Hi all. I have a 2008 535XI wagon, and I have recently added a lot of power to the vehicle. The brakes are underwhelming at best, and are not confidence inspiring by any means. I am looking for recommendations for a brake upgrade, and I am also looking for a wheel size that will work with larger brakes.

I understand Evan Patak wrote a fantastic DIY for upgrading to E60
M5 brakes which I am leaning towards (for cost), however I have heard these brakes will not clear most 18” wheels. As I would really like to stick with 18” as a size, can anyone recommend a high performance solution that doesn’t need a 19” wheel to fit?

 

Are you running stock BMW brakes?

Give this a read:

Brake Rotor Information

www.turnermotorsport.com

BMW brake rotors are excellent - vented and oversized for the application. When combined with a capable brake pad they provide superior braking performance even under mild track and autocross situations. The venting and sizing is key because brake rotors store heat (see below) and the added mass of oversized discs helps prevent 'warping'. In over twenty years of BMW racing and tuning we have never seen a warped BMW rotor.
It's a common misconception that simply changing brake rotors will improve your stopping performance. This will only prove true under extreme conditions - track events and racing - and only with rotors such as BMW's Euro and Performance parts. For the majority of us, the standard OEM replacement rotors will be more than sufficient for the type of driving that we do.
The brake rotor acts as a heat bank. Heat is stored in the cast iron of the rotor as the brake pads create friction. The central vanes of the rotor direct air through the casting, venting the rotor of the heat and also cooling it at the same time. A larger rotor has more capacity to store heat and can thus, provide better stopping performance for greater lengths of time. This is one reason why racecars typically have big brakes. Too small of a rotor for the application will lead to the heat being trapped with the rotor and overheating the rest of the brake system.
This makes a difference in your rotor choice because a standard brake rotor has more mass and will act as a better heat bank than one that has been drilled and/or slotted. It has become necessary to drill or slot the rotors for other reasons - mainly to allow an exit for gases that build between the pad and the rotor. The gas needs an escape so that it does not block the application of the pad to the rotor. But newer technology has made these types of rotors nearly obsolete (although they look pretty cool on a street car). None of the street pads produce this gas and there are very few race pads that still do. One benefit to slotted or drilled rotors is that the edges of the holes and slots can graze the pad material, which will decrease pad life but help maintain heat in the pad (critical for track pads). Note that the Turner Motorsport rotors have their holes and slots chamfered to allow smooth transit of the pad over the rotor surface. One other thing to note: a drilled and slotted rotor will have less mass and less braking surface than any rotor - these are mainly for looks.

What does all of this mean to you?

On a street-driven car with street pads, the typical driver will see no benefit to using a cross-drilled, slotted, or two-piece Motorsport rotor over a standard OEM replacement rotor. There are small benefits to using one of these on a street car - looks/aesthetics, drainage for water, for instance. There's nothing wrong with using a different rotor on the street and we would not discourage that. But if you're looking for better braking on the street, first upgrade your pads and consider the rotor design to be an aesthetic choice.

For more in-depth and scientific explanations, see StopTech's excellent technical pages:

 

Thanks, I've had several BMWs and am familiar with the information you've posted. The issue isn't stopping performance-it's warping and brake fade. I was looking for a high performance solution that would allow me to run 17 inch wheels, but it seems the best solution for me is to grab a set of rear M5 hubs and go ahead with the E60 M5 brake conversion as well as move a size up to 18s.

 

As mentioned in the article, your problem is not the rotor size, but most likely the choice of pads. I doubt that you are driving at harsher than track or autocross conditions, which your stock rotors can handle. Rotors do not warp, even at high temperatures. They do, however, develop deposits from the brake pads due to the high heat These deposits will cause vibration similar to warped rotor. It sounds like you need to carefully consider all-ceramic brake pads. Or, you are simply trying to rationalize purchasing M5 brakes!.

 

Maybe, but I had similar issues with EBC reds as well. I do drive the car very hard, in temperatures above 100º, and frequently find myself slowing down from 160+mph runs. I understand what you're saying, but simply put the OEM brake configuration isn't adequate for my needs, even with aggressive pads and good fluid. The M5 brakes seem like a great solution for now, until I can find a fabricator to help me design a bracket adaptor for something stronger down the line. I think next step might be trying out the EBC yellows, but I'd rather stop putting money into the current setup and do the M5 conversion.