Anyone running Z17 or Z18 Brembo BBK Kit? Thoughts?

[crow4213]

Can we see the rears as well? I want to see what a 360mm front rotor and 328mm rear rotor look like together.

Here is a crappy cellphone pic of the back and front together.

[heinzboehmer]

Yes there is unsprung mass to be removed. You can get a few lbs per corner doing wheels / brakes. But depends on what options you go with and whether the net result will be loss of mass or not. Larger rotor increases mass and could be offset with lighter caliper. Sometimes it's a wash, sometimes it net increases mass. For example, 996 rear caliper with bracket and pads is around 6.8 lbs, while stock cast iron is 9 lbs, while Stoptech 355 bbk rear caliper/bracket/pads was around 11 lbs.

To add, moment of inertia of a cylinder goes up linearly with mass but quadratically with radius. So even a lighter rotor with a larger radius will not necessarily result in more response at the wheels. Not to mention that most larger rotors are heavier.

But yeah totally agree with you, moving to a BBK is not necessarily going to change unsprung mass/rotational characteristics at the wheels in a favorable direction. Lots of factors that need to be considered.

[mrgizmo04]

YMMV, but I would bet most prepped E46s could benefit from moving the bias back slightly. Track suspensions don't allow nearly as much dive, leaving more traction in the rear to take advantage of.

Of note, rotor diameter is not a big factor in bias.

I'm not aware of pad tapering being an issue on this platform, and I talk to a lot of 991 GT3 owners who track their cars.

On the 3 points above.

The problem with options being discussed in this thread on the latest Brembo donor car discoveries is that they move the bias forward. I'm with you on slight rearward adjustment. I'm actually quite enjoying 996 kit even after dropping weight at the rear of the car.

Rotor diameter is not a negligible contributor. While it does contribute at 1/2 the diameter increase and piston contributes a square term, it can not be disregarded. If CSL didn't increase front rotor to 345, bias would drop ~2% to close to 62%. A lot of variables at play, which inclides rotor, piston bores, pad mu, etc.

GT3 guys got smarter over time and learned that pads that can take proper heat are a must upgrade. Rolling off the dealership floor and going straight to the track resulted in tapering when the street pads on their cars melted and tapered. Their caliper and attachment is super sturdy and their entire systems were designed for the car. Have you seen those washers/spacers that get included with the brackets to mount whatever Brembo calipers on our cars? I would not say that is a sturdy design for when you really need your braking system. These retrofits are a concern, but as I said before, just doing street driving might be ok.

Haven't heard of AP issues with taper, as I don't follow them too closely, but interesting. They are seen as the creme of the crop, so that must be annoying.

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[r4dr]

Food for thought. Most can ignore this post.

These options all look interesting until you start looking at the details. For anyone street driving, what I say can probably be disregarded. Let's all just accept that 99+% of the folks looking at 6pot, or other 4pot "upgrades" are doing it for looks. Nothing wrong with that.

I am semi happy with 996 kit for street and track. Read, this is where the bias and feel and power actually come into play, when you are hauling 130 mph down a straight and need to nail down a turn slowing down at the limit to around 45 mph to navigate a corner to stay on track and not eat gravel for lunch.

Can all these sellers make any caliper fit onto any rotor. Sure. Make a bracket with the right offset to center around whatever common size E46 rotor being used CSL 345x28 or e9x 360x30. Should we put those kits onto our cars. I'm not sure.

I'm with you so far.

Most of these options will put brake bias to around or even over 70% (assuming paired with popular e46 rear options of stock/CSL/996). Does it matter for street driving? Not so much. In an emergency when you slam the brakes, you will stop, ABS/DSC will save you. For those trying to drive at the limit, that bias is not ideal as that affects all aspects of handling when working the car on entry, and makes a difference whether you stay on track or plow into a wall.

YMMV, but I would bet most prepped E46s could benefit from moving the bias back slightly. Track suspensions don't allow nearly as much dive, leaving more traction in the rear to take advantage of.

Most of these kits come from much heavier cars, and have to put out a lot of stopping power via 3x smaller pistons (6pot) or 2x larger (4pot), but where they are appropriately paired with their rear brakes on those cars. Putting these front only options on our cars makes them suboptimal.

Touareg option uses 2x 46mm pistons. That is a lot of volume to pump to front brakes. You will get longer pedal travel with our MC. As an example of more proper piston and power sizing, take ST40 kit which uses 42/38 pistons on 355 rotor, 996 uses 40/36 on 345 rotor (a bit underpowered on its own).

Agreed on people ignoring piston volume vs. master cylinders. One car using much larger pistons with a more generous MC will feel very different than a car using the same pistons and an undersized MC. Based on feedback and my personal experience driving a Z4M with the swap, I would hypothesize that the piston area on the Megane kit would be as far as you want to go without looking upstream to the MC. Of note, rotor diameter is not a big factor in bias.

Using same piston sizes from trailing and leading on front of the car when performance driving is very suboptimal, as the pad starts tapering and you get poor pedal feel (proper sizing is to have larger piston trailing). I think same size piston is also the problem with Megane caliper (and maybe the DB9, although this specific one I don't remember). So some of these options are not meant for proper performance driving and track use.

This might be true in theory, but the reality is more complicated. I don't have any evidence for E46M with Megane, but I will say that the 991 GT3 uses 3x 30mm pistons up front with quite a large pad. I'm not aware of pad tapering being an issue on this platform, and I talk to a lot of 991 GT3 owners who track their cars. Relative piston size might be one part of the equation, but friction material and overall caliper stiffness + design also play large parts.

Another data point: AP Radicals use staggered piston sizes. You should ask SYT_Shadow about his thoughts on tapering in those calipers

ZL1 uses 38/34/30 pistons, AMG uses 38/36/34. Also more total volume of fluid, longer pedal travel and more clamping front bias around 70%. My rough calc is ZL1 69% bias and AMG is closer to 72%.

Another problem is that most of these calipers on these donor cars come with x32 or x34 or even x36 mm wide rotors. Can these sellers find the midpoint for how to fit calipers on E46 with the right mounting bracket/adapter? Sure, that's why they are selling it. They heard the forum/Facebook/Insta hype and craze of putting Brembros on E46, so they are filling the gap in the market. Do I want to run any of those options on a x28 CSL rotor or even a x30 E9x rotor. Probably not. I don't want to have the pistons protruding halfway out with brand new pads and then run the risk of popping them on track when my pads run to the backing plate. Unless these guys pair these kits with proper thickness pads (much thicker than comes on those donor cars), but I suspect they are not offering that . Most standard pads are 16-17mm thickness.

Very valid. I will say the Megane caliper maxes out at 30mm, so I wouldn't hesitate to run a regular D1001 pad to its backing plate on the 28mm ZCP rotor. It's close enough. But that Mercedes caliper on a 28-30mm rotor is scary.

[mrgizmo04]

Here is a cool online brake analyzer to see how your new rotor size, caliper pistons and pad height will impact bias, pedal effort, etc.

https://upbrakes.com/upgrade_advisor

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[mrgizmo04]

More info is always welcome 👍.

I won’t claim to be fast. I experienced a little bit of fade coming down a twisty mountain a couple weeks ago, same as I got on my Z3’s worn out brakes several years ago. Fluid flush and new pads took care of that then, and it likely will now.

I suppose it’s too early for me to be thinking about brake upgrades. Not once during an autocross have I had a brake issue. The front tires are the LIMFAC right now.

I appreciate all the insight on why rotor width matters, why piston size difference matters, etc. It all makes a lot of sense. I never really thought I needed big 6-pot calipers, but the 4-pot options have always been enticing.

One question: is there a significant weight advantage to these 4-pot calipers? I am not interested in reducing sprung weight in my car much except for the sun roof somewhere down the line, but unsprung weight reduction…

My job is done when I get 1 person to understand they don't need a bbk ✋.

Yes there is unsprung mass to be removed. You can get a few lbs per corner doing wheels / brakes. But depends on what options you go with and whether the net result will be loss of mass or not. Larger rotor increases mass and could be offset with lighter caliper. Sometimes it's a wash, sometimes it net increases mass. For example, 996 rear caliper with bracket and pads is around 6.8 lbs, while stock cast iron is 9 lbs, while Stoptech 355 bbk rear caliper/bracket/pads was around 11 lbs.

Have to do some research to find those numbers, hopefully someone has run the parts on their car and weighed them, or look for manufacturer specs.



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[nahvkolaj]

More info is always welcome 👍.

I won’t claim to be fast. I experienced a little bit of fade coming down a twisty mountain a couple weeks ago, same as I got on my Z3’s worn out brakes several years ago. Fluid flush and new pads took care of that then, and it likely will now.

I suppose it’s too early for me to be thinking about brake upgrades. Not once during an autocross have I had a brake issue. The front tires are the LIMFAC right now.

I appreciate all the insight on why rotor width matters, why piston size difference matters, etc. It all makes a lot of sense. I never really thought I needed big 6-pot calipers, but the 4-pot options have always been enticing.

One question: is there a significant weight advantage to these 4-pot calipers? I am not interested in reducing sprung weight in my car much except for the sun roof somewhere down the line, but unsprung weight reduction…

[mrgizmo04]

Another important point I forgot to mention about piston overextension and the fact that most of these calipers are designed for much thicker rotors and this is a BIG ONE.

It is safety. So calipers are made with pad limiters or these brackets that hold the pad in place so it doesn't slide forward with the rotor rotation. These limiters are sized to almost touch the rotor surface, with few mm to spare in case bearings flex, allow for thermal expansion, etc.

Well, under properly designed setup (i.e. running them on the corresponding donor cars), they will ensure that when the pad gets to the backing plate, that the backing plate will not simply fall out or slide out with rotor rotation. Backing plates are usually 4-5mm thick.

Running thinner than designed rotors creates space between the pad limiter bracket and rotor surface. That means that as the pad starts wearing, and way before it gets close to the backing plate, the pad can slide forward and jam the rotor, or simply fall out/slide out.

This is not only, but also why, there is a recommended minimum thickness of rotors even for oe setups, outside of the rotor metal just getting thinner and potentially crumbling.

Pic attached for nomenclature of what I'm talking about as example on 996 caliper.

These "BBK upgrades" become a pretty bad idea for street/looks cars, since you don't check for wear frequently.

So as long as starting gap per side is bigger than thickness of the backing plate (4-5mm) + few mm of extra clearance between caliper pad limiter to rotor, that is very concerning (at least to me). Like caliper designed for 34mm and running it with 30mm e9x rotor. Definitely bad running CSL 28mm rotor. Running AMG calipers which are made for 36mm(?) on any of the options avail for E46...

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[heinzboehmer]

996 front kit for our cars come off x28 rotor size on Porsche, which is same as our stock 325x28 or CSL 345x28, so yes, not a problem.

996 rear kit for our cars comes off (I believe, but don't remember) x22(?) rotor size on Porsche, which is different from our stock/CSL size of 328x20. That said, I am more comfortable running this setup in rear given less load in rear and less than likely scenario of running those pads to backing plates. And swapping pads street to track every event I see the progression. Less that ideal replacing these pads before the meat is gone, but again, rear wear is less than front.

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Good to know about the rears. I'll keep an eye on them. Also swap out pads before/after every event, so no big deal.

[mrgizmo04]

996 rotors are x28, right? So no concern about piston overextension with those.

996 front kit for our cars come off x28 rotor size on Porsche, which is same as our stock 325x28 or CSL 345x28, so yes, not a problem.

996 rear kit for our cars comes off (I believe, but don't remember) x22(?) rotor size on Porsche, which is different from our stock/CSL size of 328x20. That said, I am more comfortable running this setup in rear given less load in rear and less than likely scenario of running those pads to backing plates. And swapping pads street to track every event I see the progression. Less that ideal replacing these pads before the meat is gone, but again, rear wear is less than front.

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[mrgizmo04]

Also I decided on pairing it with the 996 rears knowing they push the bias towards the rear so i thought they would play nice with each other.

There are spreadsheets that you can use to calculate bias for you or to see impact, they can handle multi piston setups.

996 rears move the bias rearward ONLY IF paired with a front setup that provides less clamping force than stock fronts, like the 996 fronts.

996 rear vs stock rear, 996 provides less clamping force.

Running stock M3 fronts with stock M3 rears gives 66.87% bias, but running stock M3 fronts with 996 rears gives 67.89% bias because 996 rear clamping force is overall weaker, so bias moves forward.

To even out the high clamping force of AMG fronts, you would be better off running CSL rear which runs 46mm rear piston. Stock rear runs 42mm piston, 996 runs 28/30 pistons (but because of radius squared term those 2 pistons together have smaller piston area than a stock 42mm).

So your AMG setup yield the following front bias paired with:
stock M3 rear 70.74%
CSL rear 66.84%
996 rear 71.70%

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[heinzboehmer]

"But I want to do a track day." We all overestimate our abilities, that is just human nature. Don't upgrade your equipment beyond/before your driver skills. Go see what you can do with what you have. Plenty of fast guys running stock setups and they work decently.

I'm not fast at all, but agree. Running stock (non-ZCP) setup on the track with track pads and it's more than enough.

That being said, I'm moving to 996 calipers soon because I hate swapping pads on the stock ones. 996 rotors are x28, right? So no concern about piston overextension with those.

[crow4213]

Can we see the rears as well? I want to see what a 360mm front rotor and 328mm rear rotor look like together.

I'll take some pics next time it's out of the garage.

[crow4213]

Food for thought. Most can ignore this post.

These options all look interesting until you start looking at the details. For anyone street driving, what I say can probably be disregarded. Let's all just accept that 99+% of the folks looking at 6pot, or other 4pot "upgrades" are doing it for looks. Nothing wrong with that.

I am semi happy with 996 kit for street and track. Read, this is where the bias and feel and power actually come into play, when you are hauling 130 mph down a straight and need to nail down a turn slowing down at the limit to around 45 mph to navigate a corner to stay on track and not eat gravel for lunch.

Can all these sellers make any caliper fit onto any rotor. Sure. Make a bracket with the right offset to center around whatever common size E46 rotor being used CSL 345x28 or e9x 360x30. Should we put those kits onto our cars. I'm not sure.

Most of these options will put brake bias to around or even over 70% (assuming paired with popular e46 rear options of stock/CSL/996). Does it matter for street driving? Not so much. In an emergency when you slam the brakes, you will stop, ABS/DSC will save you. For those trying to drive at the limit, that bias is not ideal as that affects all aspects of handling when working the car on entry, and makes a difference whether you stay on track or plow into a wall.

Most of these kits come from much heavier cars, and have to put out a lot of stopping power via 3x smaller pistons (6pot) or 2x larger (4pot), but where they are appropriately paired with their rear brakes on those cars. Putting these front only options on our cars makes them suboptimal.

Touareg option uses 2x 46mm pistons. That is a lot of volume to pump to front brakes. You will get longer pedal travel with our MC. As an example of more proper piston and power sizing, take ST40 kit which uses 42/38 pistons on 355 rotor, 996 uses 40/36 on 345 rotor (a bit underpowered on its own).

Using same piston sizes from trailing and leading on front of the car when performance driving is very suboptimal, as the pad starts tapering and you get poor pedal feel (proper sizing is to have larger piston trailing). I think same size piston is also the problem with Megane caliper (and maybe the DB9, although this specific one I don't remember). So some of these options are not meant for proper performance driving and track use.

ZL1 uses 38/34/30 pistons, AMG uses 38/36/34. Also more total volume of fluid, longer pedal travel and more clamping front bias around 70%. My rough calc is ZL1 69% bias and AMG is closer to 72%.

Another problem is that most of these calipers on these donor cars come with x32 or x34 or even x36 mm wide rotors. Can these sellers find the midpoint for how to fit calipers on E46 with the right mounting bracket/adapter? Sure, that's why they are selling it. They heard the forum/Facebook/Insta hype and craze of putting Brembros on E46, so they are filling the gap in the market. Do I want to run any of those options on a x28 CSL rotor or even a x30 E9x rotor. Probably not. I don't want to have the pistons protruding halfway out with brand new pads and then run the risk of popping them on track when my pads run to the backing plate. Unless these guys pair these kits with proper thickness pads (much thicker than comes on those donor cars), but I suspect they are not offering that . Most standard pads are 16-17mm thickness.

Just my $0.02.

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All very god points and I agree almost fully. I never intend on tracking my car and got it mainly for looks. That being said, the feel of pedal in my mind has not been affected at all and if it has it's been negligible. I am currently braking the pads in and they recommended no hard stop for the first 500 miles, but a couple of times by accident Ive pressed on the pedal and the car came to a stop much quicker than anticipated. Also I decided on pairing it with the 996 rears knowing they push the bias towards the rear so i thought they would play nice with each other.

I dont think i would recommend this setup to anyone actively looking to track their car but my expectations have been blown away on the street so far. Also good point on the rotor size differences and this is something i'll always be wary of, probably replacing pads at more than half life left just to avoid this situation.

[mrgizmo04]

I want to make it very clear, I am not dissuading anyone from pursuing any of these options. I just want to make sure that folks understand the potential implications beyond finding cheapest price, or sexy marketing language on "best", or list of benefits from "upgrading".

Easy pad changes and additional thermal capacity are not benefits I see for those street driving, who can make their current setups/pads last for several years.

"But I want to do a track day." We all overestimate our abilities, that is just human nature. Don't upgrade your equipment beyond/before your driver skills. Go see what you can do with what you have. Plenty of fast guys running stock setups and they work decently.

For Brembro bling chasers, you don't have to worry about my comments as you probably won't get to the limits of those setups to experience them. Find what looks good to your eyes.

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