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Warning: If you're considering purchasing new wheels/tires for the XI
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12-26-2008, 02:07 AM | #1 |
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Warning: If you're considering purchasing new wheels/tires for the XI
You will have problems if the rolling diameter is not the same or off by around 1% or more (the 1% is a recommended tolerance reported by others on this forum).
- you will trip your DTC while driving normal - you may blow up your transfer case - you will not be happy Can an admin make this a sticky at the top? I saw more threads/questions pop up and want to make sure people who are new to the XI, and wouldn't even think to search for DTC + new wheels/tires unless they encounter a problem (after it's too late), read this prior to purchasing new wheels. Related posts: http://www.e90post.com/forums/showthread.php?t=190455 http://www.e90post.com/forums/showthread.php?t=186089 Thanks |
12-28-2008, 05:19 PM | #2 | |
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12-28-2008, 07:07 PM | #3 |
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Not that I disagree with the advice of matching front and rear diameters, but where does this magical 1% threshold come from other than some members mentioning it? Is it from a BMW engineer or something? If its on the Internet it must be true...
Again, it makes inherent sense to keep the diameters the same to preserve the clutch pack, but I just question what the appropriate threshold is. |
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12-28-2008, 11:42 PM | #4 |
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I think "1% tops" is another way of saying "as close to 0% as you can".
Granted that if you run staggered wheels, you'll have a hard time getting to 0%... but something "as good as zero (aka some low % like 1%)" will suffice. -scheherazade |
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12-29-2008, 07:56 AM | #7 | |
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Long answer: I've been on this forum for more than 2 years. As far as I can tell, this 1% figure came from a group of former Subaru owners who knew that their Subies had a 1% overall rolling diameter tolerance. This is true for Subarus that have viscous center couplings as their AWD system (which would be most manual transmission models, except for the STi). The reason for this is that a viscous coupling is not a particularly heat or stress tolerant form of differential, and the fluid in the coupling can overheat and break down over time if the axles that feed it are constantly spinning at different rates. Of course, xDrive doesn't use a viscous center coupling. It uses an electromechnical clutch pack, with a heat-resistant clutch. I've never seen anything that provides a specific tolerance for an acceptable difference in rolling diameter between front and rear wheels. During a trip to my local independent service shop about a year or so ago, I was flipping through the SA's xDrive dynamics manual, and saw a secton on wheels. I remember that the manual said that the xDrive system can tolerate differences in wheel diameter, but I don't remember there being anything specific about how big of a difference was acceptable. I was just sort of flipping through the book though, and I wasn't really looking for an answer to this question, so it may be in there and I may have just missed it. If any SAs out there have their xDrive dynamics training manual, and can lay this issue to rest once and for all, I would welcome it. EDIT: To clarify, my post should not be read as suggesting that you will have no problems if you put monster truck wheels on the rears and heelys on the fronts. My point is simply that, so far, I have never seen any real basis for the 1% figure.
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Last edited by Lassaxi; 12-29-2008 at 02:58 PM.. Reason: Clarification |
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12-29-2008, 07:56 AM | #8 |
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Finally! Someone else understands the true issue!
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12-29-2008, 11:39 AM | #9 |
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Seriously, there are a lot of people running staggered on the XI platform and so far I've only see one person reporting DTC light on but it was because he put on wrong-sized tires. I've been running staggered on both the old and new XI for 1.5 years and neither car has detonated, nor have I been attacked by a Polar Bear yet.
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12-29-2008, 12:26 PM | #10 |
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I'm a little confused. Most of the posts seem to indicate people think a staggered setup is bad with the xi, but you're saying some people argue the opposite?
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12-29-2008, 12:48 PM | #11 | |
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12-29-2008, 02:37 PM | #12 |
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The point of starting this thread was to let current or future XI owners know if you plan to run a staggered setup, make sure the rolling diameter of your wheels are as close to 0% as possible before going out and buying the wrong sized tires/wheels like I did, so for a fact, 245/40/18 rear with 225/40/18 front (on stock staggered rims) is out of tolerance. By the way, what do polar bears have to do with this thread? I may be too old or young to understand the reference... Someone please enlighten me....
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12-29-2008, 02:49 PM | #13 |
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nevermind about the polar bears reference... I did a search for polar bears and staggered setup and was viciously chased by a polar bear... good thing I'm running a staggered winter setup or I would've been done for.
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12-29-2008, 03:43 PM | #14 | |
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Also, this spec is true for both viscous center diff WRX and multiplate clutch pack STi I'm biased because I am a 'former Subaru owner' but if I had a xi I would use that Subaru spec in the absence of an equivalent BMW spec because all AWD systems have an ideal rolling diameter difference of 0% and an overly tight spec is much better than $$$$ differential damage |
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12-29-2008, 03:56 PM | #15 |
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Well, stock xi with Sport Pkg and 18 inch wheels is staggered
What if one tire is under or over inflated by let's say 5-10 psi? would that cause a problem?
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12-29-2008, 05:16 PM | #16 | |
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Would it cause a problem with the differentials? I'm not sure but I suspect it would not because I don't think that difference in pressure will change the tire's diameter very much (driving an AWD with one flat tire (conventional tire with no air) would be a big problem though) |
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12-29-2008, 06:27 PM | #17 | ||
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12-29-2008, 09:21 PM | #18 | |
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Last edited by nicknaz; 12-30-2008 at 12:59 AM.. |
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12-29-2008, 11:53 PM | #19 |
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12-30-2008, 12:24 AM | #20 | |
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12-30-2008, 01:07 AM | #21 | |
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I frankly have no idea why the tread depth specs appear to be more relaxed in your outback. Impreza service has the same spec for all cars |
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12-30-2008, 04:48 AM | #22 | |
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I suppose the possibility exists that the dealer simply lied to me and got away with it, but I've had one tire with 17,000 fewer miles on my OB wagon for the last 20,000 miles or so, and haven't had any problems with the AWD system. That reminds me- it's nearly time to start looking at new tires! I also didn't realize that VTD was available on any of the Imprezas. I've also never owned an Impreza, so that probably exlpains that.
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Last edited by Lassaxi; 12-30-2008 at 05:41 AM.. |
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