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Hi,
got my E32 4 piston calipersinstalled - really makes a difference! I recommend it.
Same up grade as the E31, Brembo aluminum caliper upgrade, only the Ate is a cast iron caliper with 40/44mm piston over the 324x30mm all cast iron rotor.

The Stock M5 with 315mm rotor has identical torque calculation numbers as the 4-pistion caliper with 324mm rotor because while the 324mm rotor is a little larger the 4-pistion caliper is a little smaller than the 60mm single piston stock caliper.

The Euro M5 rear 328x20mm rotor works well with the larger 324mm front rotor upgrade and adds another 1% more rear brake bias with, which I like the added anti-lift suspension dynamic.. except the rear dust shield need to be replaced and that requires pulling the rear axles and installing new bearings. You can justify the bearing because it is a PM task on these older M5's. A lot of work but well worth the effort.
 

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Discussion Starter #3
Same up grade as the E31, Brembo aluminum caliper upgrade, only the Ate is a cast iron caliper with 40/44mm piston over the 324x30mm all cast iron rotor.

yes the ate caliper is heavy, but I doubt that most people will notice this...
If you compare prices I can easily ignore this fact...
 

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Discussion Starter #4
Same up grade as the E31, Brembo aluminum caliper upgrade, only the Ate is a cast iron caliper with 40/44mm piston over the 324x30mm all cast iron rotor.

The Stock M5 with 315mm rotor has identical torque calculation numbers as the 4-pistion caliper with 324mm rotor because while the 324mm rotor is a little larger the 4-pistion caliper is a little smaller than the 60mm single piston stock caliper.

The Euro M5 rear 328x20mm rotor works well with the larger 324mm front rotor upgrade and adds another 1% more rear brake bias with, which I like the added anti-lift suspension dynamic.. except the rear dust shield need to be replaced and that requires pulling the rear axles and installing new bearings. You can justify the bearing because it is a PM task on these older M5's. A lot of work but well worth the effort.
Even if the sum of torque is identical - does not mean you have the same pedal and brake performance...
There is quite a difference between stock 315 and this brake setup.
And a bigger diameter also means more surface meaning quicker cooling times...
 

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Discussion Starter #5
Same up grade as the E31, Brembo aluminum caliper upgrade, only the Ate is a cast iron caliper with 40/44mm piston over the 324x30mm all cast iron rotor.

The Stock M5 with 315mm rotor has identical torque calculation numbers as the 4-pistion caliper with 324mm rotor because while the 324mm rotor is a little larger the 4-pistion caliper is a little smaller than the 60mm single piston stock caliper.

The Euro M5 rear 328x20mm rotor works well with the larger 324mm front rotor upgrade and adds another 1% more rear brake bias with, which I like the added anti-lift suspension dynamic.. except the rear dust shield need to be replaced and that requires pulling the rear axles and installing new bearings. You can justify the bearing because it is a PM task on these older M5's. A lot of work but well worth the effort.
I was looking for the 328 rear calipers for some time, biut they are hard to find and also quite expensive - I don't think that it is worth the effort and money...
 

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I was looking for the 328 rear calipers for some time, biut they are hard to find and also quite expensive - I don't think that it is worth the effort and money...
Interesting,
I always wonder why anyone would upgrade the thermal capacity for the front brakes and maintain the stock rears.
After all it is a brake SYSTEM, where the brake torque bias and thermal balance are interconnected.

Although to some I know little, however, I have used all the available information, data, performed measurements and calculations to evaluate anticipated brake performance. With that, the E34, M5 with a 69/31% torque bias had a an almost perfect 49/51% thermal balance and now with 324x30mm rotors in front the thermal balance will be 45.5/52.5%. Hence, of the total thermal load for the brakes the rears thermal balance has increases meaning they will be that much hotter when compared to the fronts.

A laser or contact thermometer can be used to verify the thermal balance of any brake system by just making a few hard brake applications and then quickly measuring the rotor temperatures. To get a good profile you will want to perform the brake application test and measure the rotor temps several times.

Now with the 324x30's on the front, while the brake bias was maintained and additional thermal capacity is in the front, the weak link is still the rear rotors since their thermal capacity hasn't changed (below the stock fronts) and the extra cooling capacity of the front rotors does nothing to prevent the rear rotors from fading first as they would with 315x28mm front rotors since the rear brakes still need to dissipate the same torque and thermal load.

As with any brake system it doesn't really matter which axle fades first, once you get into brake pad fading, the brake system has failed.
Philosophically speaking, if brake fade and thermal capacity is not of concern then BBK's do nothing with respect to brake performance.
 

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As with any brake system it doesn't really matter which axle fades first, once you get into brake pad fading, the brake system has failed.
Philosophically speaking, if brake fade and thermal capacity is not of concern then BBK's do nothing with respect to brake performance.
Here we go again...........

Would be nice to see some actual details of some braking results. The brakes, the circuit length, the speed braking from and how many laps were covered before the brakes started to fade?

It's all well and good stating something, but would be nice to see some facts.
 

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Here we go again...........

Would be nice to see some actual details of some braking results. The brakes, the circuit length, the speed braking from and how many laps were covered before the brakes started to fade?

It's all well and good stating something, but would be nice to see some facts.
Yes, here we go - you want to change an engineered system by guessing.
You have yet to understand facts and detail I have provided thus far.
Now you want others to do all the work for you or not question your insufficient review of your unanalyzed brake upgrade proposal.
I have done my homework and engineering analysis and I find no benefit in taking on the liability for supplying the complete details of my analysis and experience to you; specifically, so you can infer this is what I told you to do.

I have provided you with plenty of relevant detail on the proposed upgrades and if this doesn't make sense to you, you will want to take some time to study "ground vehicle brake systems dynamics" to familiarize yourself with the theory and practical design concepts, instead of spouting something about irrelevant circuit length, speed and lap until brake fade. Especially since an experienced driver can run faster laps without stressing the brake while the inexperienced driver would have used the brakes excessively to fade. So, I anticipate, your a set-of-the-pant guy that believes vehicle engineering takes a back seat to just swapping parts and tracking the vehicle!! Perception is not fact!!

So, why don't you spend a few bucks on a laser thermometer, do some braking runs and make a few rotor temp measurements for yourself instead of ragging on me for something you don't yet understand and want to know.
With all due respect,
 

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Again you avoid the questions asked........show me your setup on your e34 m5 so we can see how your system works? That is unless you don't have a set up.

There is more than one brake set up that would work sufficiently too. Assume all you like, but as you don't know me or my driving I suggest you keep your comments to yourself. how do I brake - late, very late
 

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Again you avoid the questions asked........show me your setup on your e34 m5 so we can see how your system works? That is unless you don't have a set up.

There is more than one brake set up that would work sufficiently too. Assume all you like, but as you don't know me or my driving I suggest you keep your comments to yourself. how do I brake - late, very late
Who cares about sufficient, why would you upgrade for sufficient?
That is what the engineering analysis is all about, so you upgrade to optimal!!!

So, here is a setup for you.
Guess what it is and just maybe I'll show you more!!
Hint, it is not a BMW factory option...
Just don't ask how to do it.
 

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I thought the forum was meant for information sharing
and not for information do not give
Exactly,
Read my reply's and original posts!!
I supply an abundance of technical data, detailed prospective and opinion on the subject posted from my experience and engineering mathematical analysis.

I answer each query with additional summary analysis and relevant data. There is a ton of engineering mathematical analysis behind the balance/increase in performance data and percentages I post and if I was to post all the analyzes data, graphs and spreadsheets the opportunity for the casual reader to extract the relevant summary from the complex raw data is slim to none. Let alone the file sizes exceed and upload limits for the forum file types.
OMHO, track testing is unrealistic as proof of concept and/or factual analysis as the uncontrolled variables of driver skill, roadway surface and tire compound all can overwhelm/cloud the opportunity to analyze the actual upgrade in performance. So why attempt to make it the focus of the general systems analysis.

Also, it is unrealistic to expect me to write an online technical training manual or explain the engineering factors and theory online if someone has yet to sufficiently explore the available How-To books and/or engineering theory text that are the foundation of the very technical/engineering subject the want to discuss in their OP or in reply to my comments.
The "Fundamentals of Ground Vehicle Dynamics" is far to complex a mechanical engineering subject to argue the system dynamic fundamentals and mathematical analysis on a text forum with someone that just wants to argue for argument sake; with little to contribute and/or relevant technical training and knowledge.

I am not typically so condescending. However, IMHO - some individuals that get in over their head and don't want to be criticized for a poorly thought out proposal will work very hard to dis any and all that is posted in reply, with subjective and/or irrelevant "well buts" to bring the exchange down to their other than technical level.
Sorry to disappoint, I'm not going there!
 

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Discussion Starter #13
really? i wonder why quite a few racing people i know ride exactly this setup. Your whole statement seems to be very very theoretical.

1: I doubt that most e34 m5 drivers ever reach fading in normal street mode.
2: even being located in germany and really being able to reach top speed - I never had fading issues in street driving.
2: why do you give % when your sum is not 100?
3: even if your calculation is right - 1,5% difference - really? so tell me -what is this is °C?
4: I had fading in other cars before - and I'd rather have fading on the rear brakes that on my front brakes.
5: my idea was never to have a race / fading optimised brake system - then I would rather take something like ap brakes.
I only wanted a brake that works a bit better without spending 3000 € or more. And it does! everything else is blablabla.
dont take it personal. i dont mean to offend anyone here.

Interesting,
I always wonder why anyone would upgrade the thermal capacity for the front brakes and maintain the stock rears.
After all it is a brake SYSTEM, where the brake torque bias and thermal balance are interconnected.

Although to some I know little, however, I have used all the available information, data, performed measurements and calculations to evaluate anticipated brake performance. With that, the E34, M5 with a 69/31% torque bias had a an almost perfect 49/51% thermal balance and now with 324x30mm rotors in front the thermal balance will be 45.5/52.5%. Hence, of the total thermal load for the brakes the rears thermal balance has increases meaning they will be that much hotter when compared to the fronts.

A laser or contact thermometer can be used to verify the thermal balance of any brake system by just making a few hard brake applications and then quickly measuring the rotor temperatures. To get a good profile you will want to perform the brake application test and measure the rotor temps several times.

Now with the 324x30's on the front, while the brake bias was maintained and additional thermal capacity is in the front, the weak link is still the rear rotors since their thermal capacity hasn't changed (below the stock fronts) and the extra cooling capacity of the front rotors does nothing to prevent the rear rotors from fading first as they would with 315x28mm front rotors since the rear brakes still need to dissipate the same torque and thermal load.

As with any brake system it doesn't really matter which axle fades first, once you get into brake pad fading, the brake system has failed.
Philosophically speaking, if brake fade and thermal capacity is not of concern then BBK's do nothing with respect to brake performance.
 

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M6BD,

Some interesting points there.
Was there any change in the rest of the braking system when the M5 brake setup was changed from the original 315x28/300x10 to 315x28/300x20 setup? And what change would that make to your calculations?
Also what would the differences in effectiveness be to the E32 which uses 328x30/300x20 ?

I'm not trying to wade into either side of any argument here, just curious. With my car I upgraded all 4 corners from the original M5 to the E32 setup.
 

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really? i wonder why quite a few racing people i know ride exactly this setup. Your whole statement seems to be very very theoretical.

1: I doubt that most e34 m5 drivers ever reach fading in normal street mode.
2: even being located in germany and really being able to reach top speed - I never had fading issues in street driving.
2: why do you give % when your sum is not 100?
3: even if your calculation is right - 1,5% difference - really? so tell me -what is this is °C?
4: I had fading in other cars before - and I'd rather have fading on the rear brakes that on my front brakes.
5: my idea was never to have a race / fading optimised brake system - then I would rather take something like ap brakes.
I only wanted a brake that works a bit better without spending 3000 € or more. And it does! everything else is blablabla.
dont take it personal. i dont mean to offend anyone here.
Professional & serious racers have an engineer behind almost all the suspension and brake system changes.. So, yes it is all very theoretical, mathematical and that is what it take to analyze the system dynamics.
Do you assume the ///M guys just showed up at a race track with an 535i and bunch of parts to start the M5 project? Or do they crunch the numbers and analyze the dynamics to balance of the proposed performance upgrades; typically driven by the engine package? I don't think you will find a single non-engineering racer on the BMW vehicle engineering design team. Racers may test the changes but to understand the full impact and dynamics of the proposed performance changes it take more than just knowing when to turn the wheels and press on the brakes...

So I do some theoretical analysis and to you think it is poison!!

1) normal street mode? I don't drive an M5 for normal street mode! I drive it to take driving to the next level.. take some risks I would not take with a lesser vehicle. I also tune my M5 so it will be all it can be and the additional performance margin supports the risks caused by speed. Remember Speed Kills - That is a good statement with a Yugo but not so much when you have the performance margin engineered into the M5.

2) a single stop from 120MPH will put the stock brakes very near if not into the fade temperatures curve and spirited driving and/or carrying speed on twisty mountain roads and you can easily be there.

3) obvious to me that is a typo! correction: 45.5/54.5% = 100% and it is uses to show the trend of greater imbalance and a place for improvement. I anticipate that is what the 750 brake upgrade was intended to be? an improvement without taking it to the top?

4) the % is 3.5% and the °C rise is a matter of how much brake application is involved, that is driving around town and who cares what brakes are on the M5 however from 120-0 MPH would put the 300x20mm rotors near 650°F. not good for the rotor. That temp would certainly increase the stopping distance. IMHO, So why does a vehicle have brakes? To avoiding collisions. A collision is typically all a matter of inches and after the collision it is too late to upgrade the brakes to avoid the collision.

5) This I want I'm getting at, So why change to 324x30mm rotor and 4 piston caliper as the bias is almost identical to the stock M5 brakes and with the stock rear brakes as they will fade first just like they would with the stock 315x28mm front rotors so while you didn't spend 3000 € on the upgrade your money didn't buy much in the final theoretical analysis and if you don't use the stock brakes to their limit the upgrade didn't provide an additional margin anyway irrespective if the analysis; theoretical or track tested.
 

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M6BD,

Some interesting points there.
Was there any change in the rest of the braking system when the M5 brake setup was changed from the original 315x28/300x10 to 315x28/300x20 setup? And what change would that make to your calculations?
Also what would the differences in effectiveness be to the E32 which uses 328x30/300x20 ?

I'm not trying to wade into either side of any argument here, just curious. With my car I upgraded all 4 corners from the original M5 to the E32 setup.
Until your reply, I was unaware the early (up to 10/89) M5 had a 300x10mm rear rotor.
The source I use for the caliper piston size to calculate the brake torque does not show that early 300x10mm rear brake M5 setup. It is certainly in RealOEM but I need the specifications.

The E34, 535i has a 300x10mm rotor with a 38mm caliper piston but the M5 didn't use that caliper so I anticipate the M5 used the upgraded 40mm (edit: I did some research and the early M5 with 300x10 rotor did use the 535 caliper with a 38mm piston so the bias is not the same as the M5 with 300x20mm rotor) piston with the 300x10mm rotor to correct the balance for the 315x28mm rotor with 60mm caliper piston. The other 5's with the 300x10mm rear rotor also uses a 302x22mm front rotor which is telling you something about the thermal capability of the 300x10mm rotor.
Using a 300x10mm non-vented rotor is huge mistake on the M5, not with the brake torque bias/balance but with the thermal balance as the rears will get super hot and fade and then the front brakes must carry the rear brake duties (30% increase) and that will cause the fronts to go into fade in short order. I anticipate the ///M guys saw that mistake and made the change to 300x20mm rotor early in production. The E32, 750 always used the vented 300x20mm rotor. In fact if you look at the specification of the later model M5's (E39, E60, etc.) the increase of rear brake bias, increase in rotor size, caliper piston size compared to the front caliper and rotor size is a recognition that the rear brakes can play a significant role in balancing the heat generated by the increasing brake torque for increasing brake performance. However, to utilize the shift to more rear brake bias a dynamic brake bias controller is uses so the rear bias is shifted to the necessary 70/30% bias during the hardest brake applications because weight transfer dictates that shift to match the reality of the tire traction models from the weight transfer, i.e., in reality tires stop the car and for optimal brake performance all 4 tires must be used to their full potential.

I had a new 88M6, owned it for 15 years, and the first real performance issue that was discussed was warping of the front rotors!!
The brakes were front 300x30mm with 4-piston (40/40mm) caliper and 284x10mm rear rotor w/36mm rear piston caliper.
I did some brake torque and thermal (t-rise) calculation and it was obvious to me when the front rotors were warping it was all do to the small rear brake setup fading (same as the 635/735 rear brakes). So while many with the M5/M6's were changing out the front rotors and/or upgrading the front brakes to solve front rotor warping, I spent much less and changed the rears and uses the E34, M5 rear 300x20mm rotor and caliper w/40mm piston setup. I posted my finding and many others started rear brake upgrade as the solution to front rotor warping in the early 1991-92's. After the rear brake upgrade, the E24, M6 brakes had a better bias and thermal balance and the overall brake and chassis performance was much improved with much less rear end lift during hard braking and I never warped a front 300x30mm rotor as the brakes had a good thermal balance that allowed you to drive the M6 much harder and not get any of the rotor hot enough to make them fade.

In a simple analysis the rotor width and venting/or not tells you the thermal capability and the caliper piston size indicates the brake torque capability and bias. That is the 300x10 has less thermal capability than the 300x20mm rotor however the brake torque and bias would be identical if the caliper piston is the same size. You can also mix and match a larger rotor as is done with the 324x30mm and use the 4-piston caliper and end up with the same brake torque and bias as the 315x28mm rotor with the single piston 60mm caliper however the thermal capability of the larger 324x30mm rotor can be realize but only if the rear brakes are sized so they won't fade before the more capable larger front rotors can come into play.

So lets look at the 750 with the 324x30mm rotor with the 4-pistion (40/44mm) front caliper and 300x20mm rear rotor setup.
One could say WOW, I could upgrade my M5 to the 324x30mm front brakes because I have a 300x20mm rear rotor and I would have the same brake bias and thermal balance on my M5 brakes as the 750. But you'd be mistaken, because the 750 used a 38mm rear caliper piston while the M5 uses a 40mm rear caliper piston. Therefore, the brake bias for the M5 provides more rear brake torque that puts more thermal load on the 300x20mm rotor than the 750 setup with the same size rear rotors!! I have yet to do the bias and thermal analysis calculations of that 750 brake setup.
Yep, a not so obvious 750 brake upgrade with an rotor thermal imbalance when installed on the M5. Hence, why I suggest with support of the engineering analysis of the M5 rear brakes that the 750, 324x30mm rotor upgrade also needs the 328x20mm rotor to balance the thermal improvement of the bigger 324x30mm front rotors. That upgrade can be done with the late M5 328x20mm rotor and a E38, 750 caliper that also uses the 40mm piston with a 328x20mm rotor. The caliper flex line threads in a little differently location but to my knowledge it is workable solution on the E34.

I hope that answers you questions.
 

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All these brake calculation threads, major lol!

I've put a set of AP front brakes on 3 of my last 4 performance cars, an Impreza, an r33 Gtr and an e39 m5. Same caliper, slightly different disk sizes, no rear upgrade other than pads. No maths!

In all cases the brake pedal feel, the braking performance over multiple stops (pedal feel, pedal travel, retardation consistency) and hence confidence in the braking SYSTEM has improved dramatically over the stock brakes. I didn't upgrade my e34 m5 because I could not justify the cost of the AP kit vs what I paid for the car......
 

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All these brake calculation threads, major lol!

I've put a set of AP front brakes on 3 of my last 4 performance cars, an Impreza, an r33 Gtr and an e39 m5. Same caliper, slightly different disk sizes, no rear upgrade other than pads. No maths!

In all cases the brake pedal feel, the braking performance over multiple stops (pedal feel, pedal travel, retardation consistency) and hence confidence in the braking SYSTEM has improved dramatically over the stock brakes. I didn't upgrade my e34 m5 because I could not justify the cost of the AP kit vs what I paid for the car......

Look Ma.. No Math!!
Just goes to show you, even a blind squirrel can find a nut every once and a while.
Aren't you glad the brake engineers at AP did a good job of sizing the calipers for you!!
Sorry, I bet you thought you did it all on your own.
And just think, you'll never know how good it could have been with a rear brake upgrade.

LOL, You should hope you never buy a car that is built the way you modify yours!!... bolts on good nough...
Saves on all the head scratching..
Give me a break..
 

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Why not just find a 345/328 set from a parts-out M5?
And how does that factory setup (unchanged even for E39 M5, afaik) compare to aftermarket setups of similar size?
 
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