M235i rear disks with Porsche calipers question

[Eau_Rouge111]

Hi all,

I have KW V3 on order for my car and am also considering my options with respect to the brakes. Anyone with the front Stoptech or Brembo big brake kits who have gone the rear 996 Porsche caliper adapter route for the rear brakes ever try to fit the rear 345MM x 24MM disks off a M235i? instead of running the stock disks? Does it work, if not, why not? The 996 calipers are make to accept a Porsche 24MM wide disk (as far as I understand it), identical to the thickness of the M235i rear disk...thicker...more robust, better cooling etc etc etc. So before I rip into my car this winter...anyone know if this combo can be done? Or will clearance issues such as adding the M4 front calipers to the front end of the car stop this...or hand brake issues?

[3002 tii]

What about offset?

[Eau_Rouge111]

Originally Posted by 3002 tii

What about offset?

I don't follow, how does the offset affect what brake disks to use?

I posted this same question on the M3forum.net and one member suggested the 911 gt3 calipers with the custom brackets on e9X M3 rear rotors...

I happened to pick up a set of 996 calipers ending in 421/422 (part number) and they as far as I understand it are made to work with a 24MM wide disk...

I also have a set of junk rear e9X M3 rotors I picked up on ebay for mock up purposes...going to try this out over the winter...see how it all fits...I will just need to fab custom brackets to pull all this off...will probably 3D print them in ABS plastic for mock up purposes only...if it works...I'll copy them in ASI 1045 steel which is a good steel for this sort of thing...very hard but not brittle.

[GuidoK]

From what I can see the m235i offset is bigger than the z4m. that means that disc will probably hit either the back plate or even the conrol arm (when back plate removed).
Also it seems that the m235i has 160mm ebrake?
So that also doesnt work.

If you make your own brackets, you can get away with less offset, but hardly any more offset.

You also have to see what offset is possible with the porsche calipers, as in placing of the boltholes in the calipers in relation to the mounting lugs on the control arm.

[Eau_Rouge111]

Originally Posted by GuidoK

From what I can see the m235i offset is bigger than the z4m. that means that disc will probably hit either the back plate or even the conrol arm (when back plate removed).
Also it seems that the m235i has 160mm ebrake?
So that also doesnt work.

If you make your own brackets, you can get away with less offset, but hardly any more offset.

You also have to see what offset is possible with the porsche calipers, as in placing of the boltholes in the calipers in relation to the mounting lugs on the control arm.

Ohh...makes perfect sense...thanks for clearing that up for...so if this does work then it will be with the E9X rear disks...over winter i'll mock it up given I already have all the parts minus the brackets...see how it goes.

The reason I'd like to run the E9X or the M235I is if I run the 380MM front BBK...it seems that a 350MM rear disk by 24MM wide may be a better match for the front brakes but I'm no where near even doing the calculations for brake balance yet.

[GuidoK]

Dont worry too much about the brake balance. Its going to be rear balanced no matter what combo you're going to use. The MBC has afaik quite a rear balance preference. Or are you going to dismantle that and measure up both individual mbc pistons too?

And its very hard to predict exactly how much as you're going to use different pad sizes. If brake coefficients were completely linear and temperature indifferent this wouldnt matter but as this only is true in a theoretical case it does matter.

Build it and if you want to adjust something, go with a more aggressive pad front or rear (depending on what you want to achieve)
As long as you scale up front and rear brakes somewhat linear (so not a 260mm rear disc and 380mm front disc...) you'll be allright.
But doing some calculations is always fun

[Eau_Rouge111]

Originally Posted by GuidoK

Dont worry too much about the brake balance. Its going to be rear balanced no matter what combo you're going to use. The MBC has afaik quite a rear balance preference. Or are you going to dismantle that and measure up both individual mbc pistons too?

And its very hard to predict exactly how much as you're going to use different pad sizes. If brake coefficients were completely linear and temperature indifferent this wouldnt matter but as this only is true in a theoretical case it does matter.

Build it and if you want to adjust something, go with a more aggressive pad front or rear (depending on what you want to achieve)
As long as you scale up front and rear brakes somewhat linear (so not a 260mm rear disc and 380mm front disc...) you'll be allright.
But doing some calculations is always fun

All valid points! thanks. I just need to see if the E9x rear disk will fit first and not affect the hand brake operation...thats the first thing...thanks again for the input!