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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Fri, Sep-04-2015, 03:08:50 PM   #1
sept29th
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Default Offset/tire size calculations

I know this topic has been covered a million times, and I have researched for hours. I've studied the examples from Apex that have been incredibly helpful (http://www.bimmerforums.com/forum/sh...-Fitment-Guide). I'm after some feedback on the setup that I've almost settled on. See if there's any glaring thing in my guess work.

It's currently on stock suspension and wheels, with spacers that I despise. So I'd like to get some wheels with correct offsets/widths to do away with the spacers, and get coilovers with camber plates.

This is a semi-DD that will see tracks a few times a year hopefully. On 18 OEM setup.

Considerations:
- No stupid camber. I'm thinking -2.5F -1.5 will do nicely.
- No stupid stretch. I prefer meaty tires now. I'll probably run my rears on the fronts (255/40/18) to start with as they've got heaps of life. Will likely stay in the 40 profile range for the fronts.
- Not going to slam it, but probably a healthy 1~1.5inch drop so that it will look nice, lower cg, not screw up geometry
- I'd like to avoid rolling/cutting fenders if I can help it. Perhaps a light roll, but I'd really rather not. I would rather increase camber slightly than roll, or go down a tire size/offset.
- I don't plan on getting BBK so inner clearance shouldn't be much of an issue.
- I'll probably get a set of progressive springs for comfort

My guess work:
- F: 9.5+25. This sticks out by 42mm (compared to stock 18x8+47). Should fit with -2~3 camber with 255/40/18.
- R: 10.5+24. This sticks out by 21mm (compared to stock 18x9+26). Should fit with ~1.5 camber with 275/35/18. 275/35/18 will have -1.5% smaller rolling diameter, but I think this will be fine. 285/35/18 will be much closer but not too sure about clearance.

Obviously my guess work is... well, guess work. The wheels I'm looking at will set me back quite a bit of $$$ and they offer custom offsets so I'd like to get it as close as I can.

So I welcome any first hand experience while I continue gathering more raw data to improve on my guesstimates.. Cheers!

P.S.
The most aesthetically pleasing setup I've seen is this one. But I suspect he would've made some compromises I'd rather not make such as stretches and bodywork. The spec is 9.5+29, 11+17. Probably A disk front and O disk rear. I'm detecting moderate camber and lowering that I can live with but the stretch is probably slightly much and I won't run a 11 for that reason. But, it is very close to what I'd like my m3 to look like. I guess I want a nice daily that looks and handles good, with minimum compromise. A tough target.

http://www.m3forum.net/m3forum/showthread.php?t=454601

The altnernatives are going OEM 18 square with the popular 265/40 setup or Apex ARC 8 9.5+35 squared route that will free up a lot of options. But I'm leaning towards a perfect width/offset that don't require any spacers as it won't be track oriented.

Last edited by sept29th; Fri, Sep-04-2015 at 03:24:45 PM.
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Old Sat, Sep-05-2015, 05:57:19 AM   #2
RedM3/4
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Default Re: Offset/tire size calculations

You've said what you don't want (problems from teh setup mostly), but not what your real goals are.

my 9.5 et35 track setup sticks out enough that leaving them on too long nicked up sides of my car some from throwing up junk; no way I'd do +25, will just be worse.
This also looks a bit odd w/o spacers as you're splitting the difference in front and back, so fronts stick out and rears are sucked in. So you won't be able to do what most of us call square (equal width and offset to allow rotation); you could do same width rims at different offsets so you could move tires off rims, not a totally bad option since rears go twice as fast as fronts for most of us.
The wider you go, the worse the tramlining will be, and lower the gas mileage.
If you go square, you lose the tendency to understeer near limits, which honestly is the safest setup for most folks on the street, especially if you've not driven the car on the track to get a feel for the back stepping out.
I didn't check your tire sizes much, but also, with 9.5 et35 in front, you won't be able to go taller in front, as you'll hit the spring perch.
YOu can run this setup without doing anything odd to the car:
18 x 9 Front , offset is +38,
18 x10 Rear , offset is +27,
A few mm of offset from here shouldn't be a problem, like a +35 front, +25 rear.
You can do lots of things more aggressive than this, but you're then really into details of alignments, height, and fender rolling.

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Old Sat, Sep-05-2015, 12:20:57 PM   #3
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Default Re: Offset/tire size calculations

If your car is daily driven and you are looking for the perfect setup, I would recommend that you consider your tire size carefully. My car is my DD, I have square 9" 18's and put 265's up front. It looked meaty as hell, but I did not like the way it drove. It would tramline on the highway and follow all the imperfections in the road. I went back to 245/275, still looks good, and handles nicely for a DD.

Here's what my current setup looks like:
-2.3 camber, 12mm spacer in rear, ride height 13.5" F, 13.75" R
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Old Sat, Sep-05-2015, 01:13:38 PM   #4
sept29th
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Default Re: Offset/tire size calculations

Thanks. Interesting point on throwing junks up the fender. Even at factory settings I noticed lots of stone chips on the rear fenders.. I guess sometimes the 'sexy bulges' have their costs..

Not going square, from what I've determined so far, as it won't be track oriented. I like tail happy cars personally, but it just seems that I'll have to make a call at some point and live with it. I think those numbers are conservative and I should be able to squeeze 5mm more.

I am indeed leaning towards 245/275. Currently my ideal spec is 18x9.5+30 10.5+24 . These are slightly more aggressive than what RedM3/4 suggested. These stick out a little more but I'm banking on the assumption that a little more camber should tuck them right in, without going over -2.5.

I'm really looking for a perfect setup that won't require excessive camber or spacers. Hence the difficulty as you can imagine At least today I've played with the wheels to see what they might look like.. I've confirmed that increasing track by more than 40mm (from 18" oem) will require some significant compromise. With 'stock camber' it will take a good 30mm increase in track at the front, but not much more without change in settings. With 2 degree extra camber it should take 7mm more.

On a side.. what's the factory camber at factory height? I realize the acceptable range is something like -0.4~1.2 but that's pretty rough.
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Discussing Do you grease on Derlin Pedal Bushing ? in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)