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Old 06-25-2004, 12:00 AM   #1
SupraTT&WRX
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Default 245/40/17's in the rear. 225/45/17 in the front

How would this effect handeling. There is only a .1" differance in rolling height? Will it hurt anything?
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Old 06-25-2004, 12:34 AM   #2
abaxter34
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understeer gallor. if you really have your heart set on staggered tires id put the fat ones up front. even though its only .1" difference, i think your diffs might not like it in the long run.
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Old 06-25-2004, 09:45 AM   #3
Nick M
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switch it around, bigger in the front, wrx's arent rwd
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Old 06-25-2004, 02:07 PM   #4
subieworx
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You have your cars confused. Besides there is more fender clearance up front for the larger tires, plus handling will be better. The diffs would not be happy though. All tires are supposed to be the exact same rolling diamter. Subaru even goes as far to say that all tires should be replaced at the same time, for example if you have a blow out replace all four not just he one as it could cause problems.
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Old 06-25-2004, 06:33 PM   #5
Rally1
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It's not the absolute ride height that's the issue, its the (resulting) rolling circumference you have to worry about, can't be more than 1/4" different.

So as a guess 17" wheels and tires might have a diameter of say 22" vs 22.1"

c= 3.14 * 22

69.08 vs 69.394

so it would cause issues with those numbers, you need to get the ACTUAL numbers to be sure, or better yet measure the actual circumference with a soft tape.
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Old 06-25-2004, 06:39 PM   #6
Rally1
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To followup, i'll use real numbers from a set of specs on the Falken ST-115's

3.14159265358979323846

245 40 17 = 24.7"
225 45 17 = 25"

77.597" vs 78.540" almost an 1" !

Not good for the diff.
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Old 06-26-2004, 09:17 AM   #7
subieworx
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Uummmm...pi.
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Old 06-26-2004, 12:24 PM   #8
Chuck H
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Quote:
Originally posted by Rally1
To followup, i'll use real numbers from a set of specs on the Falken ST-115's

3.14159265358979323846

245 40 17 = 24.7"
225 45 17 = 25"

77.597" vs 78.540" almost an 1" !


Not good for the diff.
Take that analysis one step further:
245/40-17 = 77.60" circumference = 816.5 revs/mile
225/45-18 = 78.54" circumference = 806.7 revs/mile.

Assuming you're travelling at 60 mph on the highway, the plates in your center differential have a 10 RPM difference in speed. I know that Subaru has that 1/4" overall circumference spec on tire size difference, but that one has always seemed to me to just be a legal trick to always give them an excuse to never replace a diff under warranty. Because if that spec is true, it means that the diff can't tolerate more than a 2.5 RPM rotational difference without being damaged, and in that case, they have no business selling it. If you believe their specs, then an 80 thousandths of an inch difference in tread depth due to uneven tire wear is enough to throw you out of spec and void the warranty on your differential.

I'm not saying that running different sized tires is a good idea, but I don't think it's really as destructive as they'd like you to believe as long as the tires are close.
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Old 06-27-2004, 01:16 AM   #9
Rally1
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Quote:
Originally posted by Chuck H


I'm not saying that running different sized tires is a good idea, but I don't think it's really as destructive as they'd like you to believe as long as the tires are close.
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