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Old 05-16-2006, 04:53 AM   #1
QwikRex
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Default How much variance in tire diameter is bad for center diff?

I decided to rotate my tires today and figured I might as well check out the tread depth on my Yokohama AVS ES100's. Tread depth of the front tires were at 4/32 of an inch and the rears were at 5/32 of an inch. I checked the circumference of the front vs. rear tires and the difference between them was about 0.197 inches. Is this within spec enough to not damage the center diff?
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Old 05-16-2006, 06:03 AM   #2
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1/4" is the max according to subaru.com and your owner's manual.
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Old 05-16-2006, 10:20 AM   #3
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That's 1/4" rolling circumference, not diameter.
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Old 05-16-2006, 05:10 PM   #4
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Cool, then I should be ok then.
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Old 05-16-2006, 11:41 PM   #5
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Quote:
Originally Posted by Mulder
That's 1/4" rolling circumference, not diameter.
OMG seriously? 1/4" is a very small difference.

I searched NASIOC for exactly this info when I needed new tires, and couldn't find jack (My car didn't come with an owner's manual). Now 2 months later I see this.

I have a set of 235/40/17 on rear and 225/45/17 on front.

Is the damage serious? How much of a concern is this?
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Old 05-17-2006, 08:30 AM   #6
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1/4" circumference equals approximately 2/32" difference in tread depth on a 215/60/16 tire. I think the 1/4" difference may be consider may be conserative but, do we really know?

Last edited by Hayes; 05-17-2006 at 08:32 AM. Reason: Add a Comment
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Old 05-17-2006, 09:10 AM   #7
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Quote:
Originally Posted by Silverpike
I searched NASIOC for exactly this info when I needed new tires, and couldn't find jack
http://www.subaru.com/common/faq/tech_info.jsp#4
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Old 05-17-2006, 06:01 PM   #8
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Quote:
Originally Posted by UkNuck
That doesn't exactly help, especially since the relevant question now is: what sort of damage is possible to the diff?

Won't the diff just get a little hotter? It is a viscous unit, which should be tolerant of F/R bias.
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Old 05-17-2006, 09:02 PM   #9
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It will blow your center diff and yes it does happen. Just like when your car is towed by two wheels.
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Old 05-18-2006, 10:33 AM   #10
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it's absolutely ridiculous. it makes the donut spare a failure waiting to happen.

if you keep your speed low there shouldn't be a problem. the lower the better.

i suspect soa is covering their asses so that they do not have to provide warranty coverage for ANY vc failures.

Quote:
Originally Posted by some dealer
ok, we checked it out, and we found some stuff that's broken. problem is, your tires have more than 0.25" rolling circumference differential. i know you don't want to hear it, but sorry, we can't warranty that. your total cost comes to $500 for a new diff, and $700 for the labor.
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Old 05-18-2006, 11:39 AM   #11
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I believe the owner's manual has specific directions on the use of the spare, ie. you must enable FWD only with the fuse under the hood (for the 4EAT at least) and I think that the spare goes on either the front or back in an ideal situation.

I carry AAA and would insist on a flatbed for towing.

Bill in SD
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