Z4m40i
Well-Known Member
- First Name
- Justin
- Joined
- Nov 30, 2023
- Threads
- 9
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- 156
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- 175
- Location
- Salt Lake City
- Car(s)
- 2020 BMW z4 m40i, 2020 BMW X7 40i
- Thread starter
- #1
Long time reader and wanted to give back to the community. I have a BMW z4 m40i that I occasionally track. I notice my stock brakes fading. The easiest answer was to switch out to more aggressive pads and higher temp fluid, but I disliked the idea of having to swap out pads between track and street driving. I wanted to find a middle of the road compromise that was friendly enough on the street yet capable on the track. This topic is not about the pros and cons of a BBK, but more so about what options you have in BMWâs catalog for âupgradesâ.
The stock brake system is very capable, even though the z4 weighs in a couple hundred pounds more to the supra. During corner balancing, my car weighs in at ~3750lbs. I use the 374mm front rotors with EBC yellow pads which I find to be the perfect upgrade that performs well on the street and track.
Front brakes:
To begin, the front M âsportâ brakes come in 3 different sizes depending on the chassis. The brake calipers are stamped in the back that indicate piston count and size, and what size rotor it will fit on. For example, the stock brakes are labeled â4x40-44/348/36â and all variants are made by Brembo. The mounting holes measure 14mm apart center to center, and all interchangeably mount on the wheel hub (aka swivel bearing in BMW terms)
BMWâs marketing lingo: M sport vs M performance. I hate how much BMW has diluted the use of M branding. If youâre like me, you didnât realize there is a difference between âsportâ and âperformanceâ. These are not interchangeable terms without context. What is âperformanceâ for one chassis, is âsportâ for another. For example, the âM Performanceâ brake for the g20 3 series upgrades the front brakes to 374x36 rotors, but keeps the same exact rear brake caliper size as the âm sportâ on the g20 cars. They just get painted red, come with dimpled rotors, and cost about 3k for the package. To make things more confusing is that these brakes are equivalent to the âM Sportâ of the 5 series g30!
The âM performanceâ package for the g30, which upgrades the brakes to 395x36 rotors, is the same brakes on the âM sportâ on the x5 g05 and x7 g07 SUVâs!
One thing to consider is that âM Performanceâ brakes are a dealer addon whereas âM Sportâ is a factory configuration (S2NHA). Also note that US and euro models will have slightly different offerings, so this will mostly focus on US models.
Part numbers can vary for components that are technically the same. For example the brake caliper on G20 M performance brake package is painted âredâ and is EXACTLY the same as the g30 M Sport but itâs painted blue- thus a different part number. The cost of the G20 m performance package is $$$ more compared to sourcing g30 m sport calipers.
Please consider that part numbers have been updated throughout time. There may be other newer/older part numbers that should be interchangeable.
The master cylinder is the same on all 3 series models for US Spec only. The z4 shares the same master cylinder as the 3 series, which I assume is the same for the supra. The brake servo/booster is bespoke to the z4/supra only. Since piston sizes are the same regardless of the caliper size, brake pedal feel should virtually be the same. If you live outside of the US, the master cylinder will need to be upgraded and BMW calls for it to be coded as well.
348x36
Rear brakes:
The rears are a little tricky. Factory M sport brakes for the z4/supra/g20 use a 345mmx24 rotor. The caliper is manufactured by Mando. For most other chassis models, they will also use a 345x24 rotor, but use TRW as the manufacturer. Piston size is exactly the same. While these are MOSTLY interchangeable, there are two key differences.
The TRW caliper body can accommodate both a 345x24 AND a 370x24 rotor. The only change is the caliper carrier bracket to accommodate larger pads and rotors. While the piston sizes are the same between the Mando and TRW caliper, the Mando caliper ONLY fits a 345mm rotor and cannot simply benefit from a caliper bracket change like the TRWâs can. Having specâed with Mando calipers, you will need to upgrade to any TRW caliper body, but with caliper carrier brackets specâed for 370mm rotors.
Additionally, the ebrake motors are physically different. While the mounting holes for the motor onto the caliper body are the same, the mating surface is completely different. The motors themselves cannot be swapped between a Mando and TRW caliper. This makes things a little tricky because the plug bodies are keyed differently. The supra/z4 uses a blue male plug, and TRW caliper will use a white male plug. The outer plug housing is the same âDâ shape. Fortunately, they are pinned exactly the same and labeled accordingly (male and female plug will be labeled with a â1â and â2â) In order to maintain the factory use of the ebrake, you will need to modify the female plug housing of the ebrake motor. This can be achieved by heating up a flat head screw driver, and âmeltingâ off the keyed slots of the female plug housing in the ebrake motor. Even after modifying the ebrake housing, the plugs will still clip into eachother so there is no issue with the plug coming off.
see the black "slots" in the plug housing that need to be melted/grinded off.
Caliper carrier brackets measure 9mm between the center of the mounting holes.
Similar to the fronts, the rears are also stamped with sizes.
The TRW calipers come in unpainted, blue, and red variants. Since caliper body is the same, and you only need to change the caliper bracket. The following part numbers are what youâll need.
ANY TRW caliper body (again, part numbers vary due to it being colored, but they are otherwise the same exact caliper). These can be found on all 5,6,7,8 and SUV G series models.
The stock brake system is very capable, even though the z4 weighs in a couple hundred pounds more to the supra. During corner balancing, my car weighs in at ~3750lbs. I use the 374mm front rotors with EBC yellow pads which I find to be the perfect upgrade that performs well on the street and track.
Front brakes:
To begin, the front M âsportâ brakes come in 3 different sizes depending on the chassis. The brake calipers are stamped in the back that indicate piston count and size, and what size rotor it will fit on. For example, the stock brakes are labeled â4x40-44/348/36â and all variants are made by Brembo. The mounting holes measure 14mm apart center to center, and all interchangeably mount on the wheel hub (aka swivel bearing in BMW terms)
â4xâ= 4 pistons
40-44= one piston is sized 40, the second piston is 44 (in mm?).
348/36= the rotor size it is compatible with (348mm diameter, 36mm thickness)
40-44= one piston is sized 40, the second piston is 44 (in mm?).
348/36= the rotor size it is compatible with (348mm diameter, 36mm thickness)
BMWâs marketing lingo: M sport vs M performance. I hate how much BMW has diluted the use of M branding. If youâre like me, you didnât realize there is a difference between âsportâ and âperformanceâ. These are not interchangeable terms without context. What is âperformanceâ for one chassis, is âsportâ for another. For example, the âM Performanceâ brake for the g20 3 series upgrades the front brakes to 374x36 rotors, but keeps the same exact rear brake caliper size as the âm sportâ on the g20 cars. They just get painted red, come with dimpled rotors, and cost about 3k for the package. To make things more confusing is that these brakes are equivalent to the âM Sportâ of the 5 series g30!
The âM performanceâ package for the g30, which upgrades the brakes to 395x36 rotors, is the same brakes on the âM sportâ on the x5 g05 and x7 g07 SUVâs!
One thing to consider is that âM Performanceâ brakes are a dealer addon whereas âM Sportâ is a factory configuration (S2NHA). Also note that US and euro models will have slightly different offerings, so this will mostly focus on US models.
Part numbers can vary for components that are technically the same. For example the brake caliper on G20 M performance brake package is painted âredâ and is EXACTLY the same as the g30 M Sport but itâs painted blue- thus a different part number. The cost of the G20 m performance package is $$$ more compared to sourcing g30 m sport calipers.
Please consider that part numbers have been updated throughout time. There may be other newer/older part numbers that should be interchangeable.
The master cylinder is the same on all 3 series models for US Spec only. The z4 shares the same master cylinder as the 3 series, which I assume is the same for the supra. The brake servo/booster is bespoke to the z4/supra only. Since piston sizes are the same regardless of the caliper size, brake pedal feel should virtually be the same. If you live outside of the US, the master cylinder will need to be upgraded and BMW calls for it to be coded as well.
348x36
- Caliper PN 34116891273 (L) 34116891274 (R)
- Rotor PN 34116860911 (L) 34116860912 (R)
- Found on G20 m sport package, g30 m sport package (not 540i or m550i), x3 g01 m sport package (euro only, not m40i)
- Caliper PN 34116891303 (L) 34116891304 (R)
- Rotor PN 34116875283 (L) 34106875284 (R)
- G20 M performance retrofit kit PN 34112450468 (increased front size, same rear size, painted red, dimpled rotors)
- Found on g20 m performance package, g30 m sport (540 and m550i), g11 7 series and g12 8 series (not m850i) m sport, and x5 standard gray brakes.
- Caliper PN 34106891327, 34106891319 (L) 34106891328, 34106891320 (R)
- Rotor PN 34116887397 (L) 34106887398 (R)
- G30/G11/G12 M performance retrofit kit PN 34112289348 (increased front size, same rear size, painted red, dimpled rotors)
- Found on m850, 7 series LCI, x5 and x7 M sport. There are different part numbers for the cars vs the SUVâs, but I believe these should all fit regardless.
Rear brakes:
The rears are a little tricky. Factory M sport brakes for the z4/supra/g20 use a 345mmx24 rotor. The caliper is manufactured by Mando. For most other chassis models, they will also use a 345x24 rotor, but use TRW as the manufacturer. Piston size is exactly the same. While these are MOSTLY interchangeable, there are two key differences.
The TRW caliper body can accommodate both a 345x24 AND a 370x24 rotor. The only change is the caliper carrier bracket to accommodate larger pads and rotors. While the piston sizes are the same between the Mando and TRW caliper, the Mando caliper ONLY fits a 345mm rotor and cannot simply benefit from a caliper bracket change like the TRWâs can. Having specâed with Mando calipers, you will need to upgrade to any TRW caliper body, but with caliper carrier brackets specâed for 370mm rotors.
Additionally, the ebrake motors are physically different. While the mounting holes for the motor onto the caliper body are the same, the mating surface is completely different. The motors themselves cannot be swapped between a Mando and TRW caliper. This makes things a little tricky because the plug bodies are keyed differently. The supra/z4 uses a blue male plug, and TRW caliper will use a white male plug. The outer plug housing is the same âDâ shape. Fortunately, they are pinned exactly the same and labeled accordingly (male and female plug will be labeled with a â1â and â2â) In order to maintain the factory use of the ebrake, you will need to modify the female plug housing of the ebrake motor. This can be achieved by heating up a flat head screw driver, and âmeltingâ off the keyed slots of the female plug housing in the ebrake motor. Even after modifying the ebrake housing, the plugs will still clip into eachother so there is no issue with the plug coming off.
see the black "slots" in the plug housing that need to be melted/grinded off.
Caliper carrier brackets measure 9mm between the center of the mounting holes.
Similar to the fronts, the rears are also stamped with sizes.
Supra/z4/g20: MANDO 330 BMW 44 345-24
Other models: TRW XXXXXX BMW 44/24 345-370
44 = piston size (mm?)
345-24= rotor size 345 diameter, 24 width.
345-370/24= interchangeable between 345 and 370mm rotor size, 24 width.
The other numbers are just part numbers, I believe. Google searching those other stamped numbers yields no results.
Other models: TRW XXXXXX BMW 44/24 345-370
44 = piston size (mm?)
345-24= rotor size 345 diameter, 24 width.
345-370/24= interchangeable between 345 and 370mm rotor size, 24 width.
The other numbers are just part numbers, I believe. Google searching those other stamped numbers yields no results.
The TRW calipers come in unpainted, blue, and red variants. Since caliper body is the same, and you only need to change the caliper bracket. The following part numbers are what youâll need.
ANY TRW caliper body (again, part numbers vary due to it being colored, but they are otherwise the same exact caliper). These can be found on all 5,6,7,8 and SUV G series models.
- 370mm carrier bracket unpainted 34206871661, blue 34206883005 (L) unpainted 34206871662, blue 34206883006 (R)
- 370x24 rotor 34206896673 (L) 34206896674 (R)
- Vehicles specâed with the 370mm rear rotor from factory are g30 msport LCI models (2020 and later), g10/g11, x5/6/7.
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