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Old 06-17-2017, 11:52 PM   #34
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300mm Brakes and 15" Wheels

So in the above thread we thought a little thought of fitting 15" wheels over 300mm brakes, below are my findings!

Courtesy of spidertri who has a 3.0i z3 with 15x8 et20 TRM wheels. As a reminder the z3 3.0i has 300mm vented front brakes.

My own testing:

I was able to find a set of Turner Motorsport 12.5mm spacers on craigslist, and since I still have my style 13 wheels that are 15x7 et47, with the 12.5mm spacer I would sit at et34.5 and I was hoping that would be enough clearance for the 300mm brakes. But it wasn't.

Here on the dirty backside of my wheel you can see the line of contact from the caliper on the inside of the wheel. The wheel won't even turn! When I stacked the two 12.5mm spacers on top of each other and then tried to put on the 15" wheel, (25mm spacer in effect) resulting in et22 the wheel rotated freely. This was only for testing!! DO NOT put two spacers on top of each other.. But it did give me some more proof that a wheel with low et20's 15" can fit over 300mm brakes.

Looking at the dirty mark it shows that if pushed out more away from the narrowing of the wheel it would have clearance from hitting the wheel. The green shows where the wheel narrows and as a results hit the caliper, so having lower offset helps give the clearance needed to fit 15" wheels over the 300mm brakes. As seen with spidertri's 15" wheels.


To be safe (what most of us know already):

15" Wheels: 286mm brakes* (e36: 325/328/318, z3 1.9/2.3/2.8 e46: 323)

16" Wheels: 300mm brakes* (z3: 3.0i, e46: 325)

17" Wheels: 315mm brakes* (e36 m3, z3m) AND 325mm brakes* (e46 330)

*technically just rotor size!

Possible! *at your own risk!

15" Wheels: 300mm brakes - with low ~ 20 and lower et
16" Wheels: 315mm brakes - with low ~ 20 and lower et AND 325mm brakes - not sure exactly, but I know some people run 16" special winter wheels on e46 330 cars, so 16" over 325mm is also possible, but you need to make sure the wheel is designed to fit!

One thing that is also important, is that if for some reason you bend your wheel with hitting a big pothole or something with wheels being very close to the caliper you run the risk of also damaging your brakes, so having extra some clearance is also safer in the case of accidental damaging of the wheel.

Best Budget Choice?

When doing brakes for the 318ti usually we switch out pads and rotors, so that cost is there and how much is spent based on rotor/pad type is dependent on buyer. What I read and HAVE NOT CONFIRMED! is that caliper that we have stock with the 318ti with a e46 325i carrier will bolt on over 300mm rotors!

As a result:

The only parts needed for a front and rear brake upgrade that is even better than OEM BMW 6cyl e36 328i/is brakes, and puts us at the stock ~2900lb 220hp z3 3.0i brake power are:

- e46 325 front carrier + stock caliper
- rear 6cylinder z3 caliper
- Your choice of 300mm vented rotor + stock rear rotor size and then pads.


***328ti Build thread. ***

Even more important:
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Last edited by anassa; 06-18-2017 at 12:02 AM.
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