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Tire Size Question


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7 replies to this topic

#1 Richard1296

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Posted 08 October 2006 - 06:04 PM

As luck would have it there is a small problem with the 2000 Impreza Outback
I just bought. It appears one rear tire has been intentionally cut on the
sidewall, deep enough I don't trust it. Would replacing just the two rear tires
with the same size and brand be safe. The existing tires have about 2/3rds
of their tread left and I don't want to replace all four unless absolutely
necessary. I measure the front tires at 9-10 / 32ths tread left.I cannot find
the tread depth of the tires when new (Goodyear Assurance 205/60R15).
No idea if they are expensive or cheap tires either.

Richard

#2 Ranger83

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Posted 08 October 2006 - 06:26 PM

I believe the owner's manual has words to the effect of "same manufacture or design."

If I were in your shoes, I'd

1. Buy two new tires and mount them on the front. Some A/S's are 11/32nd when new (Michelins), some are 10/32nds (Potenza RE92A's).

2. Move the tires currently on the front to the back.

3. Either keep the remaining tire as a full-size spare, or sell it on craigslist or ebay.

Are they TripleTreds? They're relatively expensive, but 15" tires aren't bad. The tires are the only part of your car that touches the road, so having four good ones with winter coming on is a Good Thing.

At goodyeartires.com you can find the tire catalog to get the original specifications, like rolling diameter, loaded radius, and # revolutions per mile.

#3 porcupine73

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Posted 08 October 2006 - 06:30 PM

All the tires need to be within like 1/4" circumference or whatever or you're asking for trouble.

#4 Richard1296

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Posted 08 October 2006 - 06:42 PM

I expect the tires to be within 1/4 inch . I guess a little
more air in the old ones and a little less in the new ones
would alter the diameters a small amount. If the tires
originally had 13/32ths tread depth the drop to 9/32ths
would be 1/4 inch. in diameter. I would expect tires
on any car to not wear exactly even all around. Though I
guess thats why they should be rotated.
I dunno...maybe the cost of two Goodyear Assurance
is going to be close to that of four of another brand.

Richard

#5 porcupine73

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Posted 08 October 2006 - 07:29 PM

On EndWrench Subaru recommends using a thin blade tape measure to determine circumference. It takes little more than 1/32" tread wear difference to exceed the 1/4" circumference threshold. Hm..I think I better check mine!

#6 johnceggleston

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Posted 09 October 2006 - 07:49 AM

my calculator says 1.273/32" difference in tread wear to hit 1/4" circumference difference. in other words, NOT MUCH>


On EndWrench Subaru recommends using a thin blade tape measure to determine circumference. It takes little more than 1/32" tread wear difference to exceed the 1/4" circumference threshold. Hm..I think I better check mine!



#7 outback_97

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Posted 09 October 2006 - 09:58 AM

FWIW:

I was overdue to rotate my tires, I've driven around 10,000 miles on them since purchasing them... finally got around to doing it this weekend. I measured both rears at exactly 7' 1-1/8"... the fronts were 7' 7/8" for a difference in circumference of 1/4". Should have rotated sooner... in 10K miles I was at the max threshold that SOA recommends for difference in circumference. It's a pretty tight spec.

Steve

#8 johnceggleston

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Posted 09 October 2006 - 08:40 PM

FWIW:

I was overdue to rotate my tires, I've driven around 10,000 miles on them since purchasing them... finally got around to doing it this weekend. I measured both rears at exactly 7' 1-1/8"... the fronts were 7' 7/8" for a difference in circumference of 1/4". Should have rotated sooner... in 10K miles I was at the max threshold that SOA recommends for difference in circumference. It's a pretty tight spec.

Steve


well hopefully there is a safety factor built into that 1/4" number, but i wouldn't bet on it. to expensive to repair if you are wrong.




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