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Unread 10-15-2004, 01:57 PM   #1
SureThing
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Metric vs. Standard tire sizes

Some where I read a 265-75-15 is about the same thing as a 31x10.5x15. What is the metric size for a 30x9.5x15?

Also, in general, how do you figure it out?

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Unread 10-15-2004, 02:12 PM   #2
BigWaylon
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there are several websites that will convert for you...but, there's obviously math behind the whole thing...

you need to know two things:

1. what the "measurements" on the tires are
2. there are approximately 25.4 millimeters in an inch

knowing those two things, you can go from standard to metric and back...

31x10.50x15
31 = tire height in inches
10.50 = tread width in inches
15 = rim size in inches

265/75/R15
265 = tread width in millimeters
75 = profile ratio (width divided by the sidewall height)
15 = rim size in inches

to get the metric size for a 31x10.50x15:

10.50*25.4 = 266.7 (your new width in millimeters)
31 (height) - 15 (rim opening) divided by 2 = 8 (16/2) (which is your sidewall height)
8/10.50 = .76 (new sidewall ratio is 76)
so, your 31x10.50x15 is actually a 267/76/R15, which is very close to your other tire


to get the standard size for a 265/75/R15:

265/25.4 = 10.43 (your new width in inches)
265*.75 = 198.75 (sidewall height)
198.75*2/25.4 + 15 = 30.65 (your new height in inches...take the sidewall, multiply by 2 to account for top and bottom, divide to get number in inches, and add rim opening in inches)
so, your 265/75/R15 is actually a 30.7x10.43x15...also very close to your other tire...

hope that helps...

Greg
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Unread 10-15-2004, 02:53 PM   #3
SureThing
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Thanks. I found this link

http://www.onlineconversion.com/tire...conversion.htm
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