Best retrofit for M3 brakes?

marconi118 wrote

if you upgrade from 360mm to M4 380mm or M2 comp 400mm rotors you can reduce proportionally the piston area to keep the F/R balance

Small rotor = big piston area

Big rotor = small piston area


That's why many BBK have smaller pistons than the OEM ones


I am putting Renault megane RS brembo 4 pot calipers with M4 380mm rotors on my E92 M3....
with custom brackets homemade
Best bang for the bug
or use this kit
https://freakyparts.co.uk/collections/bmw-e9x-m3-brakes/products/bmw-e9x-m3-brembo-4-pot-big-brake-kit-380mm?variant=15487394971693

400mm M2 comp rotors are too wide for megane caliper
and tooo heavy....

Makaveli7 wrote

Many useful information here - thank you all for sharing.

I retrofitted the F10m5 brakes and had zero issues, sold them to a friend who also have no issues with them whatsoever. The major downside was at the beginning I had to fit 20" M359s and then proceeded to grind the calipers for less than a mm to fit the oem m359 with 15mm spacers...

Captain Caveman wrote

Hey, that's very interesting! What size discs were you using - 400mm? I was under the impression that 380mm was the largest you could fit under ZCP, so this is VERY encouraging! I had an idea that at least 390mm disc would fit on the front with a 6-pot Brembo caliper and ZCP with no issues.

Be good to know more about your setup.

Makaveli7 wrote

Was running the F10m5 disks - 400mm F&R...

You can see the clearance is like 1mm in the front. Please note that I did grind the calipers around 1mm on the 2 corners to get them to clear (nothing that might cause any issues)

Captain Caveman wrote

Thanks, that's immensely useful! Do you think the M5 Brembo caliper is larger than the normal Brembo GT6 caliper? It looks fatter to me?

Makaveli7 wrote

Both are almost the same - The GT6 is more defined. We actually tried to cnc an F10 caliper to for the look of the GT6 and it actually worked (No pics at the moment)

Captain Caveman wrote

Yes, but only if you increase the rotor diameter proportionally.

The Megane Brembos have 40/40mm x 2 =2512mm x 2 piston area per caliper which is 11.1% smaller than the stock front E92 caliper.

Increasing the disc size from 360 to 380mm is only a 5% increase in disc size, so the piston area reduction is greater than the corresponding increase in disc diameter.

Also, and importantly - increasing the disc diameter will offset the torque loss caused by the smaller piston area (by the % increase in disc diameter), but it WILL NOT offset the resulting change to pedal travel, firmness/softness and modulation.

The Megane Brembo will give you a 11% firmer pedal and 11% less travel and potential modulation.

Just saying.

Captain Caveman wrote

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.

AzRiz wrote

Great info there mate.

What would your opinion be on upgrading just the front calipers to a 30/34/38 mm piston caliper and using them on the standard 360mm discs?

By my calculations, the total piston area is 97.22% of the stock piston size - do you think this will result in a noticeable difference in pedal travel, feel, or significant change in braking torque or bias?

At a guess, a 2.78% difference will probably be unnoticeable and upgrading the pads up from the standard Brembo ones to PFZ pads or something will make up for the tiny difference.

I know a few people who have used the C63 AMG caliper which has piston sizes of 34/36/38mm - meaning a total piston area increase of 8.22% - and they report no noticeable change in pedal travel/feel and are very happy with the results. Based on this, I'm hoping that a 2.78% reduction will not be a negative thing, or even noticeable.

Would be interested to hear your thoughts.

Captain Caveman wrote

This is very close to stock piston area as you say, so will only make the pedal marginally shorter-travel/firmer than stock, probably to your advantage if u prefer a firmer, more reassuring pedal.

Here are the calcs with the new fronts and stock rears:

30/34/38mm - 2748mm x 2
46mm rear - 1661 x 2
Total piston area 4409 - 1.74% smaller than stock
Front/Rear bias 62.3% front bias - so 0.7% more rear bias

It's worth stating that there is very little benefit to simply enlarging the caliper without also increasing the disc thickness and diameter. Sure, the larger pad will have greater heat resistance than the smaller pad, however the disc will be the limitation here.

The smaller piston area of the new caliper with everything else the same will actually give you less clamping force.

I am guessing the caliper you are considering is either the Porsche/Brembo 18Z or the Maserati/Alfa Romeo Brembo caliper?

The larger piston area of the W204 C63 Brembo caliper will give you slightly longer pedal travel and a slightly softer pedal, however will provide greater clamping force.

Most BBK makers tend to opt for a smaller piston area than stock to allow for the additional torque provided by a larger disc diameter, so if you ever plan to track your car or are likely to go with a larger disc at some point, it's worth going for the smaller piston area to be safe.

For example, lots of people are fitting the M4 setup which has about 10% smaller piston area, but larger discs all round.

Hope that helps!

AzRiz wrote

Thanks for your input there.

Yes it is indeed the Alfa Romeo caliper that I'm looking at.

In all honesty, the biggest motivator for this change is simply aesthetics. I'd like to get the brakes looking better as long as there is no noticeable/significant degradation in braking performance.

My reason to consider this caliper instead of the AMG one is mostly due to the piston sizes (97.22% of stock rather than 108% like the AMG is) and the other, much less important reason, is that the caliper is slightly better looking than the AMG one.

The Alfa caliper is also designed to fit on a 360mm disc in on the Alfa itself which is spot on here, and hence why I'm not looking to increase the disc size (I would use the M4 380mm disc but I don't believe that this is a good idea if the caliper and pad are sized/curved to a 360mm disc).

I'm struggling to decide whether it's better to use the AMG caliper with a 108% piston area and the consquences that come with that, or is it better to use the Alfa caliper at 97.22% because the 2.78% change should hopefully be unnoticeable...

Captain Caveman wrote

There is normally some tolerance for a given caliper size, so the Alfa Brembo caliper should work with the larger 380mm M4 discs without issue.

Other big problem is the AMG caliper is designed for a 36mm thick disc, whereas the Alfa disc is 32mm. As the stock M3 disc is only 30mm, I would advise against going with such a big thickness difference, as their is a risk of the pistons popping out of the caliper. Calipers are designed for only small thickness ranges.

The other difference between the AMG caliper and Alfa caliper is pad size. The alfa uses a comparatively small pad compared with the AMG, so they will wear faster and have less heat resistance. You want a pad height that will sweep the full disc height without overlap or unswept area.

Stock M3 front pad:


Alfa pad:



AMG pad:

AzRiz wrote

I did look at the pad differences and my plan was to paint the inner 8mm (65-57) of unswept area that the Alfa pad would cause. It's not ideal but if it's the better caliper to use, it should be fine.

I also did look at the disc thickness comparisons and I think that it wouldn't be an issue to use a 30mm disc if the caliper usually uses 32mm. Going from 36>30 doesn't sound like a great idea, though.

Would you personally up it to a 380mm disc, despite keeping stock rears? 380mm is a 5.56% increase on a 360mm disc - is it fair to relate that figure to the 2.78% reduction in piston area (and therefore the clamping force) and say that the final brake torque over the stock setup is approximately 5.56-2.78 = 2.78% increase?

One other issue with using a 380mm disc is then that according to PFC, the M4 pad height is 71mm which will leave an even bigger ring of unswept area. This is obviously fine if it's the better setup to use, though, can just paint it.

Captain Caveman wrote

If you go with the M4 discs, the 2.7% reduction in piston area, combined with the 5% increase in disc diameter will net you a 2ish % increase in overall front brake torque, and a slight increase in front bias.

In terms of swept area, there are 2 pad heights available for the Alfa Brambo caliper; D1116 which has a 55mm annulus and D1666 which has a 65mm annulus. You should be able to get the right swept area with one of these.

AzRiz wrote

Thanks for this mate, I spent a while trying to find this D1666 pad but can't seem to find any real info about it. Would ideally love to get a good fast-road pad that is 65mm tall.

Have you found any specific pads yourself that are 65mm tall for the Alfa caliper?

If not I'll have to go with the 57mm pad and paint the 8mm as originally planned.

What is most likely going to be your final choice of brakes, by the way? Have you decided yet?

Cheers
Az

marconi118 wrote

any cheap source for the Alfa caliper?