Fixed versus Sliding brake calipers

[JimD]

This topic got buried and beat up in the recent 128 versus 135 thread so maybe I should drop this - or somebody should delete the thread. I believe the bottom line is it depends a lot more on how well the brakes are engineered and built than it does whether they slide or are fixed.

For those who didn't follow that discussion or want a brief explanation of the difference, brake calipers can either be fixed in position and have pistons on both sides of the disc or they can have pistons on only one side (usually just one piston) and slide so that the pads on both sides of the disc (or rotor) engage the disc.

The 135i have 6 piston calipers built by brembo. Unfortunately there are reports of these brakes overheating to the point of caliper damage in heavy track use. But race cars often have fixed position brakes and brembo is a big name brand. There is a question if the 135i brakes are well executed (at least in my mind) but the fact that this design seems to be preferable for performance cars is a factor in favor of this design. You don't have to depend on the caliper sliding and logically you will get more even pressure on the pads with fixed calipers. You can even do things like adjust the size of the pistons on the leading and trailing edge to further even out brake wear.

On the other hand, the 1M and the M3 use a sliding caliper brake. I looked it up on RealOEM to be sure. So at least some high performance cars use a sliding caliper design like the 128i.

My main point is just that either type of brake can perform at a high level and either type of brake can have issues. I think the 135i fixed design is preferable but not if it is engineered such that the pistons may stick if you work the brakes really hard at a track. I don't plan to switch my 128i to a fixed design, and the fact that the 1M and M3 both have sliding calipers seems to put me in good company.

[ShocknAwe]

My question has always been how do the 135i brembos perform once all the heat sensitive parts (pistons, boots, seals) have been replaced in the upgrade? It's well documented that there is an engineering flaw in the 135i "big brakes."

Link to 1addicts thread on this:
http://www.1addicts.com/forums/showthread.php?t=824046

I actually prefer sliding calipers. I find them easier to work on and slider pins are easy to replace as well. It could just be a comfort issue through my mechanical know-how, or it could be a true simplicity/functionality thing. I'm not in a position to say which it is.

[JimD]

Originally Posted by ShocknAwe

My question has always been how do the 135i brembos perform once all the heat sensitive parts (pistons, boots, seals) have been replaced in the upgrade? It's well documented that there is an engineering flaw in the 135i "big brakes."

Link to 1addicts thread on this:
http://www.1addicts.com/forums/showthread.php?t=824046

I actually prefer sliding calipers. I find them easier to work on and slider pins are easy to replace as well. It could just be a comfort issue through my mechanical know-how, or it could be a true simplicity/functionality thing. I'm not in a position to say which it is.

I've never had a car with fixed calipers so I've never changed pads on one. I've seen reports that it isn't bad but sliders are definitely pretty simple. I still have a SUV with rear drums and have had many cars with drum brakes over the years. Discs in general are definitely easier than drums. Just too many parts to drums and also frequently difficulty getting the drums off.

I think one reason people look down on sliders is they're cheaper to make. I don't mind that as long as they work the same. I've noticed the pads usually don't wear at the same rate on sliders, the pad contacting the piston wears more, but the car stops fine and I don't have to replace brakes much since I have a manual transmission and normal duty is pretty light.

[Stvee]

Originally Posted by JimD

I've never had a car with fixed calipers so I've never changed pads on one. I've seen reports that it isn't bad but sliders are definitely pretty simple. I still have a SUV with rear drums and have had many cars with drum brakes over the years. Discs in general are definitely easier than drums. Just too many parts to drums and also frequently difficulty getting the drums off.

I think one reason people look down on sliders is they're cheaper to make. I don't mind that as long as they work the same. I've noticed the pads usually don't wear at the same rate on sliders, the pad contacting the piston wears more, but the car stops fine and I don't have to replace brakes much since I have a manual transmission and normal duty is pretty light.

I haven't had to do it on this car yet, but changing the brake pads on my Evo 9 (also had brembos) was way easier than a sliding caliper. You take two pins out and then a clip that holds the pads comes off. The pads just pull out through the top of the caliper after that. Simple as it gets.

Pretty sure they are made that way on purpose to make it easy for people tracking their cars to switch pads.

[chris82]

I do remember a post by one member/team that raced their 135i that had problems with their brakes but other than that how many more are there?

[Stvee]

Originally Posted by Chrisar82

I do remember a post by one member/team that raced their 135i that had problems with their brakes but other than that how many more are there?

A bunch of people have had problems with the pistons/seals cracking after hard track use. BMW just cheaped out in this area. I think the upgrade kit to replace the pistons and seals on the front and back is like 500 bucks.

After that, they're good to go from what I've seen.

[3002 tii]

Originally Posted by Chrisar82

I do remember a post by one member/team that raced their 135i that had problems with their brakes but other than that how many more are there?

Part of that was attributed to using the wrong pad size (custom cut). Since then there have been a few aftermarket pad options meant specifically for the 135i. But you would still probably need to rebuild the caliper every other year depending on how often you track the car.

[davis449]

Originally Posted by Stvee

A bunch of people have had problems with the pistons/seals cracking after hard track use. BMW just cheaped out in this area. I think the upgrade kit to replace the pistons and seals on the front and back is like 500 bucks.

After that, they're good to go from what I've seen.

See, this is good information that should've been brought to the other thread, because "racecardriverexpert", in the other thread, was saying upgrades to the stock 128i brakes made everything just peachy for heavy track use. So he probably spent at min. $500 on his stock 128i brakes to make them "track ready". Therefore, what this says to me is that ~$500 gets the 135i brakes "track ready" and due to all the things mentioned in the other thread that make the 135i brakes superior to those of the 128i (heat dissipation, etc.) will, thus, allow the 135i's 6 piston OEM brakes, indeed, perform better than the brakes on a 128i under heavy track use. Therefore "racecardriverexpert" has pretty much been proven wrong.

Awesome. /thread for me.

[FactorX81]

How well a cars brakes perform on a track is a function of how hard the track is on the brakes, how hard the driver is on the brakes(skill and experience dictate this), and how well the brake components can absorb then dissipate the heat. The only brakes that do exceptionally well on the track are brakes which are designed to do so ex real bbk. All street cars have compromises when it comes to brakes. I would suggest tracking your car and seeing if the brakes don't hold up then make changes if necessary. Many of the reports of the 135 brakes pistons failing had pads that didn't fit right or compounds that overheated the rubber components because of clearances with aftermarket pads extra shims etc. Some folks have complained about paint discoloration due to heat cycling. Not everyone who tracks their car has these experiences not every track is super hard on brakes and most people are not race car drivers.

Fixed vs floating
Both can be done well if properly sized but there is a reason fixed are used in bbks and all the new m cars. Fixed calipers allow for a more consistent pressure application across the pad which should also equate to even pad wear and good pedal feel. Floating calipers are great because they are inexpensive, easy to maintain, low moving parts and can provide plenty of braking force. Maintenance wise I don't think the 135 brakes are easier to change because you have to remove the caliper in front to change the pads.

[Kgolf31]

Originally Posted by davis449

See, this is good information that should've been brought to the other thread, because "racecardriverexpert", in the other thread, was saying upgrades to the stock 128i brakes made everything just peachy for heavy track use. So he probably spent at min. $500 on his stock 128i brakes to make them "track ready". Therefore, what this says to me is that ~$500 gets the 135i brakes "track ready" and due to all the things mentioned in the other thread that make the 135i brakes superior to those of the 128i (heat dissipation, etc.) will, thus, allow the 135i's 6 piston OEM brakes, indeed, perform better than the brakes on a 128i under heavy track use. Therefore "racecardriverexpert" has pretty much been proven wrong.

Awesome. /thread for me.

I don't really want to argue, so I'll just keep this thread on track. Of course, as we all know, you've done SO much to your car and fine tuning you know everything there is to know...right?

I'll just say, there are other factors than just brakes. My 128i will no doubt, stop faster than my Z4M with same pad compound.

As well, in stock form...the 128i vs 135i calipers will perform the same because you have different limiting factors other than the rotor and caliper


PS - There are inherit flaws with 135i stock calipers that are well documented. They cannot handle heat

[JimD]

It doesn't cost $500 to put better track ready pads on a 128i. Different rotors will cost about the same for either car. I think the 135i is probably fine for street use but if I had one, I would want to keep an eye on the pistons and seals. But if I wanted to track a 135i, I would definitely upgrade the pistons but I don't know if that fixes it or not. I've seen reports after 1 or 2 track sessions but not more extensive use. I hope the kits take care of it but having to spend $500 to fix a problem you shouldn't have is unfortunate.

I think the F82 (m4) uses fixed calipers but the e92 M3 and 1M are sliders. I think for a car used mainly on the street, it doesn't make a lot of difference - as long as they are well engineered. 128s actually seem to be engineered better than 135i.

[FactorX81]

Originally Posted by JimD

But if I wanted to track a 135i, I would definitely upgrade the pistons but I don't know if that fixes it or not.

Or you could just track the car and check whether the brakes were damaged like many people do without issue. You are insinuating that a tracked 135 will instantly have damaged brakes which is not the case.

M4 has 6 piston fixed calipers. The E9x M had large floaters that were often criticized as not being track worthy.

[fboutlaw]

Not sure where this thread was intended to go.

Fixed caliper is preferred for all track use. You find it all sports cars.

Floating caliper systems are cheaper to manufacture and hence found on budget vehicles. Due to friction on the race to the outside pad, you will always, no matter what you do, have uneven wear on your pads and therefore rotors.

As mentioned on the thread, the 135 brakes aren't brilliantly designed, but can be used for moderate track use without issue. Heavy track use is a problem as the rotor is too thin, doesn't effectively cool, and stays way hotter than it should causing excessive wear on the pads and rotors. If you're building a track car, you're going to want a proper set of fixed calipers from brembo, stoptech, AP racing, or any of the good setups. Buying it as part of an engineered BBK is the best option.

I've tried the stock setup with OEM pads and cool carbons on the track and it got really scary due to uneven pad deposits on the rotors causing shuddering under heavy braking.

Swap out to stoptech BBK and it's brilliant. The stock compound is fine in the rear, but the fronts do require dedicated track pads to handle the heat. I'm on PFC pads up front, and couldn't be happier.

If you're worried about the brakes, you aren't driving hard enough for it to matter. If they've already scared you, you've already invested in a proper BBK.

If you're cheap and want the car to be OK for HPDE days, unbolt the dust shields on the back of the knuckles for extra cooling and you can survive a few events.

[chris82]

Originally Posted by JimD

It doesn't cost $500 to put better track ready pads on a 128i. Different rotors will cost about the same for either car. I think the 135i is probably fine for street use but if I had one, I would want to keep an eye on the pistons and seals. But if I wanted to track a 135i, I would definitely upgrade the pistons but I don't know if that fixes it or not. I've seen reports after 1 or 2 track sessions but not more extensive use. I hope the kits take care of it but having to spend $500 to fix a problem you shouldn't have is unfortunate.

I think the F82 (m4) uses fixed calipers but the e92 M3 and 1M are sliders. I think for a car used mainly on the street, it doesn't make a lot of difference - as long as they are well engineered. 128s actually seem to be engineered better than 135i.

Yea here is the thing, these reports of fried pistons and such are not common. In fact, other than that one guy/team, I haven't seen any other reports of them getting muffed up (I haven't, maybe some of you have though). That being said, I think the issue is irrelevant for street only and lightly tracked cars. If you plan on it being your track beater, then you should probably get those pistons replaced or keep an eye on them. That's my take on it.

[MightyMouseTech]

Originally Posted by Kgolf31

I'll just say, there are other factors than just brakes. My 128i will no doubt, stop faster than my Z4M with same pad compound.

Exactly. The tires stop the car, not the brakes.

[The HACK]

I'm about to end this thread/discussion once and for all.

Brakes work as a SYSTEM. Any weak point in the system will get exposed in heavy track use. It doesn't matter if you have a 8 piston caliper forged out of un-obtainium, if that caliper sits on a 11.5" rotor on a 3,500lbs car that's capable of pushing 400 hp, you'll have problems with the brakes on track, PERIOD.

So this whole discussion of whether or not a fixed caliper is better than a sliding caliper? Moot. Because the caliper only makes up 1/3rd of the equation.

Let's go ALL THE WAY back to the basics.

Brakes are designed to convert the kinetic energy of the vehicle moving at speed into HEAT (and sometimes, noise and light, but that's up for another debate), by stopping the rotating mass that is know as the wheels and tires. How well that works, depends on multiple factors, but let's concentrate on the ONE that we're talking about here...

Tell me, out of the three main components of a brake system (caliper, rotor, and friction material, aka pads), which one's primary responsibility is to dissipate said heat?

It ain't the calipers.

Now that I got that out of the way, I'm going to go a little bit into depth as to the pros and cons of the two different caliper design, then I'm going to tell you WHY the 135i brakes suck.

Sliding calipers

Pros
Smaller package: Since sliding calipers only has piston(s) on the inside, the outside profile of the caliper can be made only as thick as necessary to hold the outboard pad.
Easy mounting: Sliding caliper design can be made to mount to a variety of hub locations and rotor size. Unlike fixed calipers, which can only be mount to rotors of a small range, a single sliding caliper part number can be made to fit a very wide range of rotor sizes and different hub mount. For example, the sliding calipers on the E36 M3, E46 M3, E46 M3 CSL, E46 330i/Ci ALL use the same interchangeable caliper, but they all have different hub designs, brake caliper mounting points, and different rotor sizes.
Cheap to make: A sliding caliper only needs one piston, therefore don't need to be machined and can be cast out of cast iron.

Cons
Limited brake pad shape: Because of the bracket and caliper combo, the shape of each brake pad is almost exclusive to that caliper. You won't have the flexibility to make one single pad shape that fits multiple calipers.
Inherent flex: Because sliding calipers mount to a sliding mechanism that allows the caliper to move, there's an inherent "pivot" point for the caliper to flex on.
Heavy: Cast iron is heavier than machined aluminum. There's just no way around it.

Fixed calipers

Pros
Rigid body: Fixed calipers are inherently more rigid because the bracket is not part of the operation, and since the only moving parts are the pistons, it can be made far more rigid than sliding calipers.
Light weight: Due to that inherent rigidness of the fixed caliper design, it can be made of machined aluminum, thus allowing a significant amount of weight saving AND still maintain more rigidity than sliding caliper design.
Better distribution of brake force across pad surface: Again, since fixed calipers don't have moving parts outside of the caliper pistons, the calipers themselves do not flex as much under heavy forces supplied by the caliper pistons, and the forces are distributed across multiple pistons from both sides of the piston body therefore the actual forces applied under braking are distributed far more evenly across the friction surface

Cons
Inefficient use of space: Fixed calipers REQUIRE space on the outboard side to accommodate for the depth of another set of calipers, plus the hardware and passages cut and machined into the piston body to allow fluids to move across BOTH SIDES of caliper.
Cost: Fixed calipers are inherently larger, therefore requiring the use of a much lighter, much more expensive material...Aluminum. In addition, the pistons in the calipers are more expensive and typically are made of stainless steel to prevent corrosion, and each piston require additional seals and machining leading to a much higher cost to manufacture
"Inflexible" application: Fixed calipers are designed to accommodate only a certain range of rotor radius, so in a mass production capacity, the way the pistons are arranged and the curvature of the caliper dictates the size of the rotor you can use with each caliper.

So, as you can see, there are clear advantages to each. Sliding calipers are cheaper to make, easier to package. Fixed calipers offer distinct performance advantages but at a cost. So why does the 135i brakes suck compared to the ///M brakes, despite the ///Ms using sliding calipers and the 135i uses brembo fixed calipers?

Because brakes are a SYSTEM.

First, because fixed calipers are more expensive to make, BMW cut some very significant corners with Brembo to get the calipers down to a reasonable price. You can't make it out of cast iron (too heavy), you can't buy enough of them and fit them on EVERY car you make to bring the cost further down, so what does BMW do? Use cheap seals. Cut corners on thermal protection on the pistons. Gotta find ways to make it cheap enough so they can still claim to put "Brembos" on their car.

Second? They put a 12" rotor on a car that weighs north of 3,300 lbs that can put out in excess of 300 HP, because it's cheaper to make a 1 piece, 12" rotor than to equip every 135i with a floating 2 piece, 14" rotor. Go ahead. Price out the difference between the 135i's brake rotor vs. M3's brake rotor. This is where the "system" comes in. You have to convert all that kinetic energy into heat, and the heat has to escape somewhere otherwise the whole system will melt. And melt it did. M3's 2 piece, center mounted FLOATING ROTORS with it's massive 14" rotor surface allows it to evacuate all that heat much quicker, while the 2 piece rotor design with the open, center mount allow it to draw more air in through the internal air vents to cool down the heat sink, I mean, rotors quicker too.

And since the ///Ms use a sliding caliper, they can afford to put in much better caliper piston seal with a much larger single sliding piston to allow for more surface area on the piston to prevent too much heat from building up in each piston, while the smaller individual pistons on the 135i means, as the heat builds up faster from the smaller rotors, the smaller surface area of each piston means more heat is transmitted through the individual piston.

Problem number 1 for the 135i, is BMW chose a rotor that's too small and too inefficient to properly evacuate heat fast enough. Problem number 2 is, since that heat has no-where to go, the caliper pistons absorbed the brunt of that heat and the seals go. So while the fixed calipers are technically superior (and likely more expensive), the SYSTEM as a whole is inferior at it's ability to convert kinetic energy into heat.

The best solution, is, obviously, a large two piece floating rotor with a fixed multi piston caliper. But the problem inherent in that is, floating two piece rotors are expensive, and the larger they are, the more expensive they get, because you can't just cast a whole rotor in one shot, you have to cast the rotor ring, add the cost of the fastener hardware, the time and "labor" to assemble, then the cost to cast/machine the hub. Good example is the MZ4 rotors. They're around $300 each. EACH. To change all four rotors, just on parts alone, is over $1,200. The 135i rotor is what, around $100?

That's why when you get into racing applications? Where result is far more important than the money you have to spend? And application is on just a handful of cars? You'll see fixed calipers, but not just fixed calipers, but fixed calipers with large, oversized two piece floating rotors and racing friction compounds with high metallic content (because the high metallic content creates higher friction coefficient AND better heat capacity than organic/ceramic compound). But when you have to do that for thousands of cars? Tens of thousands? HUNDREDS of thousands?

It adds up.

[The HACK]

Originally Posted by Kgolf31

I'll just say, there are other factors than just brakes. My 128i will no doubt, stop faster than my Z4M with same pad compound.

But does it stop REPEATEDLY faster than the Z4M with the same compound?

[Suprgnat]

Originally Posted by The HACK

Second? They put a 12" rotor on a car that weighs north of 3,300 lbs that can put out in excess of 300 HP,

Minor correction. 135i rotors are 338mm or 13.31" (and they're two piece as they have an aluminum hat, though not floating)

[Overpar56]

Originally Posted by The HACK

I'm about to end this thread/discussion once and for all.

Brakes work as a SYSTEM. Any weak point in the system will get exposed in heavy track use. It doesn't matter if you have a 8 piston caliper forged out of un-obtainium, if that caliper sits on a 11.5" rotor on a 3,500lbs car that's capable of pushing 400 hp, you'll have problems with the brakes on track, PERIOD.

So this whole discussion of whether or not a fixed caliper is better than a sliding caliper? Moot. Because the caliper only makes up 1/3rd of the equation.

Let's go ALL THE WAY back to the basics.

Brakes are designed to convert the kinetic energy of the vehicle moving at speed into HEAT (and sometimes, noise and light, but that's up for another debate), by stopping the rotating mass that is know as the wheels and tires. How well that works, depends on multiple factors, but let's concentrate on the ONE that we're talking about here...

Tell me, out of the three main components of a brake system (caliper, rotor, and friction material, aka pads), which one's primary responsibility is to dissipate said heat?

It ain't the calipers.

Now that I got that out of the way, I'm going to go a little bit into depth as to the pros and cons of the two different caliper design, then I'm going to tell you WHY the 135i brakes suck.

Sliding calipers

Pros
Smaller package: Since sliding calipers only has piston(s) on the inside, the outside profile of the caliper can be made only as thick as necessary to hold the outboard pad.
Easy mounting: Sliding caliper design can be made to mount to a variety of hub locations and rotor size. Unlike fixed calipers, which can only be mount to rotors of a small range, a single sliding caliper part number can be made to fit a very wide range of rotor sizes and different hub mount. For example, the sliding calipers on the E36 M3, E46 M3, E46 M3 CSL, E46 330i/Ci ALL use the same interchangeable caliper, but they all have different hub designs, brake caliper mounting points, and different rotor sizes.
Cheap to make: A sliding caliper only needs one piston, therefore don't need to be machined and can be cast out of cast iron.

Cons
Limited brake pad shape: Because of the bracket and caliper combo, the shape of each brake pad is almost exclusive to that caliper. You won't have the flexibility to make one single pad shape that fits multiple calipers.
Inherent flex: Because sliding calipers mount to a sliding mechanism that allows the caliper to move, there's an inherent "pivot" point for the caliper to flex on.
Heavy: Cast iron is heavier than machined aluminum. There's just no way around it.

Fixed calipers

Pros
Rigid body: Fixed calipers are inherently more rigid because the bracket is not part of the operation, and since the only moving parts are the pistons, it can be made far more rigid than sliding calipers.
Light weight: Due to that inherent rigidness of the fixed caliper design, it can be made of machined aluminum, thus allowing a significant amount of weight saving AND still maintain more rigidity than sliding caliper design.
Better distribution of brake force across pad surface: Again, since fixed calipers don't have moving parts outside of the caliper pistons, the calipers themselves do not flex as much under heavy forces supplied by the caliper pistons, and the forces are distributed across multiple pistons from both sides of the piston body therefore the actual forces applied under braking are distributed far more evenly across the friction surface

Cons
Inefficient use of space: Fixed calipers REQUIRE space on the outboard side to accommodate for the depth of another set of calipers, plus the hardware and passages cut and machined into the piston body to allow fluids to move across BOTH SIDES of caliper.
Cost: Fixed calipers are inherently larger, therefore requiring the use of a much lighter, much more expensive material...Aluminum. In addition, the pistons in the calipers are more expensive and typically are made of stainless steel to prevent corrosion, and each piston require additional seals and machining leading to a much higher cost to manufacture
"Inflexible" application: Fixed calipers are designed to accommodate only a certain range of rotor radius, so in a mass production capacity, the way the pistons are arranged and the curvature of the caliper dictates the size of the rotor you can use with each caliper.

So, as you can see, there are clear advantages to each. Sliding calipers are cheaper to make, easier to package. Fixed calipers offer distinct performance advantages but at a cost. So why does the 135i brakes suck compared to the ///M brakes, despite the ///Ms using sliding calipers and the 135i uses brembo fixed calipers?

Because brakes are a SYSTEM.

First, because fixed calipers are more expensive to make, BMW cut some very significant corners with Brembo to get the calipers down to a reasonable price. You can't make it out of cast iron (too heavy), you can't buy enough of them and fit them on EVERY car you make to bring the cost further down, so what does BMW do? Use cheap seals. Cut corners on thermal protection on the pistons. Gotta find ways to make it cheap enough so they can still claim to put "Brembos" on their car.

Second? They put a 12" rotor on a car that weighs north of 3,300 lbs that can put out in excess of 300 HP, because it's cheaper to make a 1 piece, 12" rotor than to equip every 135i with a floating 2 piece, 14" rotor. Go ahead. Price out the difference between the 135i's brake rotor vs. M3's brake rotor. This is where the "system" comes in. You have to convert all that kinetic energy into heat, and the heat has to escape somewhere otherwise the whole system will melt. And melt it did. M3's 2 piece, center mounted FLOATING ROTORS with it's massive 14" rotor surface allows it to evacuate all that heat much quicker, while the 2 piece rotor design with the open, center mount allow it to draw more air in through the internal air vents to cool down the heat sink, I mean, rotors quicker too.

And since the ///Ms use a sliding caliper, they can afford to put in much better caliper piston seal with a much larger single sliding piston to allow for more surface area on the piston to prevent too much heat from building up in each piston, while the smaller individual pistons on the 135i means, as the heat builds up faster from the smaller rotors, the smaller surface area of each piston means more heat is transmitted through the individual piston.

Problem number 1 for the 135i, is BMW chose a rotor that's too small and too inefficient to properly evacuate heat fast enough. Problem number 2 is, since that heat has no-where to go, the caliper pistons absorbed the brunt of that heat and the seals go. So while the fixed calipers are technically superior (and likely more expensive), the SYSTEM as a whole is inferior at it's ability to convert kinetic energy into heat.

The best solution, is, obviously, a large two piece floating rotor with a fixed multi piston caliper. But the problem inherent in that is, floating two piece rotors are expensive, and the larger they are, the more expensive they get, because you can't just cast a whole rotor in one shot, you have to cast the rotor ring, add the cost of the fastener hardware, the time and "labor" to assemble, then the cost to cast/machine the hub. Good example is the MZ4 rotors. They're around $300 each. EACH. To change all four rotors, just on parts alone, is over $1,200. The 135i rotor is what, around $100?

That's why when you get into racing applications? Where result is far more important than the money you have to spend? And application is on just a handful of cars? You'll see fixed calipers, but not just fixed calipers, but fixed calipers with large, oversized two piece floating rotors and racing friction compounds with high metallic content (because the high metallic content creates higher friction coefficient AND better heat capacity than organic/ceramic compound). But when you have to do that for thousands of cars? Tens of thousands? HUNDREDS of thousands?

It adds up.

How long did this take to type out?

[Kgolf31]

Originally Posted by The HACK

But does it stop REPEATEDLY faster than the Z4M with the same compound?

Lol no way

BTW - You probably upset all of the 135i owners. Beware of the wrath.

[lowbudgethero]

Another thing i'm surprised no one has mentioned the difference in speeds when you start braking of the 135i(especially a lightly tuned 135i) compared to the 128i after a straightaway. The point being made by the 128i owners makes sense, disregarding the engineering problems of the 135i's pistons and seals it's simply the brakes are just less balanced with both cars. It only gets worse when you get even more power to the 135i.

[The HACK]

Originally Posted by Overpar56

How long did this take to type out?

The truth is most of that was copied and pasted from stuff that I've already said on other forums, or info readily available from a simple Google search. I didn't really have to come up with much in terms of real original thought.

For someone who's touted the virtues of the brakes on the MZ4 Coupe and had been tracking extensively over 7 years on the stock sliding caliper set-up, I finally ponied up and got fixed calipers for all 4 corners. Why? Because it IS better.

But in order to do so, I've sacrificed the ability to run my preferred wheel and tire set-up because the front now requires a 5mm spacer to fit. And to be completely honest? The fix calipers did not significantly alter the braking performance. If we're to go strictly by fade resistance and stopping distance, it changes NOTHING. What the fixed caliper gave me was easy access to swap pads, better pad choices, significant improvement in pad life, pedal feel, and ease of modulation, and a far more consistent result on track.

But on objective braking performance data? ZERO difference.

I would like to surmise that my average lap time probably decreased with the fixed caliper upgrade, but since the upgrade literally forced some major changes in set-up (wheel/tires, camber, toe), it is impossible to quantify at this point.