Is smaller spare ok on AWD?

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It will not help the drivetrain to do this. The little bit of money you save here can cost you big $$$$$$ down the road in excessive wear in the transfer case components.

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"miles" < snipped-for-privacy@nopers.com> wrote in message
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miles wrote:

While I agree that running mixed tire sizes on a AWD or 4 wheel drive is a bad thing, these two particular tire sizes are so close in diameter that it will do no harm. The stock tire size will roll 661 times in a mile. The new tire size will roll 660 times. That is only one tire revolution difference in a full mile. This will cause your vehicle no harm.
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I'm not sure if you have your math quite right but I did notice it with my PT 4WD with exactly the same tire combination.
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"Nosey" < snipped-for-privacy@removethis.hotmail.com> wrote in message
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TBone wrote:

It may have been tire pressure or even a tread pattern difference you felt. Even if you can notice the difference while driving it's not enough of a diameter change to cause any damage. If it's only going to be used as a spare it shouldn't matter much.
I didn't do any math. I cheated. I used this: http://www.miata.net/garage/tirecalc.html
I checked the website math against my own and it came out pretty close.
245/70/17 tire: 245/25.4*2*70/100+170.5039" diameter 30.5039*3.1415927.83" circumfrence. 63360/95.83f1.170 revs per mile
265/65/17: 265/25.4*2*65/100+170.5629" diameter 30.5629*3.1415927.016" circumfrence 63360/96.016e9.890 revs per mile
The difference is 1.28 tire revolutions per mile. IMHO, not enough to cause any damage.
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Fair enough. I didn't feel it during normal driving but had one hell of a time getting it into and out of 4WD and could feel it pulling while in it. I thought that my transfer case was acting up until I remembered that my spare was still the old size and when I removed it the problem went away. I don't know where they are getting these numbers from but my 265's were at least an inch taller than my 245's, not .06 taller like the chart says but if the tires that Miles is switching to are also just about the same diameter as the old ones, then he should be fine.
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"Nosey" < snipped-for-privacy@removethis.hotmail.com> wrote in message
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TBone wrote:

The 245 and 265 in the tire size is the section (tread) width in millimeters. It doesn't tell you the diameter.
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