesses.

[WNS2N_T]

Originally Posted by Captain Caveman

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.

Really good info here.. Thank you.


Just a few questions,

Originally Posted by Captain Caveman

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%

Stock M3 piston area front is 2826 x 2 calipers, right? one piston each caliper and each side.

Originally Posted by Captain Caveman

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

And these for example, 6 pistons with 32/34/38 is 2845 x2 also per caliper?

1 caliper OEM is 60mm which is 2826

vs

1 caliper 6 pistons is 32/34/38 at 3 pistons each side is 2845, so 1 caliper is 2845 x 2 which is 5690 per caliper?

Just curious.

[WNS2N_T]

Originally Posted by SAMM3Y

I would imagine you're in danger of the piston popping out when the pad/rotor wears thin or reaching its max travel.

You will shred your pads and rotors to zero thickness before it will pop out.

[pbonsalb]

Originally Posted by Maxroach

Really good info here.. Thank you.

Just a few questions,

Stock M3 piston area front is 2826 x 2 calipers, right? one piston each caliper and each side.

And these for example, 6 pistons with 32/34/38 is 2845 x2 also per caliper?

1 caliper OEM is 60mm which is 2826

vs

1 caliper 6 pistons is 32/34/38 at 3 pistons each side is 2845, so 1 caliper is 2845 x 2 which is 5690 per caliper?

Just curious.

The calculations treat the stock single piston sliding calipers as if there is a piston on each side. Consider it a dummy piston.

[WNS2N_T]

Originally Posted by pbonsalb

The calculations treat the stock single piston sliding calipers as if there is a piston on each side. Consider it a dummy piston.

But still the same total area for OEM piston per caliper right?

Which is 2845 only, not x2 (2845 for the piston and 2845 for the "dummy sliding side"?)

[pbonsalb]

If comparing piston areas of stock sliding to aftermarket 6 piston, it’s going to be 2 sides of 1 piston compared to 2 sides of 3 pistons for the areas. Just like Captain Caveman has in his calculations quoted above.