E28 535is versus M5 Brake Systems

E28 technical advice asked and given! Troubleshooting, modifications and more.
gusgriff
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E28 535is versus M5 Brake Systems

Post by gusgriff »

I hear from all the post an opinion that the brakes are better on the E28 M5 rather than the 535is version. Knowing the M5 is a better performance car. I beleive this in most areas but I could not with the brakes with the data I can gleen from engineering data I had found so far. The E32 735i and E34 540i brakes are to be considered and mentioned in the my future plans. The research done and shown below is not meant argue with anyone who has done these upgrades or to change anyones opinion that is considering these upgrades. This is done for my benefit, to understand the engineering and do a cost benefit study. I am asking for the forum's members to look an my reseach and correct any errors and add any clarifications.

This is what I have found which is missing specific engineering data and the questions that arise due to this.


Master Cylinder ( Hydraulic Power Generation) ===========

What is the difference between the E28 535is and M5 Master Cylinder What is the output pressure and volume differences?

E28 535is Master Cylinder #34311153053 is different PN from E28 M5 Master Cylinder #34311155270 but same size and type: 23,81MM ATE

The Brake Servo and Pressure Regulator are the same.

Do not know brake pedal moment arm differences and how this effects Master Cylinder input pressure.

Do not know differences in timed flow in cubic centimeter per second or response delay but cannot be significant.

The front and rear brake bias is not significantly different between the two cars.


Rotors ============

Front Rotors are 18mm larger in diameter and 5mm thicker which does improve the heat abatement characteristics thus reducing fade. The larger diameter can improve the brake moment arm but I have no data on the delta distance centerline of wheel relative to centerline of braking force from pistons/pads. If greater distance it may be offset by the increased inertial mass due to the rotors and the added vehicle weight.

Rear Rotors are the same.


Brake Calipers =======================

Saw some info on the forum that can lead one to believe that the 535is have only 1 piston per front caliper and the M5 has 4. The M5 does have 4 pistons but 2 per wheel caliper and the 535is has 2 pistons or 1 per wheel caliper. The piston bore or pressure area of both are virually identical. 535is has a 57mm bore (2550 sq.mm) and the M5 has two 40mm bore pistons (2512 sq.mm)

The front calipers are #:34111160369/370 for the 535is and the calipers repair kit is #34111153208, (ATE FN-57)

The front calipers are #:34112225002/003 for the M5 and the calipers repair kit is #34111158692 front and rear

Rear calipers are different #34211160397/398 and #34211160393/394. The piston bore is the same as both use the same piston repair kit #34211153194.
NOTE: Though number are the difference the carriers are the same so maybe BMW gave the calipers a different number so they could charge more since it would go on a more expensive car.


Brake Lines ==================================

Higher pressure and flow volume at the caliper input port will signicantly change the piston force to the pads negating the fact that the overall piston area is the same. As asked above what are the pressure and flow volume differences between the two systems. The diameter of the brake lines supplying the caliper input ports is identical. If the M5 has a higher flow volume why would be brake line be the same because with increased flow the pressure drop increases. Higher input pressure would be needed to overcome the increase pressure drop but this does not seem the best approach.


Brakes Pads =================================

Jurid pads are OEM for both cars but with different compounds. The M5 pads do appear larger by 10-20% and this will increase the fictional drag thus improving stopping power. I question how much if the the hydraulic power supplied by both the 535is and M5 brake systems is the same. The larger M5 pads would be lesser pressure per square mm but the overall force should be the same.
The formula for frictional stopping power is (Force due to friction = coefficient of friction x Force due to pressure). Assuming the compression force is the same this is not the answer


The 535is uses JURID 508 #34211157925 and the M5 uses ENERGIT 582 #34212226013 which is also a Jurid and both look identical.

Do not yet know the difference in the pad compounds. The coefficient of friction may be better on the M5 type and they may have better heat abatement thus resist fade better. The pads with the three gaps between sections does enhance the heat abatement. The main purpose of the pads and rotors outside of stopping the car is this Heat Abatement. With the facts above the larger pads even creating less PSI force on the rotors coupled with the pads four sections and a better compound must abate/dissippate the heat generated more efficiently.



CONCLUSION =========================================

I still believe the M5 brakes are better but not that much significantly better, maybe 20%. I believe this improvement is due solely to the front brakes. I could not justify spend the money for front and rear M5 calipers to upgrade my 535is. Even if I raced this car the most I would do is the fronts with the M5 types. The next step would be to upgrade the rears with the e32/e34 types. I did this exercise to justify in my mind if the engineering backed up the desire for the "wizbang gotta have one of those" trap that we motorheads tend to jump into headfirst. If I were a rich man or had no other financial responsiblities, I to would want the best and what the hell if the improvement does not justify the cost.

As stated several times above some enginnering was not found and assumptions were made as to the significance of said missing data. I am stubborn and anal and maybe to some a little flawed in my approach. If you have solid engineering data to pass on, I would greatly appreciate the education even if it proves me wrong. I promise to admit it in this forum.

Some of you will disagree and think me an a..hole and a fool. Some of you will argue with me and state this on this forum. Some of you that do this without solid engineering to back your opinion up will do so because of your own agenda. I welcome all data and opinions and my agenda is only knowing the facts.

CREDITS: My data was gleened from a similar study found on this forum, RealOEM.com, online vendors and manufacturer websites.


NEXT STEP =============================

I will do this same exercise for the E32 and E34 brake systems. My preliminary opinion based on the reseach does thus far is guarded. The e32 735i & e34 540i front brakes are the same and an improvement over the e28 535is fronts but may be equal with the e28 M5 brakes. Though the e32 735i rear brakes are a slight improvement over the e28 535is rear brakes, the e34 540i rear brake appear to be a much greater improvement. The e34 540i brakes should be an improvement but the e28 535is may not have the hydraulic Power of the e34 540i. The brake lines are smaller on the 535is so voumeric flow and pressure would not be the same. I have yet to determine the Master Cylinder, Brake Servo and Pressure Regualtor differences. I hope this is more positive.
I am still a "Motorhead and have to fight the attitude of "I gotta have one of these".
Rich Euro M5
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Post by Rich Euro M5 »

Your information regarding the E28 M5 front brake calipers is incorrect. They have 4 pistons / caliper. If you used Real OEM to draw this conclusion, it's due to you misinterpreting the parts breakdown and the number of rebuild kits needed.

The rear brake calipers on the Euro E28M5 have slightly larger pistons than the standard calipers used on the 535i, but not so much more that I would consider them an upgrade. You are correct regarding the US/NA E28 M5, standard E28 calipers. The E34 540i/M5 rear brakes are the setup to have in the rear.

Just my $.02.

Rich
gusgriff
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Post by gusgriff »

Thank you. This is the type of information I welcome.

You are correct I am going by the RealOEM.com diagrams. I should have checked the part number with a supplier. Four pistons per caliper will double the compression force on the rotors if the pressure supplied is the same. Even at a 25% lower pressure the force would be higher.

Do you know where I could get a better diagram of the M5 caliper? Are pistons on each side of the rotor?

Though this information changes my conclusion it does not invalididate it. There are questions that still need answering.


Do you know the output pressure to the pistons and if the brake hydraulic are indeed at a higher pressure and volume since the brake lines appear to be the same size?

Thank You again
Dana R
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Post by Dana R »

Have you been to the M535i.org site? Your questions should be answered well there. http://m535i.org/officers/ra/frame.html
Rich Euro M5
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Post by Rich Euro M5 »

You need to slow down and read more carefully when researching using RealOEM. The E28 535i and M5 utilize the same master cylinder. The different PN you found for the 535is is for non-ABS equipped E28s. The PN you listed for the M5 is the same part used on all ABS equipped E28s.

There are no other differences between the rest of the parts that I'm aware of except the flexible brake lines. The reason the M5 brake lines have a different PN is due to the length.

Finally you're making this too difficult. Forget all the mumbo jumbo about flow volume and pressure increases caused by orifice size. Both cars share all the same parts except the front calipers, rotors, and pads. Therefore any mention of things like flow rates is noise, and you're getting your self tied up in analysis paralysis. All you should be concerned about is the effect of the larger surface area of the M5 caliper pistons, and the slightly longer torque arm of the M5 caliper. If you really wanted to get anal, you would also want to know the differences in total surface area of the brake pads.

As "Dana R" mentioned, go to the M535i.org site. Chris Graff, who has a graduate degree in engineering, worked through all this years ago. At the time he had access to internal BMW engineering documents.

If you really want a best bang for your buck brake upgrade, stick with the E32 7er front brakes and E34 540i / M5 rear brakes. The E32 front brake pads share the same backing plate pattern as the E36 M3 brake pads. This significantly increases the number of brake pad options available for use.

Just my $.02.

Rich
gusgriff
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Post by gusgriff »

Thanks for the heads-up. This is not the first time RealOEM.com and my comprehension or lack-there-of led me down a deadend path.

Thank you. I had was slightly apprehensive posting these questions. There are some members who are not helpful, argue or make negative comments. I surmise these are the people who do not understand, do not want their opionions questioned or have some other agenda.

As long as their are members like you and others on this forum and other forums like bmwcca.org, I and others might just learn something. Thanks Again
Snakeyestx
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Post by Snakeyestx »

Welcome (if you're new here).

I just used E34 530 brakes as an upgrade and I've got to say, it feels just as good as the huge brake setup my E39 540-sport has.

Here's a buildup thread link that I just finished today :

http://www.mye28.com/viewtopic.php?t=75199

There's also a really good writeup on what other brakes you can use aside from E28 M5 brakes with many MANY options to choose from. I believe that's in the Tech FAQ section.
alpinacsi
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Post by alpinacsi »

You also mention flow volume. Brake systems do not work off of flow volume but more off of fluid displacement. The diameter of the lines do not change the function of the brakes except to say that the larger the diameter; the more expansion that can be expected and in some instances can lead to more pedal travel. Line pressures are a function of the caliper piston area, the mater cylinder size and amount of push rod (displacement) travel. Older fluid that has absorbed more moisture will compress more than fresh fluid and will require greater pushrod travel to acheive the same line pressures. The pedals in our cars have a fixed fulcrum point so the pedal travel and pressure required can only be adjusted by changing the calipers or master cylinder. A larger bore master cylinder will displace a higher volume at a lower pressure so if you have a pedal with a long travel after a caliper change the larger master will make the pedal feel stiffer and shorten the travel.

The other points mentioned about the calipers and masters is correct.
Rich Euro M5
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Post by Rich Euro M5 »

alpinacsi wrote:You also mention flow volume. Brake systems do not work off of flow volume but more off of fluid displacement.
Exactly - the fluid and the lines serve as the transmission line of the forces between the two interconnected cylinders.
alpinacsi wrote:Older fluid that has absorbed more moisture will compress more than fresh fluid and will require greater pushrod travel to acheive the same line pressures.
This is an inaccurate statement. A fluid isn't compressible, this is why it works well for the transmission of the applied force from the master cylinder piston to the brake caliper pistons. You are correct about it absorbing moisture, most brake fluids are hydroscopic and will absorb moisture. The problem with the moisture is that it causes corrosion and can also lapse into it's gaseous state (Boil) when the brakes get hot. When this happens you get brake sponginess and loss of brake pedal feel. If it's severe enough you can have a significant reduction in braking power.

Rich
alpinacsi
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Post by alpinacsi »

Any material can be compressed but maybe I should have worded it differently. When the moisture is introduced into the system it generally is found in the caliper end and since this is the area that is generally the heated end of the system; the fluid; heavily mixed with water at this point, will boil and allow the pedal to become "spongy". I guess that buy trying not to get to technical about it, I over simplified the original explination incorrectly.
vinceg101
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Post by vinceg101 »

Rich Euro M5 wrote: If you really want a best bang for your buck brake upgrade, stick with the E32 7er front brakes and E34 540i / M5 rear brakes. The E32 front brake pads share the same backing plate pattern as the E36 M3 brake pads. This significantly increases the number of brake pad options available for use.

Rich
When I was researching this upgrade (and boy I thought I got anal about the details), I came to conclusion that while the M5 setup is probably better all around, especially the E34 versions, they were more expensive to live with long term. M5 parts are harder to come by, more expensive when you find them, and limit your options. The E32/E34 Stage V upgrade is relatively inexpensive and plentiful and provide you with more options. Not to mention they will be cheaper in the long run.
wkohler
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Post by wkohler »

All rear E28 M5 calipers have a piston that is larger than the others by 1mm. It's to help with the brake bias. there's no difference in rotor size, etc.
Rich Euro M5
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Post by Rich Euro M5 »

alpinacsi wrote:Any material can be compressed but maybe I should have worded it differently. When the moisture is introduced into the system it generally is found in the caliper end and since this is the area that is generally the heated end of the system; the fluid; heavily mixed with water at this point, will boil and allow the pedal to become "spongy". I guess that buy trying not to get to technical about it, I over simplified the original explination incorrectly.
I agree you can compress a fluid as well as a solid, just not in this application. I should have used liquid vs fluid, since the term fluid can also be used to define gases as well as liquids. I think most of us with technical / science backgrounds understand what we're trying to explain, we get tripped up when we try to simplify the subject.

These types of discussions can devolve into pissing contests. A good example would be Rotational Momentum as applied to a flywheel and engine torque. I understand it from a mathematical / physics perspective, but refuse to even enter into the discussions I've seen on the forum.

Rich
Rich Euro M5
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Post by Rich Euro M5 »

wkohler wrote:All rear E28 M5 calipers have a piston that is larger than the others by 1mm. It's to help with the brake bias. there's no difference in rotor size, etc.
I've read this as well in the past, I know the caliper PNs are unique to the M5, but I'm not 100% certain about the piston size. Some day I'll measure the pistons on my M5 rear calipers and do the same with a set of stock calipers. From my own personal experience, the brake bias on the M5 isn't that great. Installing the E34 540i/M5 rear brakes makes a significant improvement.

Rich
Dana R
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Post by Dana R »

The big advantage with M5 front brakes over the e32 front brakes is not in the swept area, but in the brake feel from having a fixed 4 piston caliper vs. a floating caliper design. The thing I like least about upgrading the brakes to the e32/e34 540i setup is the slightly less firm brake pedal (on my old car it required more pedal travel which interfered with heel and toe downshifting) and the greater unsprung weight of the front calipers and rotors.

Question: Since I already have the e32 fronts, will the e34 535i rears, which are larger than the e28s, soften the pedal less than the e34 540i rears? Is the piston smaller? I think that the vented upgrade on the rears is overkill and counterproductive on anything but a heavily tracked car.
wkohler
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Post by wkohler »

Rich Euro M5 wrote:
wkohler wrote:All rear E28 M5 calipers have a piston that is larger than the others by 1mm. It's to help with the brake bias. there's no difference in rotor size, etc.
I've read this as well in the past, I know the caliper PNs are unique to the M5, but I'm not 100% certain about the piston size. Some day I'll measure the pistons on my M5 rear calipers and do the same with a set of stock calipers. From my own personal experience, the brake bias on the M5 isn't that great. Installing the E34 540i/M5 rear brakes makes a significant improvement.

Rich
I agree. I think it's one of the better, relatively inexpensive options.
mooseheadm5
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Post by mooseheadm5 »

Dana R wrote:Question: Since I already have the e32 fronts, will the e34 535i rears, which are larger than the e28s, soften the pedal less than the e34 540i rears? Is the piston smaller? I think that the vented upgrade on the rears is overkill and counterproductive on anything but a heavily tracked car.
The only difference is the vented rotors. The E34 535/30/25i rears have the same piston diameter as the 540i.
alpinacsi
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Post by alpinacsi »

I have noticed that many of the BMW calipers will have the piston size cast into the caliper for easy reference.

The M5/M6 calipers did indeed have a larger piston than the standard non m calipers but many of the cars have had replacements added over the years and some may not be sporting the original size.

I also ran into a issue with a rear upgrade when I bought a rear 540i caliper set and proceeded to rebuild them and had the wrong seals. I should have looked at the size stamped on the caliper as they were a 2mm smaller piston size. What I found was the very early 750il calipers were 38mm and the later ones and the e34 540 were larger.
alpinacsi
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Post by alpinacsi »

Rich Euro M5 wrote: I think most of us with technical / science backgrounds understand what we're trying to explain, we get tripped up when we try to simplify the subject.

Rich

:up:

and spelling, grammar and typing are not my strong suits
gusgriff
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Post by gusgriff »

Guys I am happy and surprised by all the dialog. This is more than I expected.

The discussion about the hydrodynamics and compresssible fluids is good reading. I misexplained my thoughts when I stated flow volume and pressure drop because there is no flow per say in the tubing. It is a displacement of the fluid mass. I was thinking more along the lines of controlling "flow" in and out of the calipers to balance or brake bias the system. With larger piston you need more displacement and without knowing whether this was controlled by orifice ports in the Master Cylinder, caliper or the sizing on the brake lines I was stumbling around for a explaination.

Even bolting on the big equipment ( calipers, pads & rotor ) is easy.With these items alone, you cannot claim to have near a M5, 735i or 540i brake system unless the other hydraulic system components can accomondate the upgrades. Most of us do not plan to change the remaining brake system equipment. If the remaining components cannot supply near the same hydraulic power or do not allow a similar balance and control on the braking you end up best wasting your money and possibly have a less desireable ride or worse creating an unsafe condition.
Rich Euro M5
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Post by Rich Euro M5 »

gusgriff wrote:Guys I am happy and surprised by all the dialog. This is more than I expected.

The discussion about the hydrodynamics and compresssible fluids is good reading. I misexplained my thoughts when I stated flow volume and pressure drop because there is no flow per say in the tubing. It is a displacement of the fluid mass. I was thinking more along the lines of controlling "flow" in and out of the calipers to balance or brake bias the system. With larger piston you need more displacement and without knowing whether this was controlled by orifice ports in the Master Cylinder, caliper or the sizing on the brake lines I was stumbling around for a explaination.

Even bolting on the big equipment ( calipers, pads & rotor ) is easy.With these items alone, you cannot claim to have near a M5, 735i or 540i brake system unless the other hydraulic system components can accomondate the upgrades. Most of us do not plan to change the remaining brake system equipment. If the remaining components cannot supply near the same hydraulic power or do not allow a similar balance and control on the braking you end up best wasting your money and possibly have a less desireable ride or worse creating an unsafe condition.
Pedal travel will increase when you install the E32 front / E34 540i/M5 rear big brakes when using the stock master cylinder.. It's not excessive but is noticeable. To restore the pedal to more normal travel, replace the master cylinder with the unit from the E32.

Rich
abdoosh00
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Post by abdoosh00 »

is it ok to upgrade to the E32 master cylinder and keep the E28 m535 callipers on??
mooseheadm5
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Post by mooseheadm5 »

Thanks, since most of you follow mye28.com you have seen the other replies. I was trying to find out the mechanism used to set the brake bias. Reading the replies as to the M5 upgrade the 1mm larger rear caliper piston will tend to equalize the bias.

This may seem a strange question but how much does suspension stiffness front to rear play in reducing nose dive? If brake bias is eqaul its effect should be minimal if none at all. I ask this because if you put brakes from another car on a car but not change the suspension is there an effect? For example; M5 brakes on my 535is will feel different since the suspension is different. I am assuming the M5 is stiffer.

Comments on the e32 and e34 brakes are appreciated.
I noticed your post over on the CCA forum- excellent questions.

When you brake, there will always be forward weight transfer. Front suspension stiffness definitely is a factor here, as is brake bias. If you have equal brake bias, you may not get the shortest stopping times since as the weight is transferred forward. You want forward brake bias to deal with the weight transfer, because as the weight moves forward from suspension compression the rear will lose traction, so you don't want them to lock up. The best system is to have a variable brake bias valve that increases forward bias as the rear suspension unloads, and indeed some older BMWs have this (I believe the 3.0CS among others.) Increasing the front spring rate and compression damping can reduce the weight transfer to the front wheels to the point where you can run equal bias, but this may not provide you with a desirable suspension setup handling wise. Of course the static weight distribution and ride height also play an important role in determining optimum brake bias. Now, in regards to the suspension stiffness difference between an M5 and 535is causing a difference, I would say that there would not be much difference noticed between the two cars with the same brakes since the suspension stiffness between the two cars is similar. If you have stiffer suspension in the front, you will have less brake dive.
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Post by cgraff »

mooseheadm5 wrote:
Thanks, since most of you follow mye28.com you have seen the other replies. I was trying to find out the mechanism used to set the brake bias. Reading the replies as to the M5 upgrade the 1mm larger rear caliper piston will tend to equalize the bias.

This may seem a strange question but how much does suspension stiffness front to rear play in reducing nose dive? If brake bias is eqaul its effect should be minimal if none at all. I ask this because if you put brakes from another car on a car but not change the suspension is there an effect? For example; M5 brakes on my 535is will feel different since the suspension is different. I am assuming the M5 is stiffer.

Comments on the e32 and e34 brakes are appreciated.
I noticed your post over on the CCA forum- excellent questions.

When you brake, there will always be forward weight transfer. Front suspension stiffness definitely is a factor here, as is brake bias. If you have equal brake bias, you may not get the shortest stopping times since as the weight is transferred forward. You want forward brake bias to deal with the weight transfer, because as the weight moves forward from suspension compression the rear will lose traction, so you don't want them to lock up. The best system is to have a variable brake bias valve that increases forward bias as the rear suspension unloads, and indeed some older BMWs have this (I believe the 3.0CS among others.) Increasing the front spring rate and compression damping can reduce the weight transfer to the front wheels to the point where you can run equal bias, but this may not provide you with a desirable suspension setup handling wise. Of course the static weight distribution and ride height also play an important role in determining optimum brake bias. Now, in regards to the suspension stiffness difference between an M5 and 535is causing a difference, I would say that there would not be much difference noticed between the two cars with the same brakes since the suspension stiffness between the two cars is similar. If you have stiffer suspension in the front, you will have less brake dive.
That is completely wrong.

Weight transfer (wrong terminology too, its actually should LOAD transfer) does NOT change with spring rate and compression damping. Load transfer is a function purely of center of gravity, wheelbase, and wheel track. That is the first order calculation that sets brake bias.

Also, BMWs do NOT have a variable brake bias valve.

'Brake dive' is a function of spring rate due to the compression of spring from the reactive forces under the load transfer. The softer the spring the more travel (spring compression) you have for the same force.

-Chris
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Post by mooseheadm5 »

cgraff wrote:
mooseheadm5 wrote:
Thanks, since most of you follow mye28.com you have seen the other replies. I was trying to find out the mechanism used to set the brake bias. Reading the replies as to the M5 upgrade the 1mm larger rear caliper piston will tend to equalize the bias.

This may seem a strange question but how much does suspension stiffness front to rear play in reducing nose dive? If brake bias is eqaul its effect should be minimal if none at all. I ask this because if you put brakes from another car on a car but not change the suspension is there an effect? For example; M5 brakes on my 535is will feel different since the suspension is different. I am assuming the M5 is stiffer.

Comments on the e32 and e34 brakes are appreciated.
I noticed your post over on the CCA forum- excellent questions.

When you brake, there will always be forward weight transfer. Front suspension stiffness definitely is a factor here, as is brake bias. If you have equal brake bias, you may not get the shortest stopping times since as the weight is transferred forward. You want forward brake bias to deal with the weight transfer, because as the weight moves forward from suspension compression the rear will lose traction, so you don't want them to lock up. The best system is to have a variable brake bias valve that increases forward bias as the rear suspension unloads, and indeed some older BMWs have this (I believe the 3.0CS among others.) Increasing the front spring rate and compression damping can reduce the weight transfer to the front wheels to the point where you can run equal bias, but this may not provide you with a desirable suspension setup handling wise. Of course the static weight distribution and ride height also play an important role in determining optimum brake bias. Now, in regards to the suspension stiffness difference between an M5 and 535is causing a difference, I would say that there would not be much difference noticed between the two cars with the same brakes since the suspension stiffness between the two cars is similar. If you have stiffer suspension in the front, you will have less brake dive.
That is completely wrong.

Weight transfer (wrong terminology too, its actually should LOAD transfer) does NOT change with spring rate and compression damping. Load transfer is a function purely of center of gravity, wheelbase, and wheel track. That is the first order calculation that sets brake bias.

Also, BMWs do NOT have a variable brake bias valve.

'Brake dive' is a function of spring rate due to the compression of spring from the reactive forces under the load transfer. The softer the spring the more travel (spring compression) you have for the same force.

-Chris
Thanks for the corrections. Doesn't the change in CG caused by suspension compression play an important role here, though? Once you hit the brakes and the nose dives, the CG changes, does it not?
I may have misremembered the brake proportioning valve on the CS. It is adjustable, but maybe it isn't variable. I know I have seen a variable one somewhere, but it has been such a long time so I must have gotten mixed up. I know they do exist, though, but hell if I can remember what I saw it on now.
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