[BMW DIY Guy]

Hey all

I have read the posts, checked realoem and am trying to figure out what actually FITS with my setup.

From my VIN
18"lt/aly Wheels Double Spoke 397

I have the standard "grey" brakes, not the M sport setup. Realoem seems to read 340x30 or 370x30, but cant tell the difference for which I might have.

What I am trying to figure out is the usual question what actually will fit for a BKK? ECS Tuning says the BMW BBK for my car are 370x30 front and rear.

For example when I look at possible Brembo BBKs I see:

365x29 (assume it will fit)
380x32 (10mm bigger, anyone make these fit?)

I assume the 365s will be fine.. but would do the 380s if I could.

Thoughts?

[johnung]

I have a 2015 335i x-Drive which had the exact same brakes that you have. I did exhaustive research and upgraded my brakes last summer. I could write a book on this subject and have written a bunch of stuff about brakes on other posts. You didn't really say what you want to accomplish with your brake upgrades but here is some input....

If you have grey front calipers, they are 4-piston Brembos with 340mm rotors. The blue M Sport brakes also have different 4-piston Brembos but they use the 370mm calipers. The pads are exactly the same size so there really isn't a difference in braking power on the fronts. Despite the front pads being the same size, the factory uses different pad materials for the standard vs the M Sport calipers. Neither factory pad is all that great and they produce a lot of sticky dust.
So you can't really upgrade the braking power of the front brakes unless you go super expensive with 6-piston calipers, super lightweight rotors, etc. You are talking a really heavy duty track setup here! You can make a difference in front brake performance by changing to better pads such as Hawk 5.0 pads and stainless steel brake lines. You can make your front brakes prettier by going with drilled rotors and painting the calipers with G2 Epoxy Caliper paint and adding a variety of decals in various colors. I wire brushed my rotor hats and painted them silver with G2 also and they look beautiful.

Where the M Sport brakes shine is really with the rear brakes. The standard grey rear calipers are usually 1-piston Bosch. They actually use the same exact pads as the front calipers. The blue M Sport rear calipers are actually 2-piston Brembo that use larger rotors and pads. One-piston calipers on the rear makes the car nose dive when braking hard. Two-piston calipers on the rear make the car squat very controllably under hard braking. New pads on the rear like the Hawk 5.0 make a big difference. Stainless steel brake lines make a difference too. I painted my rear rotor hats with silver G2 caliper paint too. They clean right up from any brake dust, don't rust, and always look brand new.

Option#1) The quickest, cheapest thing that you can do to really enhance your brakes is to go with Hawk 5.0 pads and stainless steel brake lines (set of 4 Stoptech SS lines are roughly $100) Oh, change out the single screw that holds on each rotor with a stainless steel screw. The original screws all rust and weld themselves on and then its a bitch to remove the rotors.

Option#2) The next step up is to find a pair of used rear blue Brembo 2-piston brake calipers and the used rotors that go with them. Be careful that you get the correct blue calipers because I think that BMW sold different blue calipers for different models as their M Sport brake kits. They aren't all the same. Turns out that the Brembo casting numbers are meaningless on the calipers so you can't go by them. The easiest way to tell that they are correct is if the used rotor that comes with it measures correctly. It should be 345mm X (I don't recall but I have it somewhere). You can buy these blue rear calipers new from BMW and the rotors cheaper in the aftermarket. But if you have patience you can find them for about a third of the price on the forum postings.

All those other aftermarket brake packages are really expensive and designed more for show than actually performing better than this Option#2 on the street. If you want Option#2 to look prettier you can always go with a drilled front rotor along with using G2 to paint all of the calipers any color that you want plus add custom decals in any color.

Option#3) These are really what I'd call the BMW Brembo racing brakes with 6-piston front calipers and 4-piston rear calipers with superlight multi-piece drilled rotors. This costs many thousands of dollars and is incredible overkill for the street compared to what option #2 provides.

I'm curious what you are looking to do with your brakes? Hope this helps!