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      11-23-2017, 07:46 PM   #49
dre99gsx
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Drives: 1994 Toyota Supra
Join Date: Aug 2011
Location: NJ

iTrader: (2)

Z4M inner depth is 54mm on the dot. So you are looking at 13mm shorter.

I tried bolting on a 335i rear brake caliper, and IT FITS (you need to add 1/2" thick washers/spacers and longer bolts).

Also:
335i rear caliper = 7.8lbs
Z4.0si rear caliper = 6.6lbs

Z4M rotor = 14.8lbs
Z4M brake shoes (for two) = 1.6lbs

Z43.0si rotor = 14.2lbs
Z43.0si brake shoes (for two) = 0.8lbs

Doing the upgrade would add 1.4lbs per corner This doesn't include any brackets I need to make to move the caliper, nor the fact that I'll need to weld up the brake shoes one on top of the other. So I would assume the upgrade would actually add 1lb for the bracket (6061 alum) and 0.8lbs more for the original shoes, total would be 3.2lb per corner. OUCH

And, then there is the brake bias:

Z4M = 60mm/46mm pistons (f/r), 345mm/328mm rotors (f/r) (14mm diff in piston, 17mm diff in rotor)
Z43.0si = 57mm/40mm pistons, 325mm/294 rotors (17mm diff in piston, 31mm diff in rotor)

You can see the Z4M has a much smaller variation in piston/rotor diff front to rear, but it's also possible the proportioning system is also different (master cylinder?). So, I have no idea if in the end, both vehicles had the same brake bias.

For me to upgrade to the 335i rears (which are 44mm pistons) and Z4M rear rotor, this would be my final setup:
2JZ4 = 57mm/44mm pistons (f/r), 345mm/328mm (13mm diff in piston, 17mm diff in rotor).

So, the rear would not only get a larger rotor, but larger piston, and larger brakepad, all which may significantly increase rear bias more than I want. Yes, I would get much closer to the piston/ring combo from the Z4M, but what I don't know is if the proportioning system/valving in the brake system is also the same proportion. Why would BMW put such a small rear rotor on the 3.0si when the Z4M is vastly larger??? They must have compensated for it somewhere else.

I looked at my pads from the last event, and they all wore pretty evenly front and rear - I suspect my bias is "just right".

I can run my smaller pad in the rear, it fits, therefore reducing the amount of bite, and bias to the rear.
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Last edited by dre99gsx; 11-24-2017 at 11:22 AM..
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