Front Brake Rotor Weights and Technical Details: Euro CSi

[Auraraptor]

Brembo’s 2 piece 332mm GT brake kit weighs 7.62kg vs ~9.5kg for the OEM 322mm disk (per my old notes).

Does anyone have the Euro CSI 345mm weight? I had heard it was around 9kg but no confirmation is available. Are the rotor specs (beyond diameter, but not the offset/height) known?

CSi L: 34112227735 R:34112227736

[Fatandre]

Brembo’s 2 piece 332mm GT brake kit weighs 7.62kg vs ~9.5kg for the OEM 322mm disk (per my old notes).

Does anyone have the Euro CSI 345mm weight? I had heard it was around 9kg but no confirmation is available. Are the rotor specs (beyond diameter, but not the offset/height) known?

CSi L: 34112227735 R:34112227736

Shame that the CSI calipers are so damn heavy.

[Tx850ci]

Why bother? My Zimmermann cross drilled rotors came in. Used them before and they work great. I have zero concern about what a part weighs on a 2 ton German behemoth including sprung weight. It won’t make a wit of difference on how the car rides or performs.

[Auraraptor]

We must have different driving habits… The factory set up on non-CSi cars is consistently poor (or if you will ‘conservative’). Minor tweaks really helped make the various e31s I have owned over the decades much more direct and engaging.

Having used everything from 16, 17, 18, and 19in wheels across a range of tires….yes weight matters and 2lb unsprung can definitely be felt

There is no reason any E31 should handle and brake any worse then a Ferrari 456. They weigh nearly the same.

The computer that used to have my technical data is long gone…. And I figured someone has it. Courtesy of hyper I’m using a temporary front to balance my rear… I’m trying to settle on a long-term solution and deciding between options

[CD05001CIA]

Why bother? My Zimmermann cross drilled rotors came in. Used them before and they work great. I have zero concern about what a part weighs on a 2 ton German behemoth including sprung weight. It won’t make a wit of difference on how the car rides or performs.

I have driven a stock 1991 8series, a stock 1996 8series w/EDC, and a modified 1995 8series with what seemed to be the best combination of spring, sway bar, camber plate, re-valved shock etc. Night and day difference.

The 1995 was THE ONE.

[m6bigdog]

FWIW: The BMW ETK (Electronic Parts Catalog) has a weight specification for all components in the vehicle.

E31 & E34 Euro Front Brakes:
34 11 2 227 735 Front Rotors, Left, 345x32 - 20 Lbs
34 11 2 227 736 Front Rotors, Left, 345x32
34 11 2 227 115 Caliper Left - 14.8 Lbs
34 11 2 227 116 Caliper Right

From my data: the front E31 Euro CSi suspension unsprung weight is 126 lbs; to include a wheel that weight 50 lbs.
Rim and tire weight are a significant variable as the larger the rim (18 vs 17" and wider the rim and tire the more the wheel weighs.
Sacrificing rim and tire width to reduce unsprung weight is a pursuit in search of the misunderstood. As Tire patch is everything!
IMHO, rotor and caliper weight generate the same result; as you will not feel a few pounds difference from brake weight with a +/- 126 lb unsprung weight.
Also, the rotor disc weight (more is better) is everything for reducing rotor temperature rise.
Yep the cooling fins are important, however without the rotor mass the fins are useless.
I would be less concerned with the rotor and caliper weight and be more concerned with the using directional fin rotors, correct pad compound and F/R brake bias.

[Auraraptor]

Fixing bias for a rear kit I’m designing is the motivation.
Disk weight is an art…you don’t want too light as then you have no thermal mass.
I would argue duct work is also critical when optimizing for a heavy car
A few lb is a big deal when it’s x4 but agree you won’t feel it w a standard csi setup because the caliper weight increase counters the rotors
For CSI calipers, at least historically, pad selection was not the best
Due to both of the above, I have no intention to use them.
Thanks for the info

[m6bigdog]

Fixing bias for a rear kit I’m designing is the motivation.
Disk weight is an art…you don’t want too light as then you have no thermal mass.
I would argue duct work is also critical when optimizing for a heavy car
A few lb is a big deal when it’s x4 but agree you won’t feel it w a standard csi setup because the caliper weight increase counters the rotors
For CSI calipers, at least historically, pad selection was not the best
Due to both of the above, I have no intention to use them.
Thanks for the info

IMHO:
There is nothing "ART" about vehicle suspension dynamics and brake performance design.
It is all about engineering for the physics of ground vehicle suspension dynamics.
If a few pounds of unsprung weight affects E31's ride quality and performance, I submit there are other suspension problems.

The E31 comes with more brake ducting than most vehicles and I would surmise that rotor thickness and directional fins (moving air through the rotor) are the primary engineering attribute for cooling the rotor.
Also, make sure the rotor fin intake is compatible with the installed backing plate. BMW semi-floating rotors draw air from both sides of the disk.
Also, I run BMW "directional" turbine wheels that flows plenty of air to the rotors; more than a passive duct modification would ever provide. BMW claimed near 20% reduction in rotor temp.

At 126lbs for the front axle unspring weight and a laden sprung weight of 993 lbs: the 12% unsprung weight would indicate you could virtually eliminate the unspring brake weight and not change the vehicle ride quality or cornering performance. Except you have no brakes!!
Also, the rear unsprung weight is greater than the front at approximately 150lbs with a rear sprung weight of 960lbs. Now what? with rear brakes at only 23lbs, an even smaller fraction of the unsprung weight and there is no way to reduce this weight without reducing the wheel size.
Unfortunately vehicle cornering and stopping performance are performance factors bound by vehicle weight and tire patch.
Since vehicle total weight is difficult to reduce in any significant way, we are left with increasing the tire patch to increase the traction needed for added performance and the more tire patch, the wider the tire width on a wider rim and more is then adds to unsprung weight!!
Pretty much a circle of demise, weight is the problem and performance parts add weight no matter what!
The tire natural frequency and damper performance are the engineering factors greater than the 10-20lbs of unsprung weight.

For those that think the Euro CSi Big Brakes are too heavy you would never consider buying a E60 late model M5.
Why, because the 374x36mm front (aluminum hat, directional fin and perforated) rotor weights in at 29lbs; that is only 4 lbs less than the total weight of the Euro CSI 345x32mm Rotor and massive 4 piston ATE cast iron Caliper!!
If that rotor weight was such a ride quality and performance degradation factor BMW M Division engineers would have done something else.
However, of you have ever driven a E60M5 I anticipate you would want one.

As for the Euro CSi Textor brake pad selection:
The only pads BMW has supplied are the Textar 4056 front and 4057 rear pads.
IMHO, they are an ideal pad compound for aggressive street performance with only a slight cold pad reduction in coefficient.
I have been using these CSi brakes and pads on my 91M5 and 850 for over 25years and they are quite and fade resistant.
I know individuals that track their BMW's with these brakes and the Textar pads performed better than any custom performance track pads they could come up with.
Yep, the Euro CSi are expensive (unobtainium at this point) but that is not a reason to doubt there excellent aggressive street performance.
Are there better brakes always, carbon-ceramic brake rotors would save half the rotor weight however you could buy another E31 for the cost of a 4 wheel carbon-ceramic brake kit.

[Fatandre]

I have the CSI calipers and was wondering if there are any good aftermarket discs available. Any idea?

[TxGR8White]

The “butt-dyno” is not an accurate measuring device…

I heard you can save a few pounds by evacuating the Freon from the A/C system…

[m6bigdog]

I have the CSI calipers and was wondering if there are any good aftermarket discs available. Any idea?

The Euro E39-M5 uses a similarly dimensioned Aluminum hat semi-floating rotor except without the 18mm hub pins.
In the US that rotor is an all cast version that weighs 3lbs more.

[Auraraptor]

IMHO:
There is nothing "ART" about vehicle suspension dynamics and brake performance design.
It is all about engineering for the physics of ground vehicle suspension dynamics.
If a few pounds of unsprung weight affects E31's ride quality and performance, I submit there are other suspension problems.

The E31 comes with more brake ducting than most vehicles and I would surmise that rotor thickness and directional fins (moving air through the rotor) are the primary engineering attribute for cooling the rotor.
Also, make sure the rotor fin intake is compatible with the installed backing plate. BMW semi-floating rotors draw air from both sides of the disk.
Also, I run BMW "directional" turbine wheels that flows plenty of air to the rotors; more than a passive duct modification would ever provide. BMW claimed near 20% reduction in rotor temp.

At 126lbs for the front axle unspring weight and a laden sprung weight of 993 lbs: the 12% unsprung weight would indicate you could virtually eliminate the unspring brake weight and not change the vehicle ride quality or cornering performance. Except you have no brakes!!
Also, the rear unsprung weight is greater than the front at approximately 150lbs with a rear sprung weight of 960lbs. Now what? with rear brakes at only 23lbs, an even smaller fraction of the unsprung weight and there is no way to reduce this weight without reducing the wheel size.
Unfortunately vehicle cornering and stopping performance are performance factors bound by vehicle weight and tire patch.
Since vehicle total weight is difficult to reduce in any significant way, we are left with increasing the tire patch to increase the traction needed for added performance and the more tire patch, the wider the tire width on a wider rim and more is then adds to unsprung weight!!
Pretty much a circle of demise, weight is the problem and performance parts add weight no matter what!
The tire natural frequency and damper performance are the engineering factors greater than the 10-20lbs of unsprung weight.

For those that think the Euro CSi Big Brakes are too heavy you would never consider buying a E60 late model M5.
Why, because the 374x36mm front (aluminum hat, directional fin and perforated) rotor weights in at 29lbs; that is only 4 lbs less than the total weight of the Euro CSI 345x32mm Rotor and massive 4 piston ATE cast iron Caliper!!
If that rotor weight was such a ride quality and performance degradation factor BMW M Division engineers would have done something else.
However, of you have ever driven a E60M5 I anticipate you would want one.

As for the Euro CSi Textor brake pad selection:
The only pads BMW has supplied are the Textar 4056 front and 4057 rear pads.
IMHO, they are an ideal pad compound for aggressive street performance with only a slight cold pad reduction in coefficient.
I have been using these CSi brakes and pads on my 91M5 and 850 for over 25years and they are quite and fade resistant.
I know individuals that track their BMW's with these brakes and the Textar pads performed better than any custom performance track pads they could come up with.
Yep, the Euro CSi are expensive (unobtainium at this point) but that is not a reason to doubt there excellent aggressive street performance.
Are there better brakes always, carbon-ceramic brake rotors would save half the rotor weight however you could buy another E31 for the cost of a 4 wheel carbon-ceramic brake kit.

There most definitely IS an ART to selecting the best braking solution for your needs. The optimal brakes for an endurance racer vs a track car vs an autocross car vs a high speed GT cruiser vs a mixed use road car vs a city car are quite different. Further factor in budget and user end goals and you are most definitely balancing competing factors....that is an art.

That leads to the question: what are my end goals?

As as mentioned, there is no reason the E31 should perform inferiority in terms of handling and braking vs a 456. The cars weight nearly the same (+/-3-4% gross difference in weight). Using matched tires the 456 still will out turn and out brake a standard E31 all day / every day (assuming the 456 actually running of course). My goal is to make my E31 exceed that benchmark with an additional caveat: What would BMW have done if they actually gave a damn about the E31 instead of forgetting it circa late 90s.

So to summarize:
(1) Period correct**
(2) Fit under most 18s
(3) bench-marked vs the 456 (ie high speed GT w light track use)
**The only area I am willing to forgo period correct is consumables like tire compound and brake pads (more on that later).

Again this is just for me/my needs....I have no intention of marketing/selling anything. This is literally a side project to distract my from work, but to hit your major points:

Stopping distance/Tires: As you know brakes are merely the conduit for braking fluid and the REAL stopping occurs as a function of the tires. On my E31 I am using semi-race 200 tread wear tires with good first lap performance on my E31 (aka they have high grip even at a very lukewarm temperature). For this, I sacrifice tire life/mileage (a lot), noise (a fair bit), and ride (a moderate a bit), and cost (a minor bit) for this but in an emergency braking system for a car I only drive on weekends, they are worth it. That said for most drivers it takes consecrated effort to actually cause the tires to break traction under hard braking (which would make sense given their extreme grip levels). This combined with (IMHO) the sub-optimal brake bias drove this project.

Thermal capacity: Obviously of the rotors is essential. You can go too light...15 years ago there was a company that essentially adapted motorcycle rotors to Caterhams/ultralights/Lotus 7, touting massive weight savings. It definitely was true BUT your brakes would last maybe 15 minutes at most before even the best fluid would boil over....for obvious reasons, no thermal capacity! For this reason I am looking nearly exclusively at 30-34mm thick rotors F and 28-30 rears. My prototype rear kit disk weighs in at 6.89kg for 345x28 while retaining the parking brake. I have not settled on a front just yet (hence this thread)

Next Brake balance. Our OEM setup is too conservative with a bias of around 69.x (single pot) or 68.x (Brembo) from what I recall from the top of my head. A slightly greater rear is needed IMHO. If you recall, this motivated me to first report and mount the E38 750 vented rear on the E31 nearly 15 years ago and bring that the community. Ferrari realized this too...First realize the 550 (also front engine V12 GT) has more rear bias from factory then our cars, but was still more front biased then the 456. Ferrari realized this was an error and in the update/redesign, the 575 was tuned to yet more rear bias (around 66 if I remember correctly). Now, too much and the car is squirrely (I did fun experiments with bias valve years ago), so a critical balance must be struck. That said I want to stress, this is based purely on my opinion (well, mine and Ed Raether). This time instead of just an E38 vented rear I am designing everything ground up.

Next calipers: The brembo E31 calipers are marginal. As you know BMW cheapened out in their contract with Brembo and as a result we have issues with piston seizing and long term durability. The Euro CSI is a much better caliper at cost of weight (though not technically legal on US roads if I recall correctly). However there ARE better period correct calipers which are lighter with a wider pad selection that still retain the correct piston sizes I need to balance my rear. The Brembo/Ferrari F50 caliper which came out in 94 is a perfect example.

Next venting + ducts: Obviously vented rotors are a given, in the front in particular. (A valid argument can be made for solid rears are adequate for gentle cruisers who only ever need a single or two emergency stop and minimal endurance/sustained fade resistance. Again not my goal but I can see it valid for another person.) Ducting is important as our system is above average by mid 90s standards but here again see above goals. In a nutshell: vents are a give

Next pads: I wish BMW/Ferrari/Porsche/etc knew so they could stop wasting time for their steel brake cars and just the same Textar compound! Have you considered reaching out and letting them know? On serious note, textar made a great pad circa 1995. There has been massive improvements in both fade resistance and bite (again at cost). I am currently using Ferodo DS2500 on two of my GTs with excellent results; before that I used R4S pads (noisily if you dont bed correctly). https://pages.ferodoracing.com/produ...ke-pads/ds2500 For my E31, I am planning to use an R4S variant pad with a higher cold μ which is sustained over a wider temp range.

So to summarize, I am still working on it within the stated goals/objectives. So that means no carbons. Incidentally, I actually explored this option several years ago. It would be a rather straight forward custom job. BUT as I am sure you know, carbons brakes would be horrible with our booster system...simply too much travel for a given level of pressure. As we move to the roughly 3rd generation system now it may be better but I stopped investigating about a half a decade ago). Furthermore the brakes must fit under 18in wheels for two reasons (1) Driving with even ultra-light 19s feels like driving with lead shoes/parking brake on and (2) 19s only became readily available after the E31 was out of production. Honestly if I just wanted to go all out I would have done what I did with my E38 and use Brembo 6 piston 380mm front and 4 piston 380mm rears. That would be overkill and again fails to meet my stated objects.

Anyway thanks for the information.

CF91352C-CDF7-4757-98C3-CA3FAD90C4AA.jpeg

[Auraraptor]

The Euro E39-M5 uses a similarly dimensioned Aluminum hat semi-floating rotor except without the 18mm hub pins.
In the US that rotor is an all cast version that weighs 3lbs more.

Rod do you have this technical print out for the front 324x30mm OEM rotor (34116756087), rear 324mm OEM rotor (34216757749), and the Euro CSI 328x20 rear rotor (34216767062)?

I most am curious if the CSI 328x20 rear has a 180 or 185 parking brake hub diameter, thanks.

I ask as the OEM parking brake repair kit (34416761294) is the same between E31/E38/E52....hmmm

[m6bigdog]

Auraraptor

Rod do you have this technical print out for the front 324x30mm OEM rotor (34116756087), rear 324mm OEM rotor (34216757749), and the Euro CSI 328x20 rear rotor (34216767062)?
I most am curious if the CSI 328x20 rear has a 180 or 185 parking brake hub diameter, thanks.
I ask as the OEM parking brake repair kit (34416761294) is the same between E31/E38/E52....hmmm

The info you seek has been discussed before:
A survey of rear brake calipers -
https://www.bimmerforums.com/forum/s...t=Hyper+search
also:
Rear Brake Upgrade - More than just Vented Rotors -
https://www.bimmerforums.com/forum/s...-Vented-Rotors

The E31, E32, E34, E38 and E52 are all 180mm E-Brake shoe-drum.
The E39, E46 and later model BMW models are 185mm E-Brake shoe-drum.
I would never use a 185mm E-Brake drum rotor with a 180mm E-Brake shoe, unless you have the OE 180mm shoe re-arced to 185mm.

Rotor dimensions you requested attached:

I also included the image of the E39-M5, Euro Aluminum Hat floating rotor installed on my 850.
Mods to install in my "Rear Brake Upgrade - More then just Vented Rotors" post.
E39-M5 Euro rear rotor upgrade is more expensive than an all cast 328x20mm rotor and not a direct bolt-on, but IMHO, modifications are simple and well worth the effort when you seek a more aggressive brake bias.

IMHO this is not ART... this is simply: doing the Reverse Engineering (requires the engineering systems knowledge) and searching for parts fitment.
If you don't use math and the engineering factors how do you know how much and/or what direction you are going.

[Auraraptor]

Your knowledge and archive never ceases to amaze, thank you! I’ll save it now so I have it.

Edit: And I agree to disagree, elegant implementation of math end engineering for a particular goal is very much an art.