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      06-23-2016, 12:05 PM   #1
paris1
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Why do E89s wear out rear tires faster than fronts?

Anyone have a theory for this phenom? I put on a set of Bridgestone Potenza S04 Pole Positions about 9k miles ago and checked the tread depth yesterday. 4/32" on the rear and 6/32" for the front. Wear pattern is excellent. I was hoping they would wear better than this and my wife just retired from a job wherein she commuted over a twisty mountain road every day, so this might with have something to do with it. But I'm still left wondering why a none-heavy car like the Z4 (that in this case is not driven all that hard) consistently wears out rears faster than fronts?

Edit: Just looked up the weight distribution and it turns out it close to 50:50; in fact slightly biased towards the rear!

Last edited by paris1; 06-23-2016 at 12:35 PM..
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      06-23-2016, 01:46 PM   #2
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Its rear wheel drive - all BMW's go through two rears for a set of fronts - Well mine do anyway
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      06-23-2016, 03:50 PM   #3
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Quote:
Originally Posted by BIGBOYQ View Post
Its rear wheel drive - all BMW's go through two rears for a set of fronts - Well mine do anyway
That sounds plausible, but I've owned other rear drive vehicles that do not do this. why would a BMW be more inclined to do so?
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      06-23-2016, 04:29 PM   #4
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The wider rear tires (geometry), as well as the BMW "lean" (more geometry), and the fact they are the drive axle (your foot) all contribute to this.

Pretty typical for BMWs across the product line. 2x rears to each set of fronts.
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      06-23-2016, 05:01 PM   #5
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Quote:
Originally Posted by Lurcher View Post
The wider rear tires (geometry), as well as the BMW "lean" (more geometry), and the fact they are the drive axle (your foot) all contribute to this.

Pretty typical for BMWs across the product line. 2x rears to each set of fronts.
I've read this enough to know that it's normal (for a BMW). Just wondering why (for example) my three previous 2WD pickups never did this. Nor did my 390 CID Ford Galaxie w/4 spd and posi (obviously from a previous life!) or two previous Miatas do it.

Last edited by paris1; 06-23-2016 at 05:31 PM..
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      06-23-2016, 11:11 PM   #6
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All sports/sporty cars that I've owned wore out quicker on the drive wheels than non-drive wheels. Trucks are lighter in the back unless you always have it loaded. Not sure about Miata.

My wife's 535i has xDrive, but still wears more on the rear than the front, just not as huge of a difference compared to the 2WD cars.
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      06-24-2016, 07:34 AM   #7
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[QUOTE=paris1;20152069]I've read this enough to know that it's normal (for a BMW). Just wondering why (for example) my three previous 2WD pickups never did this. Nor did my 390 CID Ford Galaxie w/4 spd and posi (obviously from a previous life!) or two previous Miatas do it.[/QU

Mostly due to the wider rears. The geometry places more cornering load on the rear tires. The rear are wider not only for traction, but to prevent oversteer. And just because you don't feel it, don't assume the tires are not spinning a little bit when you get on it, it's just so minimal - but it still takes it's toll.

Talk to guys on other BMWs who have went to a square setup (same size tires all 4 corners) and this issue (mostly) goes away. Another benefit is they can rotate tires. Some of the guys tracking their cars go to a square setup to actually build in the oversteer.

I used to drive a dodge colt (front wheel drive) in high school in the 80's that was the opposite - 2 sets fronts to a set of rears - and I know that was my right foot doing it...
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      06-24-2016, 09:33 AM   #8
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I realize you mentioned you have owned other RWD cars that did not do this before, but honestly all RWD sports cars are going to wear out the rears first...
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      06-24-2016, 10:53 AM   #9
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Quote:
Originally Posted by 2011z435is View Post
I realize you mentioned you have owned other RWD cars that did not do this before, but honestly all RWD sports cars are going to wear out the rears first...
You may be right and the tendency to do this on my two Miatas was masked by 5k mile tire rotations.
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      06-24-2016, 07:26 PM   #10
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You're putting 300HP down on the rear tires. That's why.
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      06-24-2016, 08:36 PM   #11
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Originally Posted by jparnes1 View Post
You're putting 300HP down on the rear tires. That's why.
And the fronts are doing all the turning. Hence, the question.
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      06-28-2016, 01:00 PM   #12
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Quote:
Originally Posted by paris1 View Post
And the fronts are doing all the turning. Hence, the question.
The rear tires will have a bit more slip, even at stock n54 levels. You may not notice but if you exit a corner with a bit of throttle the rear will slide just a bit. Also hard acceleration will give you the slightest slip.
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      06-28-2016, 03:08 PM   #13
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Quote:
Originally Posted by jts1981 View Post
The rear tires will have a bit more slip, even at stock n54 levels. You may not notice but if you exit a corner with a bit of throttle the rear will slide just a bit. Also hard acceleration will give you the slightest slip.
All that and there's no doubt more camber change at the rear plus the fact that you can't rotate to even the wear. Those are all good reasons for the rears to wear out first. Never thought I'd miss those 5k tire rotations. Oh well!
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