Metric vs. Standard tire sizes -

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post #1 of 3 Old 10-15-2004, 01:57 PM Thread Starter
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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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post #2 of 3 Old 10-15-2004, 02:12 PM
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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...

31 = tire height in inches
10.50 = tread width in inches
15 = rim size in inches

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...


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post #3 of 3 Old 10-15-2004, 02:53 PM Thread Starter
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