Why does BMW not use Brembo brakes

[attila]

Originally Posted by FStop7

How many of you have even faded the stock brakes, anyway?

It is not difficult to experience some brake fade on a track with stock pads. Overheating is the major issue with the stock setup.
Very likely a high end Brembo or Stoptech kit is somewhat better than stock in terms of feel or maybe even fade but without cooling they will have more or less the same problems than stock.

[rouxeny]

I think BMW is right in not putting on better brakes. The sad facts are that the vast majority, I'd say well over 95%, of owners of M3's will never put their cars on the track. Even if you look at this forum, which is comprised of some pretty die hard fans, the track subforum never has any posts!

Most M3's are for simple daily driving, and in that situation, the added cost of a "better" braking system will never be justified. The stopping distances between the current brakes and anything by Brembo are close enough to not be statistically significant. The only gain would be the fade-resistance that Brembo's may have. However, when does an ordinary daily driver manage to fade the brakes? At most, you make one crash stop, but never two or more in a row.

Why raise the cost for everybody for the gain of just a nominal few? For Ferrari's and true exotica, it makes more sense, as people are all willing to pay for such things to be standard.

[M3_WC]

Screw Brembo.

Performance Friction FTW

Those big Brembo setups are for pistion-counters, not true track junkies.

[BMW269]

I agree that most of M3 owners do not track the car, that maintenance will cost much for BMW, but why isn't it the case for Audi and Porsche? Do you think Audi RS with 4WD are more tracked than M? And about Porsche, I live near Germany an see Porsches everywhere, an even more in Stuttgart, and do you think they are tracked? And what for does Audi put Ceramic brakes on the A8 W12 or S8? I do believe that all the cars exept Ferrari, Maserati an Lamborghini get the downwatered versions of Brembo brakes, but it is quite important for looks, an RS4 looks really good with the RS4 badge on the calipers compared to an M3. And BMW does have a bad brake reputation. So in my opinion BMW does not need to put any expensive brakes, but just needs to put some pretty painted 6 piston fixed calipers with a big BMW writing or M logo as the 135i and BMW Performance brakes, and everyone shall say BMW makes good brakes. They can also ut cheap ceramic disks and they will say BMW makes the same goog brakes as Porsche. It is not so much the brke perfomrance that matters but the looks, as anyway very few track their cars.

[attila]

The stock brakes are not bad. I doubt the Brembos will have better fade resistance with the same cooling, unless you put on some very heavy rotors. The heat dissipation and capacity is the issue. You want to generate less heat (slow, lighter car) loose heat faster (cooling) or have larger capacity to "store the thermal energy" to experience later or no fade. Number of pistons, brake geometry etc has no real play in that, but maybe important in brake feel etc.

[x838nwy]

Originally Posted by attila

The stock brakes are not bad. I doubt the Brembos will have better fade resistance with the same cooling, unless you put on some very heavy rotors. The heat dissipation and capacity is the issue. You want to generate less heat (slow, lighter car) loose heat faster (cooling) or have larger capacity to "store the thermal energy" to experience later or no fade. Number of pistons, brake geometry etc has no real play in that, but maybe important in brake feel etc.

It's hard to say whether Brembos or any bbk actually has better cooling than the stock items. The amount total energy generated will be the same (same car mass and deceleration) but if the rotor offers better cooling through better design such as internal vanes or even a caliper that allows for better cooling then the temperature rise of the brake system will be less so at the end of the same braking event, the temp of a "better" system will be lower even when the thermal masses may be similar between the two.

I'm not saying it will be since I have no evidence of this, but it is possible.

The "feel" of the brakes I think has more to do with rotor/pad materials and caliper rigidity than the actual size of the components.

Finally, I think somewhere on here there's a table of weights of various systems. Some kits are lighter than stock and while the whole thermal capacity thing may be important, having a lighter brake system on the car means a reduced unsprung mass which should improve handling in the same way that having a lighter wheel/tyre combination does.

What I'm saying is that it is _possible_ that a bbk offers a genuine advantage. But said advantage may be more marginal than looks suggest. The oem system is, despite the looks of the thing, adequately engineered. If one is looking to improve their braking 'performance' then perhaps one should start with trying different pad compounds on the stock system before going for an expensive kit. A lot of the time, people confuse braking performance with brake feel. Changing pad compounds have a bigger effect than many might believe...

[lucid]

Originally Posted by x838nwy

It's hard to say whether Brembos or any bbk actually has better cooling than the stock items. The amount total energy generated will be the same (same car mass and deceleration) but if the rotor offers better cooling through better design such as internal vanes or even a caliper that allows for better cooling then the temperature rise of the brake system will be less so at the end of the same braking event, the temp of a "better" system will be lower even when the thermal masses may be similar between the two.

I'm not saying it will be since I have no evidence of this, but it is possible.

The "feel" of the brakes I think has more to do with rotor/pad materials and caliper rigidity than the actual size of the components.

Finally, I think somewhere on here there's a table of weights of various systems. Some kits are lighter than stock and while the whole thermal capacity thing may be important, having a lighter brake system on the car means a reduced unsprung mass which should improve handling in the same way that having a lighter wheel/tyre combination does.

What I'm saying is that it is _possible_ that a bbk offers a genuine advantage. But said advantage may be more marginal than looks suggest. The oem system is, despite the looks of the thing, adequately engineered. If one is looking to improve their braking 'performance' then perhaps one should start with trying different pad compounds on the stock system before going for an expensive kit. A lot of the time, people confuse braking performance with brake feel. Changing pad compounds have a bigger effect than many might believe...

I maintain the weight savings thread, and yes it has brake system weights of the stock and some aftermarket systems. However, it doesn't have the rotor weights. The closest we got was the rotor + hat weight. Given the stock rotors have Al hats--as do the aftermarket rotors--that might not be such bad basis for comparison. Based on those data, I don't get the sense aftermarket systems offer significantly more thermal mass. Who wants more unsprung mass anyway.

As I've said earlier the stock system is excellent on the track as long as it does not overheat. It just needs cooling ducts, Castrol fluid, and SS lines (and of course high temp pads).

Vane and rotor geometry also affect cooling rates, and aftermarket rotors most likely have better designs. The stock system seems to be optimized to keep manufacturing costs down.

[AP Racing - Chris_B]

Originally Posted by lucid

Vein and rotor geometry also affect cooling rates, and aftermarket rotors most likely have better designs. The stock system seems to be optimized to keep manufacturing costs down.

This is exactly why a 36mm wide disc with 42 curved vanes was chosen up front on the strap drive system. The plate thickness does not need to be a lot greater, but the air gap is larger and provides more internal airflow. Heat rejection rates are substantially better using a wider disc with better air flow, sometimes reducing bulk temperatures by as much as 150°C (302°F) when being used very hard. This is exactly how the discs on a NASCAR stocker/taxicab are kept from exploding when surface temperatures exceed 2000°F. Of course, those are 42mm wide (or more) and have 70 vanes! Note: Those brake systems cost over $30k and don't come with pads, lines or fluid -- just calipers and rotor assemblies.

The E9x M3 front disc is not in the same category as a proper aftermarket upgrade at all, even though it is technically a two-piece design (but not floating). If it were, the cost would exceed what BMW has set for a a brake budget. This is just one of the main reasons why upgrades cost more. That and the fact they are made in lower quantities, reducing the economies of scale.

There are many more differences in a correctly designed, engineered and manufactured BBK. Some of which are very small and came with decades of experience. When all added together, they make for a much better track experience than just pads, lines and fluid can possibly do. I'm not saying that people can't track the car without a huge upgrade -- of course they can, and even with good results. But the experience will definitely be different with a superior brake system.

Chris

[swamp2]

Originally Posted by AP Racing - Chris_B

Heat rejection rates are substantially better using a wider disc with better air flow, sometimes reducing bulk temperatures by as much as 150°C (302°F) when being used very hard.

You'll have to speak more precisely with well understood physical concepts than "heat rejection rates". It sounds like you simply mean improved cooling rates through convection. The physics of "rejection" or insulation is entirely different than dissipation. Recall you are often talking to a bunch of engineers here. Well maybe not a bunch but more than a few!

[AP Racing - Chris_B]

Originally Posted by swamp2

You'll have to speak more precisely with well understood physical concepts than "heat rejection rates". It sounds like you simply mean improved cooling rates through convection. The physics of "rejection" or insulation is entirely different than dissipation. Recall you are often talking to a bunch of engineers here. Well maybe not a bunch but more than a few!

My apologies, class! Seriously, I get far more grief from leaving too detailed of a response than not enough. I am getting better at boring fewer people with mundane (even if important) details, especially those that are not within the control of the end user/driver!

Of course I was referring convective heat transfer, so thanks for the correction. Well, at least primarily. At higher temperatures, conductive and radiant heat transfer also play important secondary roles. Generally speaking, more and better air flow between the disc plates leads to better cooling and lower bulk temperatures (all else being equal). The core design of the disc is a major player in that formula, but there are obviously other factors such as plate thickness, face design and drill/slot pattern and density, heat dams, cooling ducts and so on. Also to be considered is that the air flow into the eye of the disc is a turbulent mess that is far from laminar. This is why attempts at making airfoil-shaped vanes is essentially a marketing exercise with no real results away from a controlled brake dyno environment without a spinning tire/wheel assembly (among other factors) mucking things up. But I digress...

The topic of the insulation properties of different types of pad compounds, back plates, shims, piston materials/coatings, piston design, seal location, etc., is yet another discussion that gets rather dry and boring for most people right from the get-go. I'll pass on that for this thread.

My comments here are intended to highlight that there are many differences and improvements in a BBK, not just the fact the disc is larger or there are more pistons. It's a lot more complicated than that. Actually, developing a brake system for a dedicated race car is much more straightforward as there is little concern about dust, squeaks/noise, harshness, cold performance, wear rates, road salt, poor maintenance, installation challenges, ineffective air flow, etc. Producing a system that works acceptably on the street and can also handle track duty is a tall order by comparison. Offering such a system on an M3 from the factory will add substantial cost which BMW has chosen to pass on.

Of course, all disclaimers apply, your mileage may vary, I'm not responsible for your accident, yada, yada, yada.

[lucid]

Originally Posted by AP Racing - Chris_B

There are many more differences in a correctly designed, engineered and manufactured BBK. Some of which are very small and came with decades of experience. When all added together, they make for a much better track experience than just pads, lines and fluid can possibly do. I'm not saying that people can't track the car without a huge upgrade -- of course they can, and even with good results. But the experience will definitely be different with a superior brake system.

I have no doubt that a well designed BBK will offer a better experience than the stock system. That said, I maintain that people can track the car without a huge upgrade with excellent results--barring the overheating issue, which is real, but will soon be solved by ducting and backing plates.

I appreciate the nuances of designing a state of the art brake system, and the associated engineering effort. However, my main point is rather straight forward. If someone needs to ask about what those differences might be, it is likely that he/she will not be in a position to really benefit from the improvements--at least from a performance perspective. Meaning, one can explain how a well designed BBK will provide better brake modulation, but if the person does not really understand why that is important and is utilized, it is pretty much a meaningless upgrade. In other words, if the person asks a targeted question such as, "Will this system give me better brake modulation?", he/she will most likely benefit from it, but if the person asks, "What does this system do?", the potential benefits are questionable in my mind.

That is the case with pretty much every sport that is highly equipment-centric. My 2 cents...

Originally Posted by AP Racing - Chris_B

This is exactly how the discs on a NASCAR stocker/taxicab are kept from exploding when surface temperatures exceed 2000°F. Of course, those are 42mm wide (or more) and have 70 vanes!

Out of curiosity, what type of transient (during a few second braking event) temperature gradients can be observed in the example you provide above? Meaning, when surface temps are at 2000F, how much lower might the temps be at the cooling/vane surfaces? Thanks.

[rzm3]

Honestly, if BMW just made the calipers in a conspicuous color with M logos on them, 99% of owners won't even think about BBKs. A lot of people upgrade to BBKs just for the aesthetics, which is completely understandable. But technically speaking, if you only drive on the streets, you DON'T need a BBK.

I also completely agree with Lucid that upgraded lines, fluids, and pads are more than adequate for most trackers.

Anyway, some good info here. I am sure BMW monitors this forum and knows that there may be a demand for an upgrade option for the future (certainly not ceramics though). Or at least make the brakes look better. I can bet that the next gen M3 will have much prettier, and seemingly more capable brakes.

[Eugene-TAIWAN]

I think the main reason is because that our cars are so balanced compared to other cars! Most cars are still heavy on the front end of the cars. Especially Audi's

[x838nwy]

Originally Posted by lucid

However, my main point is rather straight forward. If someone needs to ask about what those differences might be, it is likely that he/she will not be in a position to really benefit from the improvements--at least from a performance perspective. Meaning, one can explain how a well designed BBK will provide better brake modulation, but if the person does not really understand why that is important and is utilized, it is pretty much a meaningless upgrade.

Totally agree with you there. The thing is, the brake system is not something as simple as a power upgrade. With that you get some tune, filter, pulleys and an exhaust and the gains are measurable on the dyno. With brakes, things are different. You can measure stopping distances and so on, but it's debatable how much relevance that has on track times or normal use.

At the end of the day, I think it's appropriate that vendors offer buyers information and a choice. There are ways to improve on the stock system without going all out. I rather like what StopTech does by offering a package with, IIRC, rotors, pads, fluid and lines as a sort of stage 1 then a bbk as a stage 2. I'm not saying what AP, Brembo, PF, etc. are offering is wrong. They all make excellent products, I'm just saying that the general modding public should be made aware that while component upgrades may not offer the ultimate in deceleration and modulation thereof, it is for a lot of cases an adequate solution.

Having said that, my M3 will get the AP system front and rear some day. And no, I don't track the car. I'm getting it for looks

p.s. I've always been a fan of AP products. Had their system on the cars I raced a long time ago and not a single problem. Always dream of having the system on my car but they never seem to make a kit for the car I actually own!

[swamp2]

Originally Posted by AP Racing - Chris_B

My apologies, class! Seriously, I get far more grief from leaving too detailed of a response than not enough. I am getting better at boring fewer people with mundane (even if important) details, especially those that are not within the control of the end user/driver!

Thanks Chris, good reply. Especially the part about how difficult it is designing for a street car that will see track use. Having done some brake design/research/testing myself I can appreciate all of the details. I did a lot of development of the first cable actuated full hydraulic mountain bike disc brake system for which I had full responsibility for design, development and testing of the ceramic brake pistons.

Despite all of the subtle nuances of a highly engineered system you also can't lose sight of the basics. Pads are more important than rotors and in rotor design the rotors mass, and specifically the mass of the iron portion (or CSiC portion in a composite rotor) of the rotor is the most important factor (all else equal or within normal ranges of real designs).

[lucid]

Originally Posted by x838nwy

Having said that, my M3 will get the AP system front and rear some day. And no, I don't track the car. I'm getting it for looks

IMO, if one indeed fully appreciates the engineering effort behind a well designed system and desires to own a fine piece of machinery, that is grounds for purchasing it even if one might actually never be able to really benefit from it from a performance perspective (even if it just secretly sits in your garage). I think there is often too much scrutiny against people who make such purchasing decisions. What I personally do not get is people purchasing such pieces of fine machinery without having any significant appreciation for what they are buying, and buying just because it is trendy, "cool", or something like that. [Flame suit on]

[x838nwy]

Originally Posted by lucid

IMO, if one indeed fully appreciates the engineering effort behind a well designed system and desires to own a fine piece of machinery, that is grounds for purchasing it even if one might actually never be able to really benefit from it from a performance perspective (even if it just secretly sits in your garage). I think there is often too much scrutiny against people who make such purchasing decisions. What I personally do not get is people purchasing such pieces of fine machinery without having any significant appreciation for what they are buying, and buying just because it is trendy, "cool", or something like that. [Flame suit on]

Appreciate your understanding, dude. It's refreshing not getting flamed or having to 'prove' that I 'need' it to buy it

The last bit of what you said I totally hate and it's sadly these "all gear no idea" folks who go around talking $hit about a product that's actually of quality just 'cos they can't use it properly or don't know what it's about. The number of people (on some other forum, not so much this, happily) complaining their tis off about race pads being loud and dusty is a case in point.

[euro]

Originally Posted by FStop7

How many of you have even faded the stock brakes, anyway?

--- raises hand

Summit Point Main, stock pads and fluid

I dont want anything to do with a BBK, I just need pads and some cooling ducts.

[AP Racing - Chris_B]

Originally Posted by lucid

Out of curiosity, what type of transient (during a few second braking event) temperature gradients can be observed in the example you provide above? Meaning, when surface temps are at 2000F, how much lower might the temps be at the cooling/vane surfaces? Thanks.

While I'm not on the road with NASCAR boys these days (frequent flier miles just aren't as sexy to me as they used to be!), bulk temperatures -- measured at the core of the rotor -- can be anywhere from 400-600°F lower than surface temps at any given moment. Of course, this is a dynamic situation that is highly dependent on a lot of factors. At 2000°F, surface temps drop quickly as well.

We just tested the first set of (aftermarket) carbon-ceramic rotors on a Targa-prepped Nissan GT-R this morning and saw enough surface temperature during bed-in to cause the rotors to glow -- in bright daylight! But the bulk temperatures were substantially lower.

Chris

[AP Racing - Chris_B]

Originally Posted by lucid

What I personally do not get is people purchasing such pieces of fine machinery without having any significant appreciation for what they are buying, and buying just because it is trendy, "cool", or something like that.

I don't necessarily 'get it' either, but the more product people buy, the lower prices can be brought down for people who do have a significant appreciation. If only a few people invested in quality brake upgrades every year, the serious track guy would have to pay a lot more than he would today. Or, the manufacturers would just quit making them due to lack of sales.

[JC919]

B/c they're independent!

[lucid]

Originally Posted by AP Racing - Chris_B

While I'm not on the road with NASCAR boys these days (frequent flier miles just aren't as sexy to me as they used to be!), bulk temperatures -- measured at the core of the rotor -- can be anywhere from 400-600°F lower than surface temps at any given moment. Of course, this is a dynamic situation that is highly dependent on a lot of factors. At 2000°F, surface temps drop quickly as well.

Interesting. I understand there is no single simple answer. I just wanted to get a sense of potential variations. Thanks for the info.