[F87source]

Credit: 034Motorsport https://www.034motorsport.com/2-piec...-m2-m3-m4.html



Credit: 034Motorsport https://www.034motorsport.com/2-piec...-m2-m3-m4.html



Introduction:

Warning: This will be a really long and indepth review, I will try my best to go over every aspect of aftermarket rotors and these 034Motorsport rotors in as much detail as I possibly can (wherever necessary). My goal with this review is to try and give you as much information as possible regarding brake rotor upgrades and the 034Motorsport rotors in particular - because I know that upgraded rotors are not cheap and that makes pre-purchase research that extra bit more critical so you don’t end up wasting your money. So if you understand a particular section discussing background knowledge feel free to skip it.


In this product review I will be going over the general details of brake rotors (types of internal vanes, types of external features - slotting, drilled holes, J-hooks/J-slots, and what floating rotors are). Then I will take an indepth look at the 034Motorsport front and rear brake rotors for and offer my justifications on why I think 034Motorsport offers the best overall package for brake rotor upgrades on the F8x (m2, m3, m4) platform. This is also quite a feat, because rotor technology has been around for a VERY VERY long time, and that technology has been seen by everyone and therefore these designs have had time to be copied and improved on and so on and so forth. So in essence rotor technology has matured to the point where the differences between these rotors are so minute, that it takes a culmination of wins to be the overall best. Make no mistake, despite there being very fine margins between the competition (there is only so many ways you can make a round metal brake disk) - there are small differences you can make to set yourself apart from the competition and I believe 034Motorsport has made said differences.



So if you’d like to buy these rotors here are some links to do so (note: these rotors will only fit the F8x cars with the 4 pot front and 2 pot rear blue M brakes):

Front rotors:

Option 1:
https://www.034motorsport.com/2-piec...-m2-m3-m4.html

Option 2:
https://www.fcpeuro.com/products/bmw...t-034-301-1009

Option 3:
https://www.turnermotorsport.com/p-6...-kit-380x30mm/


Rear rotors:

Option 1: https://www.034motorsport.com/2-piec...-m2-m3-m4.html

Option 2:
https://www.fcpeuro.com/products/bmw...t-034-301-2009

Option 3:
https://www.turnermotorsport.com/p-6...-kit-370x24mm/


I would highly suggest purchasing them from option 2 (FCP Euro) or option 3 (Turner motorsport/ECS Tuning) because these 2 vendors have lifetime replacement guarantees - meaning if your rotors wear out from heavy track or street use, you can get a new set replaced for “free” (depending on the replacement policy they may refund you your original purchase price as credit, and this credit might be more or less than the current price of the rotors depending on current prices aka inflation or if your rotors were originally purchased on sale).



Disclaimer:

Damage/Injury Disclaimer: Any information, guidance, technical advice, coding advice, tuning advice, datalogging advice, installation instruction, calculation, experiment, safety information, or product installation demonstrated in my reviews is to be consumed and or done at your own risk. I will not be responsible for personal injuries, injuries to others or any living being, or any damage to your car, or any property damage.

Monetary disclaimer: I do not make commission, or profits or any kind of monetary gain from the sale of the 034Motorsport front for rear 2 piece brake rotors for the F8X Bmw cars.

Sponsorship disclaimer: The way my reviews work is that I determine what product that I want to buy and actually use on my own car, and during this process the product that I end up choosing is what I believe is the best option on the market. I then reach out to the company offering the product and ask them if they would be willing to sponsor me in a review, if the answer is yes then I write a review, if the answer is no I would end up buying the product (sometimes at a later date) but I wouldn’t complete a detailed review about it (I might write something, but not to the same extent as my standard reviews). But the critical thing is that I reach out for a sponsorship and not the other way around, this means that the products I am reviewing are actually things I believe in and would use on my own car. This also means that I am not being paid to review something I do not care about. Would I do a review if a sponsor reached out to me? The answer would depend on if I believed in the product, and I would make it clear in my review if this were the case. But at the time of writing this review, such an interaction has not occurred yet.


Time of writing disclaimer: everything I am writing about in this review is described at the time of writing and may not be updated in the future, so there is a potential that things are no longer accurate in my comparisons as parts are changed and upgraded as time passes.


Bias and comparison disclaimer: Throughout this review I will attempt to be as unbiased as possible while drawing comparisons to other products.


Mistakes and Inaccuracies Disclaimer: Throughout my review I will try to be as factually accurate as possible, but there are always chances that I make mistakes and write things that are incorrect/false. If this is the case please point it out to me and if indeed it is true that I am incorrect, I will correct these mistakes and apologize for them. Afterall I am only human, so mistakes can and will inevitably happen.


Subjective Disclaimer: Please note, these reviews are also written in my own opinion, so when I am comparing different products to determine what I see as the best, there are many factors that I go through to form this opinion. Obviously there will be disagreements between people, so I will do my best to objectively determine what I deem to be the best, but at the end of the day it is still just my own opinion whether it be right or wrong. Take whatever I say in my reviews with a grain of salt.


Information Disclaimer: I read a lot of material over the years just out of sheer interest or to make these reviews. I also accumulated a lot of knowledge over my many years of education that are really relevant to cars (Physics, Chemistry, and Mathematics). That being said, my reviews are mostly based on this accumulated knowledge and I cannot always cite these sources due to the original source material possibly being lost to time, or there being so much knowledge compiled to make a single point. So, when possible I will cite my source(s) (for example data on tensile strength of a metal, or peer reviewed research). There are cases when I get information from blog posts, youtube videos, or forum posts I may not cite it, because I go through a lot of these sources only to use the gained knowledge in a small section of my review and it is not feasible to list them all. So pretty much what I am trying to say is I am not citing “common knowledge” - I will cite peer reviewed research and photos though, or really explicit user experiences.



Image Credits:

Images and videos used in this review are all property of their rightful owners as credited below each image, I am just using them for the purpose of this review but if you (the owner of the image) would like them removed please let me know via pm. Otherwise thanks to the respective image owners (I made sure to credit your online name and link where I found the photo) of the photos, without you this review would be so much more bland.



Review Disclaimer:

First and foremost I would like to thank 034Motorsport and Sean over ar 034Motorsport for agreeing to sponsor me for this review. Despite this I will remain as unbiased as possible during the review. Please note, the dynamics of this relationship was that I reached out for a sponsorship review and not the other way around. This should demonstrate how I truly feel about these rotors - in the sense that I truly believe it is an excellent product and one of the best offerings on the market. In fact I actually have these front and rear rotors installed on my own m2 as of now, and I really love their looks, their ability to clear pad build up, and I am certain I will love their ability to float and vent extra air when I take the car to the track.

An additional note for full transparency sake (I don’t like to hide anything, because I am not a shill, and I want to make this point very clear) is that I did also talk to both Paragon and EBC rotors in regards to a sponsorship and talks did commence quite far with Paragon to the point that I was actually given a deal to review the Paragon Rotors. However, in the end I chose the 034Motorsport rotors over the other 2, the reason being I felt the 034 rotors had slightly better technology (again we will discuss this in the review), and the overall sponsorship deal was better (no offense to Paragon or EBC, they make good stuff that I would gladly run on my car, but 034 is that tiny bit better so I went with 034). So pretty much what it came down to was 3 options to choose from, and the best choice was clearly 034 because imo they had the overall better rotor technology plus a better sponsorship deal that is a rare win win for me (because 99% of the time the better thing would cost me extra). But let me clarify that the sponsorship deal isn’t the only deciding factor, because I would happily pay a bit extra out of my own pocket to get a better product. So if I had a chance to redo this decision and all 3 sponsorship terms were equal I would still pick the 034Motorsport rotors. That should say everything that needs to be said. It’s not just about the better deal, it is about the technology too, because you could offer me free stuff all day long, but if it is not something I believe in then I still won’t take it, because I don’t put garbage on my car - hence why these were the only 3 companies I reached out to.



Parts of a Brake Rotor:

Let’s begin this review by quickly going over the parts of a brake rotor:


Credit: Viper Parts of America https://www.viperpartsrackamerica.co...rotor-04815750


So in the image above we have a drawing of a basic brake rotor. The outer disk where the brake pads clamp down on and provide the stopping force is known as the friction ring. The inner part which connects the friction ring to the hub is known as the rotor hat or the bell. These are the 2 basic parts of a brake rotor.



Intro into Brake Rotor Venting:

Next we will be going over brake rotor venting and what this is. We all know that as we brake, the friction of the brake pads against the rotors generate heat in both the pads and the brake rotors themselves. The amount of heat generated will depend on what kind of braking is done and what kind of car we are talking about. For instance on a really small lightweight passenger car like the Smart ForTwo Smart car, the brakes will see relatively low amounts of heat as the car is really small and lightweight and doesn’t typically see a lot of repetitive back to back braking from high speed to near standstill conditions. Whereas on a high performance BMW M car like the m2, m3, and m4 which are fairly heavy at 3400 lbs+ and potentially see a lot of track use with plenty of high speed braking, these brake rotors get very very hot. If these rotors get past a certain thermal threshold they will begin to over heat, and this will cause brake fade as the rotor temps greatly influence brake pad temps which can cause pad fade. The rotors can even glaze over which may permanently damage them (depending on what rotors you have and how much thickness you have left you may be able to repair them by machining the rotors) and require replacement.


To reduce this overheating issue manufactures have 2 rotor construction types, solid rotors and vented rotors:


Credit: Summit Racing https://help.summitracing.com/app/an...ented-rotor%3F


- The solid rotors are lighter weight, easier to manufacture and cheaper overall. These rotors are typically used on those lighter weight cars that don’t see extremely high braking temperatures, or they are used solely on the rear axle of cars - since the rear brakes do less of the braking due to brake bias and weight transfer under braking.

- The vented rotors are heavier since they require more material (essentially are 2 solid rotors sandwiched together with vanes in between), are more complex to make, and cost a lot more. The benefit of vented brake rotors is that it allows air to be sucked through the inside of the brake rotor cooling down the inner and outer rotor faces itself, and this greatly reduces the chances of rotor overheating.


So in summary brake rotor venting is the process of introducing vanes in the middle of the rotor itself to allow for airflow to keep the rotors cool. We will go more in depth into how this works and also talk about rotor vane designs in the next section.



Brake Rotor Vane Designs:

Next let's talk about the design of these internal rotor vanes, because there are a lot of different designs and they make massive impacts on how air flows through the rotor and how effective they are at cooling the rotor face down.


Credit: Rick’s Free Auto Repair Advice https://ricksfreeautorepairadvice.co...-vane-designs/


So in the image above we have some of the various rotor vane designs:

1) Straight vane configuration: In the leftmost design, we have a straight vane configuration these are the simplest to make and are the cheapest to produce, but the cons are that this vane layout doesn’t flow much air, as the straight vane configuration doesn’t allow the vanes to act like fan blades to pump air out of the rotor. However, the benefits of having perfectly straight or radial vanes is that they are not directional, they can work on either side of the car without issue.

2) Curved Vane Design: In the second image we have a curved vane design, these curved vanes are more complex and expensive to produce. But the pros of this design is that the vanes act like a radial flow fan, and this causes the vanes to create pressure and suction sides allowing for air to be actively pumped from the center of the rotor out to the edges. This design can potentially flow a significant amount of air and can offer the greatest amount of rotor cooling. However, the negatives of this design is that they are directional so if you put the rotor on the wrong side of the car the vanes will not be able to pump air optimally (it will try to suck air from the edges and vent it in the middle) and will operate extremely poorly. The vane design also has to be carefully modeled to maximize air flow, you cannot just throw some curves and hope it will pump air, fan blades like on turbos take a massive amount of refinement on CFD to optimize their flow, prevent flow separation, etc and the same will apply to brake rotors. So this is a costly endeavor to do right.


Here is diagrams showing more information of a curved centrifugal or radial flow fan:


Credit: rs Designs Park https://www.rs-online.com/designspar...entrifugal-fan


And if you are interested here is a research paper analyzing flow through a vented automotive brake rotor: https://citeseerx.ist.psu.edu/docume...860f156cb4ee6c


Note: Curved vane designs can be even more complex than this drawing, they can have split elements, converging or diverging designs, etc all in an effort to manipulate air flow. But I will just be going over the basics because there are just too many proprietary designs out there to go over them all.

3) Pillar vanes: The last design utilizes a pillar vane configuration, these are the most complex to produce and are also very expensive to make - both in manufacturing and in CFD designing. They are supposed to offer the same amount of air flow as curved vanes but not be directional. However this design isn’t as common on aftermarket rotors as curved vanes.

Next let’s address vane count. So we now know that the introduction of vanes into the rotor allows for ventilation to occur (via allowing air flow through the inside of the rotor), but vanes do much more than that. Vanes also add thermal mass to the rotor, and this allows the rotor to absorb more thermal energy before increasing in temperature. Vanes also act as heat exchangers to help pull heat from the rotor faces, and then help dissipate said heat amongst the entirety of the vane thereby also increasing surface area. So vanes increase thermal mass, act as heat exchangers, and increase surface area for thermal dissipation. So vane counts are really important then, because the more vanes you have the more of these benefits you gain - however at some point there will be diminishing returns. Because if you have too many vanes the rotor eventually becomes a solid rotor again or it can’t flow enough air because the gaps between the vanes are too small.


In general the aftermarket brake rotors for our BMW F8X platform come in 48 or 72 vane configurations, with a vast majority of the offerings being 48 vane counts likely because they are cheaper to make. These rotors can also vary in vane layout, with there being standard individual vanes stacked side by side, or there can be layouts where every other vane is splits into many smaller segments to increase surface area and manipulate air flow, there can also be variable vanes where there are multiple rows of vanes with inner and outer rows and each row potentially having different vane counts. This all depends on the manufacturer, and is done in an effort to have the best air flow possible.


For example below, this is how Brembo lays out their rotor vanes:


Credit: Speed Academy http://speed.academy/rotor-one-two-p...ds-and-budget/



In summary rotor vane configuration, and count are incredibly complex with a lot of time and energy spent developing a pattern that will allow the most amount of ventilation and heat exchange as possible. But a really rough general rule of thumb is that curved vanes are better than straight vanes (if optimized properly otherwise it won’t be any better) for cooling, and a high vane counter is better than a low vane count. I won’t really discuss pillar vanes too too much, because they are kind of rare in aftermarket rotors (I believe the only companies that use this technology extensively are Brembo and DBA).


Note: Vane thickness also plays a factor in air flow, thermal mass, and thermal transfer - but these are all really subjective things that each manufacturer does differently from one another, and so I won’t discuss it too much as I won’t have the data to make any meaningful analysis.



Rotor Face Design:

Now that we know about the inside of the rotors, let’s talk about the outside of the rotor - in particular the face of the friction rings. So why would we even have different styles of friction ring faces? Why can’t it just be a smooth faced rotor? Well the answer to that question is to help stop brake fade. Because as brake pads get hotter and hotter on the track, at some temperature threshold the friction material will begin to off gas. This released gas will then form a gaseous film between the friction ring face and the brake pad, and this drastically reduces the friction available and causes brake fade. So if we alter the design of the friction ring face, we can help push away and vent this gas thereby preventing brake fade due to off gassing pads. This new design will also help prevent rain water from decreasing brake friction as well. Different rotor faces can also help scrape the brake pad clean, preventing uneven deposits from forming which causes brake juddering.


So let’s talk about these rotor face designs:

1) Plain smooth friction rings:


Credit: ECS Tuning https://www.ecstuning.com/b-zimmerma...4116792223zkt/


These are the most basic type of rotor face with nothing on the face of the friction ring.

Pros:
- Very low pad wear: There are no ridges or holes on these friction rings to increase brake pad wear, so these types of rotors offer the least amount of wear.
- Low NVH: With a smooth face, these friction rings do not generate any additional noise, vibration or harshness - so these types of rotor faces offer the lowest NVH.
- Even heat distribution: an even friction ring face allows for heat to be uniformly distributed so there are no weird hot spots.

Cons:
- Brake Fade: These rotors are susceptible to brake fade due to pad off gassing as there is no effective way to vent that gaseous film between the friction ring and the brake pads. So these rotors are more suited for street usage.


2) Drilled friction rings:


Credit: Turner Motorsport https://www.turnermotorsport.com/p-3...e-rotors-pair/


These are the types of rotors you normally find on sports cars such as the BMW f8x m2, m3, m4, Nissan Gtr, Porsche GT3 RS, etc. These rotors are more aesthetically pleasing than the plain faced rotors, and are the first step into properly dealing with brake pad off gassing.


Pros:
- Increased “brake bite”: due to the increase in edges amongst the rotor face from the drilled holes, the pads have more places to bite onto increasing braking power.
- Reduced brake fade: the holes allow for the friction ring surface to be ventilated and this prevents brake pad off gassing from reducing brake friction. This drastically reduces brake pad induced fade.
- Pad cleaning: The holes and the increase in edges that they bring scrape against the pad surface cleaning them up. This ensures the brake pad friction compound is almost always clean and smooth, and this results in a better brake pad to friction ring face contact allowing for better braking.
- Even heat distribution: generally holes are very uniformly distributed and very abundant on the friction ring so heat distribution is generally good. However it will not be as uniform as the plain faced friction rings, with hot spots still forming around the hole and cooler spots forming between the holes. This might enhance cracking over time and cause pad deposits to build up. So this is kind of a pro/con.

Cons:

- Cracking: Holes are more proned to cracking than slots or a plained face rotor - because you removed all the supporting material there. This makes drilled rotors unsuitable for track use, because they are proned to cracking, and if cracks join up they can cause the rotor to completely fail.
- Increase pad wear: the negative side to having more edges on the friction ring face is that it causes more wear when the pads scrape up against them. Technically drilled rotors are supposed to be the worst in pad wear because there are so many more holes compared to slots, but this might vary.
- Increase in noise: the increased number of edges that comes along with drilled holes that allows enhanced brake pad biting and cleaning results in more noise due to these edges scraping the pad as they rotate by. This means drilled rotors increase NVH over smooth faced friction rings during driving. Again these are supposed to be the loudest style of rotor because of the number of edges they have over slotted rotors.


3) Slotted friction rings:


Credit: Turner Motorsport https://www.turnermotorsport.com/p-1...-380x30mm-f8x/

Slotted rotors are the common upgrade path for those who are moving on from their factory rotors and want something more capable of track abuse without cracking. Most aftermarket slotted rotors have straight slots that go diagonally from the hat towards the edge of the friction ring. However the critical thing to note is that the slot must not touch the edge of the friction ring or the hat as this can enhance cracking. Slot patterns are not limited to just straight slots, you can see there are a bunch of crazy patterns out there like zig zags etc.


Pros:

- Increased “brake bite”: due to the increase in edges amongst the rotor face from the slots, the pads have more places to bite onto increasing braking power. However, slots have less edges than the drilled rotors so they offer less pad bite.
- Reduced brake fade: the slots allow for the friction ring surface to be ventilated and this prevents brake pad off gassing from reducing brake friction. This drastically reduces brake pad induced fade.
- Pad cleaning: The slots and the increase in edges that they bring scrape against the pad surface cleaning them up. This ensures the brake pad friction compound is almost always clean and smooth, and this results in a better brake pad to friction ring face contact allowing for better braking.


Cons:

- Increase in pad wear: the increased edges which allow for better brake bite also comes with the cost of more rapidly wearing down pads. Slotted rotors technically should be behind drilled rotors for brake wear.
- Increase NVH: again the increased edges will increase noises as well.
- Hot spotting: Slots tend to create hot spots on the friction ring face, because the slots themselves get hotter due to the increased friction due to the edges allowing for better pad biting, and the surrounding areas are cooler. This hot spotting can potentially result in cracks and maybe even pad deposits.


4) J-Hook’s or J-Slotted friction rings:


Credit: 034Motorsport https://www.034motorsport.com/2-piec...-m2-m3-m4.html


J-hook rotors or J-slot rotors are in my opinion the best type of friction ring design, they were iirc pioneered by AP racing (who imo are the pinnacle of brake technology, and are second to none - they are the best of the best full stop) and now are being adopted by other brands like 034Motorsport who call them J-slots.


Pros:

- Increased “brake bite”: due to the increase in edges amongst the rotor face from the J-slots/J-hooks, the pads have more places to bite onto increasing braking power. J-hooks/J-slots are more present on the rotor than traditional slotted rotors so they have more edges. This increases brake pad bite over slotted rotors but still fall behind drilled rotors.
- Reduced brake fade: the j-slots/hooks allow for the friction ring surface to be ventilated and this prevents brake pad off gassing from reducing brake friction. This drastically reduces brake pad induced fade.
- Pad cleaning: The j-slots/j-hooks and the increase in edges that they bring scrape against the pad surface cleaning them up. This ensures the brake pad friction compound is almost always clean and smooth, and this results in a better brake pad to friction ring face contact allowing for better braking.
- Even heat distribution: The J-hooks/J-slots offer better heat distribution than standard straight slots because the hooks are more abundant on the rotor, and are curved to spread heat around a larger area. They still fall behind the plain faced rotor and the drilled rotor in heat distribution. This means the slots will be hotter than the surrounding friction ring meaning it can lead to cracking and hot spots. Again this is a pro/con but since it isn’t as bad as slots I will leave it as a pro.


Cons:

- Increase in pad wear: the increased edges which allow for better brake bite also comes with the cost of more rapidly wearing down pads. J-hook/J-slot rotors technically should be behind drilled rotors for brake wear but ahead of slotted rotors.
- Increase NVH: again the increased edges will increase noises as well. I have heard J-hook/J-slot rotors are the worst offenders for NVH increase as they have more edges than a straight slotted rotor, and the hook shape causes a weird buzzing sound. But this depends on your car’s sound insulation, the pad material you are using etc.


5) Anything else: There are limitless possibility for friction ring designs, and they could range from a combination of any of the above (thereby gaining a combination of the strengths and weaknesses of each of these designs) or to something extreme like zig zags, squiggles, etc.



Brake Rotor Expansion :

Before I talk about the different types of rotors on the market I would like to quickly go over brake rotor expansion. When a brake rotor gets extremely hot (and this will happen even with well ventilated rotors - it’ll just take longer) it will begin to expand in a radial and axial direction. This is due to the fact that metal expands when it gets hot, and this still applies to brake rotors.

If you refer to the image below, you will see radial expansion is expansion parallel to the face of the rotor. Axial expansion is expansion perpendicular to the face of the rotor (in the direction of the axles).


Credit: Loren K https://www.quora.com/What-is-radial...tial-and-axial


So in essence, radial expansion is when the rotor diameter increases and axial expansion is when the rotor thickness increases.



Floating 2 Piece Rotors vs. Everything Else:

Now let’s discuss the types of brake rotors available on the market:


1) Solid 1 Piece Rotor: A solid 1 piece rotor is a style of brake rotor where the hat and the friction ring are one single piece - usually formed out of cast iron. An example of this is the stock BMW m235i rotors:


Credit: ECS Tuning https://www.ecstuning.com/b-zimmerma...4116792223zkt/



Pros:
- The rotors are extremely cheap to make as they are primarily just cast from a mold.

Cons:
- Heavy: Since the hat is cast iron.
- Thermal Conductivity: It more easily conducts heat to the wheel hubs and wheel bearings due to its single piece design. This extra heat more rapidly wears out components.
- Poor ventilation: The single piece design doesn’t allow air flow from the front of the rotor to the inside of the bell, this limits air flow for rotor ventilation.
- Warping: The single piece rotors are extremely susceptible to warping because the friction ring is not able to freely expand radially or axially as it is solidly attached to the hub at the outer rotor face. This means as the friction ring expands it is held down on one side (the outer side) but not the other side (back side) and the rotor begins to warp easier in one direction vs. the other, and the rotor “cups” like a pepperoni slice. This warping causes horrible brake juddering and vibrations, and pretty much renders the brake rotor garbage and requires a replacement.


Introduction to the 2 Piece Rotors:

To solve this warping issue rotors were split into 2 separate pieces, the friction ring and the hat. The hat and the friction ring were then attached together with a type of pin, and depending on this pin - radial and or axial expansion could be achieved. 2 Piece rotors also often utilized aluminum hats to reduce brake rotor weight over the heavy cast iron hats of 1 piece rotors. 2 Piece rotors also offered gaps in between the hat and the friction ring which offered 2 main benefits: Improved ventilation and reduced thermal conductivity, this resulted in better rotor cooling and reduced thermal conductivity into the wheel hub and the bearings.


2) Semi-Floating Rotors: Semi floating rotors are rotors that allow the friction ring to “float” or expand in the axial or radial direction (only one of the two but not both) without resistance. This means the friction ring will be able to resist warping when expanding in one of these directions. Generally speaking semi floating rotors are more commonly built to allow radial expansion rather than axial expansion.


Pros:
- Warp Resistance: Resistance to warping is achieved in the direction the rotor allows float in (axial or radial).
- Lighter weight: Since the hats in 2 piece rotors are typically made of aluminum, the overall rotor weight is drastically reduced over solid 1 piece cast iron rotors.
- Reduced Thermal Conductivity: These 2 piece rotors typically conduct less heat into the wheel hubs and bearings due to the aluminum hat having multiple smaller surface area contacts to the iron friction ring.
- Improved ventilation: The way the hat is attached to the friction ring allows for improved air flow into the bell from the front and from the back. This is because there are gaps in the front of the rotor now between the friction ring and the hat allowing for more flow into the bell. The hat also usually mounts in a way where none of the vanes will be restricted from air flow as well.


Cons:
- Increased Price: The 2 piece rotors will cost more to manufacture since it no longer is a simple casting procedure (the aluminum hat needs to be machined out of a block of aluminum and then anodized, and the pin mechanism to allow for floating isn’t cheap to make either. The final product will also need to be hand assembled and torqued to spec adding additional labor costs.
- Warping: Semi-floating rotors are still susceptible to warping in direction that the rotor doesn’t allow expansion in.
- Not truly 2 piece: although the hat and friction rings are 2 different materials, typically the pin system doesn’t actually allow you to remove the friction ring from the hat. So technically they are not truly 2 pieces - well not all the time at least.



3) Fully floating rotors: These rotors are the crown jewel in preventing friction ring warping under extremely high temperatures, because they allow the friction ring to expand both radially and axially. How do they accomplish this? Via the use of bobbins (pretty much a fancy nut and bolt assembly to put it as basic as possible) that are slightly longer than needed to secure the hat tightly to the friction ring (aka it doesn’t clamp the rotor to the hat super tightly, it more so prevents the friction ring from being separate from the hat) allowing the friction ring to have room to expand axially if needed. The holes on the hat where these bobbins thread through are also typically a bit larger than needed as well to allow the friction ring to expand radially if needed as well. So pretty much there is a bit more tolerance in the mounting system.


Pros:
- Warp Resistance: Resistance to warping is achieved in both the axial and radial directions.
- Lighter weight: Since the hats in 2 piece rotors are typically made of aluminum, the overall rotor weight is drastically reduced over solid 1 piece cast iron rotors.
- Reduced Thermal Conductivity: These 2 piece rotors typically conduct less heat into the wheel hubs and bearings due to the aluminum hat having multiple smaller surface area contacts to the iron friction ring.
- Improved ventilation: The way the hat is attached to the friction ring allows for improved air flow into the bell from the front and from the back. This is because there are gaps in the front of the rotor now between the friction ring and the hat allowing for more flow into the bell. The hat also usually mounts in a way where none of the vanes will be restricted from air flow as well.
- Replaceable friction ring: the complete floating design usually means that the pins attaching the friction ring to the hat may be removed. This allows the friction ring to be replaced independently of the hat.


Cons:
- Increased Price: The 2 piece rotors will cost more to manufacture since it no longer is a simple casting procedure (the aluminum hat needs to be machined out of a block of aluminum and then anodized, and the pin mechanism to allow for floating isn’t cheap to make either. The final product will also need to be hand assembled and torqued to spec adding additional labor costs.
- Noise: floating rotors typically are very loud compared to semi-floating rotors and solid 1 piece rotors, this is because if you want to allow the friction ring to be able to move axially and radially there must be play in the mounting system. This means the friction ring can rattle around a bit in relation to the hat because it technically isn’t firmly attached. To solve this some rotors come with anti-rattle clips that add some tension to the pins attaching the friction ring to the hat, and this “pinches” the friction ring to the hat ever so slightly to keep it firmly held in place. However, when enough heat is put into the friction ring that it needs to expand the anti-rattle clips give way and compress back (like a spring) to allow for the friction ring to expand in whatever direction it needs to. For example if it needs to expand radially the anti-rattle clips don’t exert enough clamping force to stop that, if it needs to expand axially again the friction ring’s expansion can push the clips back because there isn’t that much tension there that it can stop the expansion.

Here are some images of this anti-rattle clip system:


Credit: F87Source


Credit: F87Source



But if you are still confused about all of this, this video is ok at explaining the fully floating 2 piece rotors. You can also see the play in the rotors, how the hat mounts to the friction ring, the bobbin system, etc: https://www.youtube.com/watch?app=desktop&v=U0IULtZ1qEk



Stock F8X Blue M Brake Rotor Analysis:

Now that we know a little bit about brake rotors (well at least enough to have a decent high-level discussion on aftermarket rotors) let’s first take a look at the stock rotors that come on the F8X M cars - because they are actually pretty decent.



Credit: F87Source


Credit: F87Source


So the stock BMW F8X Steel rotors, well like I alluded to, are pretty good - BMW actually took the time and effort to develop brake rotors that are unbelievably good for OEM standards and even good for aftermarket standards. Literally some OEMS would be jealous to have these rotors as stock - and I am talking about Audi who kind of skimped pretty hard on their rotors from what I have seen.

Now what am I talking about exactly? Well BMW implemented a drilled 2 piece semi-floating in the radial direction steel brake rotors with directionally curved vanes on these F8X cars. Yeah that’s a mouth full, but this leads to some excellent performance from these rotors, and let’s expand on these pro’s:

1) These rotors are 2 piece, meaning the hat is actually aluminum and the friction ring remains iron. This is incredible to see from OEM’s because it saves a tremendous amount of weight from the brake rotors, and even with aftermarket rotors you would be hard pressed to save more than 1 lb or so. So this is an incredible feat by BMW, and something any OEM would appreciate to see.

2) These stock rotors are semi-floating in the radial direction which is an excellent benefit compared to 1 piece fixed rotors, as it helps prevent warping. This was done by having fixed pins attach the friction ring to the hat:


Credit: Jason via BMW M https://f80.bimmerpost.com/forums/sh...d.php?t=971411


3) These rotors have directionally curved vanes with ventilation also permitted through the hat since they are 2-piece rotors and have gaps in the hat. This means the stock rotors are able to pump air through the curved vanes from the center of the hat to the outer edges of the friction ring and enhance cooling. BMW actually also did a really good job with the vanes on these stock rotors, because they are truly directional, meaning the left side and right side rotors have vanes that are shaped for their specific direction of rotation. This is something that not alot of manufactures actually do, because it requires 2 different part numbers - I believe Audi is one of the manufacturers that only make directionally ventilated rotors for only one direction and use them on both sides, meaning one of the sides will have vanes going in the wrong direction which doesn’t allow the rotor to pump air effectively.

4) The stock rotors have a drilled face, this allows the rotors to have more biting surfaces to enable better pad bite while also dealing with pad off gassing.


Now let’s talk about the Con’s:

1) Drilled design: The drilled design is extremely susceptible to cracking when subjected to very high temps - specifically on track.

2) Semi Floating: The semi-floating design in the radial direction still prevents the friction rings from expanding in the axial direction, so the rotors are still susceptible to warping this way.

3) Low Vane count: The stock rotors have approximately 36 directionally curved vanes (I couldn’t really tell if the vanes are segregated internally because I didn’t spend too much time examining the stock rotors), so the vane counts are quite low compared to aftermarket rotors. This limits cooling capability, surface area for heat exchange, and thermal mass of the rotors - so cooling will not be as good as a high vane count aftermarket rotor.

4) Non-replaceable friction ring: Unfortunately the friction rings are not removable and thus cannot be replaced by themselves, but the good news is that these rotors are super cheap so replacement isn’t a big deal.

5) Limited ventilation: Despite being a 2 piece rotor with gaps in the hat for additional ventilation into the bell region of the hat, the ventilation will be limited due to the semi-floating design requiring the pin be in the same region as the vanes. This takes up space in the bell region of the hat limiting air flow to the vanes.


So overall the stock F8X BMW rotors are an absolutely fantastic piece of kit by OEM standards, but we can do much much better - especially if you want to track your car and require as much brake cooling as possible.



034Motorsport Brake Rotors:

Finally, let’s go over the 034Motorsport Brake Rotors and the massive benefits you’ll find using these rotors over the stock ones, and why I personally think these are the best aftermarket rotors currently available on the market.



Unboxing:

Let’s begin with the unboxing experience so you know what you will be getting when you purchase a set of 034 motorsport brake rotors.

Rear Rotors:

- The 2 rear rotors come shipped together in a large outer box, and inside of that each rotor is individually packaged in smaller cardboard boxes with a foam tray holding the rotor. You also get a set of instructions inside of the box.


Credit: F87Source


Credit: F87Source


Credit: F87Source


Credit: F87Source


- Each rear rotor will have their associated parking brake hat zip tied to the main rotor hat. So before install cut the parking brake hat loose, install that first before installing the rotor.


Credit: F87Source



Front Rotors:

- Just like the rear rotors, the 2 front rotors come in a single large outer cardboard box, and they are stored in 2 separate smaller cardboard boxes with foam trays inside of the larger box. They also include their own set of instructions which are identical to the rear rotors, the only difference is that the front rotors don’t have parking brake hats.



Credit: F87Source


Credit: F87source




Instructions:

Here’s the rotor instructions for anyone who is curious and wants to see the information they contain, I’ll also post this so if you decide to throw your instructions away or lose them, there will always be a digital copy here just in case:


Credit: F87Source


Credit: F87Source


Credit: F87Source


Credit: F87Source



Front Rotor Images and Brief Analysis:
Now let’s look at the front rotors in more detail:

- In these first two images you can see the J-slots in the friction ring and how they overlap and essentially cover the entire span of the friction ring face - this will offer excellent pad cleaning and off gas ventilation. You also see the bobbin and the flat edge locking into the rotor hat. You’ll also notice that the hat is hard anodized in a sort of greenish bronze color.



Credit: F87Source


Credit: F87Source


- In the next few images you will see the side of the rotor hat and all the large gaps between the hat and the friction ring. This will enhance air flow into the bell region of the hat and therefore allow more cool air to be accessible to the vanes. The flow in this region to the inside of the bell due to suction from the vanes will also pull air across the friction ring face allowing for some extra cooling here too. Also the reduction of surface area in contact with the friction ring allows for reduced thermal conductivity to the hat and therefore the wheel hub and bearings. You will also see the directionally curved vanes of the front rotors, and the markings on the circumference of the rotor telling you the rotation direction (remember with directionally curved vanes you much have them installed with the arrow pointing in the direction rotation of the wheel leading to forward vehicle motion in order to get optimal air flow), production date, dimensions of the rotor, and minimum thickness the rotor can wear to before it must be replaced. You will also see that every second vane is split in half creating a slot to manipulate air flow and increase surface area. This is how the front rotor achieves 72 vane, because there are 48 vanes with every second one being split into 2 vanes resulting in 72 total vanes. This is also how brembo pictured some of their rotors achieving 72 vanes as well (refer to the image in the sections above), and this is a common technique as well to get 72 vanes without packing them too tightly, although that is another option. Some other manufacturers would also have varying vane configurations where the outside has more vanes than the inside all in an effort to manipulate air flow.


Credit: F87Source


Credit: F87Source


Credit: F87Source


- In the last few images you can see the back side of the front rotor and the back side of the hat. You will also see images showing the vanes from the inside of the hat, notice how tightly packed there are here compared to the outside circumference of the friction ring, this expansion towards the outside should create suction pulling air flow towards the outer edge just like a diffuser would on a car - so I suspect that is the benefit of going with a slotted second vane to achieve 72 vanes, because you get more space for expansion, personally I would prefer 72 individual vanes but just make them thinner - but there is more than one way to do things and this is the direction 034Motorsport went so there likely is a reason they did this, maybe they found they got better flow this way. You will also notice the other side of the bobbins, and the cap head screws securing them in place from the top, along with the anti-rattle clips and washers present to keep tension on the friction ring and prevent rattling despite the fully floating design. Also the way the bobbins mount the friction ring to the hat takes up much less space in the bell compared to the BMW pin solution for their semi-floating stock rotors, this allows much better flow to the vanes. However, one thing I would like to see changed is for 034 motorsport to reverse the bobbin design and put the anti-rattle clip on the other side of the rotor and reduce the hardware on the inside of the bell region even more. This will reduce disturbances and restriction of air flow going to the vanes even further.



Credit: F87Source


Credit: F87Source


Credit: F87Source


Credit: F87Source


So overall I am pretty impressed with their front rotors, it is an attractive design with very nice details to it (more on these details later). The only minor gripes I have is that I would prefer 72 individually curved vanes and have the anti-rattle clips on the front side to reduce interference to the air flow into the vanes. Also I noticed on my rotors that only one of the rotor set screw holes had the proper base plate that tapered the hole down to the correct size for the set screw to bottom out on instead of pass through the hole completely. This means the second set screw wouldn’t have anything to bottom down on and therefore couldn’t clamp the rotor to the wheel hub and therefore was useless. This isn’t a really big deal in my opinion, because the single set screw was enough to secure the rotor to the hub and these rotor set screws don’t serve any purpose except to hold the rotor in place when the wheel bolts are off. So there is no structural reason for their presence and not having them shouldn’t affect safety. It’s probably better that you have one less set screw because these things corrode so easily - my 14,000 km m2 that has never seen winter driving had the set screws seized to the hub (due to corrosion) so badly the hex almost rounded off when I tried to remove them.



Rear Rotor Images and Brief Analysis:

- So in the first 3 images you will see the front of the rotor, the J-slots, and the bobbins for the rear rotors. Just like on the front rotors, the rear rotors have a bronze colored hard anodized hat. You have the overlapping J-slots from the hat to the edge of the friction ring allowing for full brake pad scraping and off gas evacuation. You also see the back side of the bobbin.


Credit: F87Source


Credit: F87Source


Credit: F87Source


- In the next 2 images we see the hat of the rear rotor and where it attaches to the friction ring, notice the incredibly large gaps between the hat and the friction ring allowing for improved ventilation into the bell region of the rotor compared to the stock BMW rotors. We also see the vanes of the rotors themselves. The rear rotors utilize 36 directionally curved vanes with no slotting, and this is approximately the same vane count as the stock rotor (iirc, but I could be wrong). This does limit the amount of cooling from the rear rotors to a stock like level, however the increased amount of air flow from the large gaps in the hat to the bell region should allow for better cooling over stock.


Credit: F87Source


Credit: F87Source


- In the last 3 images you can see the back of the rear rotors, you can see the removable parking brake hat, the same bobbin system as the front rotors with the anti-rattle clips, and the internal vanes that also expand as they reach the outer edge of the rotors - again this should provide some suction. You also see the outer circumference of the rotors and the stamp showing the dimensions of the rotors, production date, minimum permitted thickness, and rotation direction.


Credit: F87Source


Credit: F87Source


Credit: F87Source



Rotor Indepth Analysis:

Now let’s analyze the 034Motorsport rotors a little bit closer, most of the topics discussed here will be a reflection of topics we have discussed earlier on in this review and essentially discusses what features the 034Motorsport rotors have.


1) 2-piece rotors: Like discussed in the earlier sections, the 034Motorsport rotors are true 2 piece rotors. So what does this mean?


a) Replaceable friction rings: The 034Motorsport rotors have removable and replaceable friction rings. This means when you wear out your friction rings you can replace them independently of the hats, and this will result in you saving a significant sum of money compared to replacing the entire rotor. That is if you don’t get it from FCP Euro or Turner motorsport and have a lifetime warranty.

Front friction ring: https://www.034motorsport.com/replac...-m2-m3-m4.html

Rear friction ring: https://www.034motorsport.com/replac...-m2-m3-m4.html


b) Additional air flow to the bell region of the hat: Since these are proper 2 piece floating rotors you get a lot more space between the hat and the friction ring due to the mounting system. This allows for more air flow into the bell region of the hat allowing for better ventilation.


c) Lower weight: The hats on the 034Motorsport rotors are lightweight aerospace grade aluminum to save weight, and they are hard anodized to prevent damage to the aluminum (corrosion, galvanic corrosion - more on this later, etc) and it is more resistant to heat induced color shifting. Also since the hat can mount to the friction ring in select spots, material can be removed where the hat doesn’t need to touch the friction ring. Again this allows more ventilation as discussed in point b, but it also reduces weight of the hat. So the 034Motorsport rotors weigh in at 23.8 lbs for the front rotors vs. 24.0 lbs for the stock front rotors, and 20.6 lbs for the rear rotors (stock rear rotor weight is unknown). So you lose a tiny amount of weight over the already extremely lightweight factory rotors which have aluminum hats.


d) Low thermal conductivity: Due to the 2 piece nature of the 034Motorsport rotors and the minimal amount of surface area that the hat has in contact with the friction rings, the amount of thermal energy that can be conducted to the hat from the friction rings are reduced. This means the amount of heat transferred to your wheel hubs and your wheel bearings are greatly reduced, thereby limiting premature wear and tear of your wheel hubs.


2) Fully floating rotors: The 034Motorsport rotors are fully floating in both the axial and radial directions, and they have anti-rattle springs as well. Let’s discuss the benefits of this, and some features 034 put into their rotors to achieve this:

a) Warp resistant: Since the 034Motorsport rotors will be freely floating in both the axial and radial direction (and thus can freely expand in these directions), these rotors will be incredibly resistant to warping when subjected to incredibly high amounts of heat from braking.

b) Stainless steel hardware: To achieve a fully floating rotor 034 motorsport uses stainless steel bobbins, bolts, and anti-rattle clips (I believe it is A2-70 stainless steel, meaning they are austenitic acid proof stainless steel capable of at minimum 70 kg of tensile strength per bolt - and at 10 bolts per rotor they should have at least 700 kg of tensile strength - which should be more than the rotor ever sees as rotors mainly see shear forces not tensile forces, and the bobbin handles these shear forces not the bolt). This allows for the bobbin and their related hardware to always remain corrosion free regardless if you are driving it in the winter with harsh road salt constantly making its way onto the rotors or not. The stainless steel hardware also benefits over coated steel hardware because as the friction ring slides around on the bobbins and wears away the surface material of the bobbins, there is no risk of corrosion with stainless steel because they do not rely on an outer surface coating to inhibit corrosion. So with stainless steel corrosion is not a problem, and this is excellent because you do not want your bobbins or hardware to fail over time due to corrosion as that would mean catastrophic brake failure. You also won’t have to worry about your relatively thin anti-rattle springs failing over time due to corrosion as this would cause the rotors to rattle around and generate a lot of NVH.

So overall the hardware seems to be excellent quality, and I don’t have any complaints about it, I actually prefer stainless components being used here.

c) Anti-rattle springs: 034Motorsport utilizes anti-rattle springs on the back side of their rotors, this stops the freely floating friction rings from rattling around and causing a whole bunch of NVH which can be annoying on a car that sees street use. This is an incredibly nice touch that allows these rotors to be more liveable.


Now I would like to also discuss the potential of galvanic corrosion because I know this question will come up because you have stainless steel bobbins in contact with an aluminum hat. So for galvanic corrosion to occur you need 3 things: dissimilar metals (with a large enough electropotential difference - i.e. far apart on the galvanic table), electrolyte, and metal to metal contact (an electrical connection). All 3 can be present in our rotor meaning galvanic corrosion is a potential issue, and to stop it we need to eliminate one of these 3 things. We do have 2 dissimilar metals with a pretty big electropotential difference in aluminum and stainless steel, and we can’t use aluminum hardware because they simply aren’t strong enough and moving to metals like steel would reduce the electropotential difference but introduce corrosion which is a different problem. So we have to look at the other 2 factors in stopping galvanic corrosion. We can’t necessarily eliminate an electrolyte if we drive in the winter, but if it is a summer car we can stop galvanic corrosion by keeping our brakes dry, so if you wash your car dry the brakes soon. We can try to eliminate metal to metal contact by having a nylon or fiberglass shim breaking the contact between the aluminum hat and the stainless steel bobbin but that wasn’t done by 034Motorsport - maybe because these materials present as a thin washer wouldn’t survive the high brake temperatures. We could have a sacrificial metal with an aluminum washer, but this might be a bad idea because if the washer disintegrates then we will have a large gap leading to a lot of play in the bobbin system. So what 034Motorsport actually did is utilize a hard anodization on the rotor hat. Hard anodization is essentially anodizing but applied in a much thicker coat and is a lot more durable and temperature resistant than standard anodizing - this is excellent since brake rotors take a massive amount of abuse both from the environment and from high brake temperatures. Since hard anodization is electrically insulating it completely breaks the metal on metal contact and thereby stops galvanic corrosion from ever happening. So this is how 034Motorsport stops galvanic corrosion. So if you ever replace the bobbin system just make sure not to damage the hard anodization on the hat so it retains its electrically insulating properties. On a side note it would be really nice if 034 could also include an electrically insulating washer to increase protection against galvanic corrosion.


If you want to learn more about galvanic corrosion the dark aero guys have an absolutely fantastic video on the process, and it pretty much embodies all the core principles you’d learn in a chemistry course (of course there are more concepts that dictate speed like equilibrium constants and so forth, but that’s pretty irrelevant because we just want to know if this phenomenon occurs or not). Here’s their video below:

3) J-slots/J-hook friction face: The 034Motorsport rotors have a J-hook/J-slot style friction ring face. The benefits of these are as we discussed before: increased brake bite vs straight slots due to the presence of many leading edges, reduced brake fade due to ventilation of brake pad off gassing, superior pad cleaning vs. slots again due to the increased number of edges, enhanced crack resistance as there are no holes, and even heat distribution due to the shape of the j-slots.


4) Directionally curved vanes: The 034Motorsport rotors have 72 and 36 directionally curved vanes for the front and rear rotors respectively. This allows the rotors to act as a radial flow fan and pump air from the bell region of the hat to the outer circumference of the friction ring. This design of vanes allows for increased air flow over straight vanes and enables significantly better cooling. The 034Motorsport front rotors also have significantly more vanes than other competitors and the stock rotors, meaning they should be able to dissipate more heat. The rear rotors on the other hand have a near stock vane count so they should be able to perform as good as stock in terms of cooling in the rear, but I suspect it will perform better than stock due to the increased amount of air that can flow from the front of the rotor to the bell region via the large gaps in the hat.


5) CM-250 Special Alloy Rotor Rings: These friction rings use a specially formulated alloy by a reputable brake manufacturing company. This iron alloy according to 034 is supposed to be extremely resilient to track abuse, so this is a good thing to have on rotor designed for track abuse.


This wraps up my technical overview of the 034Motorsport rotors, and all I can say is I am impressed with what I am seeing so far. Now let’s look at the rotors after they are mounted.


Images of the Rotors on my M2 and fully bedded in:

Now lets look at some images of the 034Motorsport rotors installed on my m2:

Here’s the before:


Credit: F87source


Credit: F87Source



Here’s after the first bed in cycle:


Credit: F87Source


Credit: F87Source

As you can see the matte silver coating (I believe this was an extremely thin layer of metal sprayed onto the rotor to prevent corrosion while the rotors sit on the shelves waiting to be sold) has worn off and a nice even layer of pad material has coated the front and rear rotors. In some spots there are a bit less deposits than the others which is why you see some ring formation, but this should change as the pad material wears even with the face of the friction rings. You’ll also notice that the front rotors have a heavier amount of pad material deposited on the friction ring, and that is likely due to the front rotors being responsible for more of the braking.



Here’s after the 2nd bed in cycle:


Credit: F87Source


Credit: F87Source


As you can see the dark black pad deposits on the front rotors have mostly faded away and the rings are slowly fading as well. I suspect as I rack more miles on the car the pad deposits and rings will begin to fade away completely and leave a smooth shiny finish - like below:



What a completed rotor bedding and break in should look like (I attached an imgur album because there are quite a few images, so feel free to scroll through them):

View post on imgur.com

Credit: PayamFSU https://f80.bimmerpost.com/forums/sh...20&postcount=1




But overall this is what the bedding in and break-in procedure on the 034Motorsport rotors with stock brake pad compound should look like.




And additionally here is an image of rear brake pad clearance, since this can be an issue on 2 piece aftermarket rotors - with some competitors specifying that pad trimming might be required. Fortunately with the 034Motorsport rotors there is a few mm of clearance and trimming of the brake pad is not necessary, this should also be sufficient clearance for any rotor hat expansion - which should be really minimal to non-existent because the hat is very well spaced from the friction ring and therefore will never get hot enough to expand more than these few mm of clearance. (Note: the image showcasing clearance is not very easy to get, and is kind of misleading because of the pad and the rotor hat being at different depths so the hat casts a shadow on the gap making it hard to see the true gap on most photos. But the image below does a pretty good job showing the gap.)


Credit: F87source

The front rotor isn’t really an issue since the gap is much larger between the hat and the brake pad, so clearance there shouldn’t ever be an issue.



If you need help with install here’s a video from FCP Euro showing how to install rotors on the F8X chassis cars:

Driving Impressions with the 034Motorsport rotors:

So I’d like to wrap up my review by going over what my impressions are with the 034Motorsport rotors after driving with them for a few hundred km’s (well almost 1,000 km now). The first thing I would like to note is how quiet they are. Being J-Hook style rotors I expected a lot of extremely loud buzzing and whirring noises that would be audible in the cabin during normal driving (as brake pads are always slightly in contact with the rotor even when the brake pedal is not pushed) and especially during braking - as per the testimony of the guys over on the Audi forums with these 034Motorsport rotors. However, this is not the case at all. What I found was that these rotors in conjunction with the stock brake pad compound (properly lubed ears with anti-squeal to stop squealing and squeaking) are almost as quiet as stock.

Let’s discuss this a bit more:


Before bedding in:

The rotors there was a faint metallic rubbing sound that could only be heard with the windows down.



After bedding in:

The faint metallic rubbing noises are down with the windows up or down.

With the windows up there are no buzzing sounds, there are no whirring noises - absolutely nothing - I literally cannot hear any difference vs. stock.


With the windows down I can slightly make out a buzzing sound only when I drive near a wall or row of parked cars where the sound can bounce back to my ears. It is pretty quiet and I can barely hear it, so the whirring noise that most people report is barely audible at best. This is also when my car is in comfort mode and I am barely on the throttle, in sport+ when my exhaust valves open up and I am on the throttle then all I can hear is my exhaust.

So in summary the anti-rattle clips also do an excellent job stopping all rattling noises from the free floating nature of these rotors, there were no such rattling sounds whatsoever. The J-slots also do not make much noise at all, so that’s not really a concern or a reason to avoid these rotors at all.



Braking performance wise these rotors perform just as good as stock during normal braking pressure, under full braking pressure (as hard as I could push the brake pedal) these rotors again performed just as good as stock if not better. I think my current limitations for braking performance does not lie in the brake system itself but more so in my worn continental tires. So braking performance is excellent and I have no complaints here.


Brake dust generation seems to be just as bad as the stock drilled rotors, so again this is just up to brake pad compound and I am sure ceramic pads will reduce brake dust build up. In terms of brake pad wear it is too soon for me to compare the differences between the drilled rotors and the J-slot style rotors, so I can’t comment on this.


Parking brake performance has actually been better than stock and I am pretty sure this is not a placebo. Since I find these parking brake hats to fit more snugly than the stock ones, I find I have to pull the parking brake a bit less for it to fully hold the car on any incline. In terms of performance they seem to function just as good as stock with the addition that I don't have to pull the parking brake handle as far. I also slightly bedded in the parking brake by driving very slowly and gently pulled up the parking brake handle for a second. I just wanted to deposit some pad material onto the hat so the pads wouldn’t have to grab onto just the bare metal alone.


Fitment was excellent, everything fit as it should during the install minus one of the front rotor bolts not having a base to pinch down on (as described above) since the hole doesn’t taper down - but again this isn’t an issue since the rotor bolts don’t do much beside holding the rotor on when the wheels are off anyways. Other than that fitment was great, and pad tolerances were tight but acceptable by 2 - piece aftermarket rotor standards.


So overall these rotors have been excellent, and I have absolutely nothing to complain about. If anything else notable happens I will try to remember to report back here.



Summary:

In summary the 034Motorsport brake rotors for the F8X BMW M2 M3 and M4 cars are absolutely excellent - I absolutely love the way they look behind the wheels (it really does bring a new dimension of sportiness to the car), I love how quiet they are, and I love the added braking performance they will bring to the car when it heads to the track. The overall fitment, quality, rotor technology, price, and lifetime warranty (when purchased from FCP Euro or Turner Motorsport / ECS Tuning) make this aftermarket rotor an almost unbeatable offering - and this is why I think they are the best offering currently available for the F8X BMW platform. So if you’re in the market for upgraded rotors, I think this is an excellent choice and should be your first consideration.

[F87source]

Just did a review of 034Motorsport's replacement rotor rings for this rotor ugprade incase anyone is interested in what they look like, and I also show the bobbin system in more detail: https://f87.bimmerpost.com/forums/sh....php?t=2077725

[Westersund]

Thank you for an excellent review! Looks to be as good of an option as AP racing or Girodosc.

[F87source]

Originally Posted by Westersund

Thank you for an excellent review! Looks to be as good of an option as AP racing or Girodosc.

Thanks for the kind words!

Yeah these rotors are excellent and on the level if not better than the competition.

I always loved the j-hook designed rotors for the better thermal dissipation to the surrounding metal vs straight slots. They also look better imo.

[dtmurf]

Great info, well written. Thanks as always for the in depth review, it's always good to make an informed decision on something as important as breaks!

[F87source]

Originally Posted by dtmurf

Great info, well written. Thanks as always for the in depth review, it's always good to make an informed decision on something as important as breaks!

Thanks for the kind words! And I agree, it is always critical to know as much as possible when making a big purchase or a purchase for something as critical as brakes. So I tried my best to make the review as encompassing as possible.

[medphysdave]

It would be interesting to see the cost breakdown of the replacement rings across the main upgrade options and inital cost. AP, Girodisc, 034, Paragon. Also the weight of these rotors. I know lightweight isn't always the best due to thermal capacity.

This would bother me. This means the second set screw wouldn’t have anything to bottom down on and therefore couldn’t clamp the rotor to the wheel hub and therefore was useless. This isn’t a really big deal in my opinion, because the single set screw was enough to secure the rotor to the hub and these rotor set screws don’t serve any purpose except to hold the rotor in place when the wheel bolts are off. So there is no structural reason for their presence and not having them shouldn’t affect safety.

I'd want to know if it was on purpose or an oversite before justifying it to be ok. My recent experience with a different vendor had the hats cut to function like the factory hat.

But it's nice to see another quality option. The more vendors means more price pressure and makes sure things don't get out of control for us consumers.

[F87source]

Originally Posted by medphysdave

It would be interesting to see the cost breakdown of the replacement rings across the main upgrade options and inital cost. AP, Girodisc, 034, Paragon. Also the weight of these rotors. I know lightweight isn't always the best due to thermal capacity.

This would bother me. This means the second set screw wouldn’t have anything to bottom down on and therefore couldn’t clamp the rotor to the wheel hub and therefore was useless. This isn’t a really big deal in my opinion, because the single set screw was enough to secure the rotor to the hub and these rotor set screws don’t serve any purpose except to hold the rotor in place when the wheel bolts are off. So there is no structural reason for their presence and not having them shouldn’t affect safety.

I'd want to know if it was on purpose or an oversite before justifying it to be ok. My recent experience with a different vendor had the hats cut to function like the factory hat.

But it's nice to see another quality option. The more vendors means more price pressure and makes sure things don't get out of control for us consumers.

So replacement cost would be pretty good for the 034 motorsport rotors because you will have a life time warranty if you buy it from FCP or turner/ecs.

In terms of weight you want the mass to be in the friction rings and the hat to be really light weight.


The rotor set screws don't do anything except hold the rotor on when the wheel is off. These things strip so easily that I would also use anti-seize on the bolts and just not torque them to spec, and that's likely the only time I'll ever say that. I think 034 made it a single screw hold down design because that allows easier alignment with the hub pins.

[ThreeStripes]

Assuming you would need to buy one set of replacement rings to have that on lifetime replacement as I understand it. Although you may be able to just cycle the full kit including hats.

I haven’t reached out to FCP on it but I am curious how that would work.

[F87source]

Originally Posted by ThreeStripes

Assuming you would need to buy one set of replacement rings to have that on lifetime replacement as I understand it. Although you may be able to just cycle the full kit including hats.

I haven’t reached out to FCP on it but I am curious how that would work.

No, if you buy the rotors from FCP euro then the entire rotors are covered via life time warranty.

[TheHunterHofman]

Another thorough and in-depth review; great job! Really impressed with how far down the rabbit hole you go with these reviews.

[F87source]

I just did a review of 034Motorsport's replacement rotor rings incase you guys want to see what they look like and how the bobbin system works in more detail: https://f87.bimmerpost.com/forums/sh....php?t=2077725

[BigJsmall2c]

Next review for the 6pot rotor options. Lol

[F87source]

Originally Posted by BigJsmall2c

Next review for the 6pot rotor options. Lol

Haha I would love to, but I don't have a 6 pot caliper so it wouldn't be a good review if I couldn't test it on my own car.

[BigJsmall2c]

Looks around at the crowd with hands in the air, "someone get this man some big breaks!"

[///MPhatic]

Originally Posted by F87source

As you can see the matte silver coating (I believe this was an extremely thin layer of metal sprayed onto the rotor to prevent corrosion while the rotors sit on the shelves waiting to be sold) has worn off and a nice even layer of pad material has coated the front and rear rotors.

It's most probably GEOMET360, which is a top tier rust/corrosion inhibitor.
Unfortunately, I don't believe it's available to consumers.

[F87source]

Originally Posted by ///MPhatic

It's most probably GEOMET360, which is a top tier rust/corrosion inhibitor.
Unfortunately, I don't believe it's available to consumers.

Possibly, but you also don't want this to be on your friction rings because it's not going to be great for coefficient of friction. It's only there to prevent corrosion while the rotors on the shelf and it's meant to wear off really fast during break in. It was literally an insanely thin coating, when I mounted the rotor and spun it, just the pads rubbing against it wore lines through the finish.

[F87source]

Originally Posted by BigJsmall2c

Looks around at the crowd with hands in the air, "someone get this man some big breaks!"

Haha I'd love to do a bbk, but I don't have the money for it right now haha (especially this year, I'm replacing a LOT of components on the car and it's going to add up lol).

[///MPhatic]

Originally Posted by F87source

Possibly, but you also don't want this to be on your friction rings because it's not going to be great for coefficient of friction. It's only there to prevent corrosion while the rotors on the shelf and it's meant to wear off really fast during break in. It was literally an insanely thin coating, when I mounted the rotor and spun it, just the pads rubbing against it wore lines through the finish.

GEOMET wears off very quickly, it's super thin.

[F87source]

Originally Posted by ///MPhatic

GEOMET wears off very quickly, it's super thin.

Yes exactly that my point. Im just saying it's for protection during storage and nothing more.

[Andrew2]

Another thank you for the excellent information, here and elsewhere in the Forum - absolutely first class

[F87source]

Originally Posted by Andrew2

Another thank you for the excellent information, here and elsewhere in the Forum - absolutely first class

Thanks for the kind words!