Originally Posted by 73azbronco
Any reference out there to find true tire sizes versus stated for the different brands of 33 or 35's?
Example, I have Toyo open country, they are stated at 35 inches, but measure a surprising 33.75 inflated to 30psi. Until I measured them, I would have sworn they were easily 35.
FOUND THE ANSWER!!!!
Look at the mfg's stated revs per mile.
20,168 / [insert rev's here] = more realistic actual size.
For example, your tires (MT's?) have 596 rev's per mile, which equals 33.8". Much closer than the 34.8" inflated diameter spec.
Originally Posted by Ferrachi
I wasn't happy that a set of Duratracs I bought (31") measured out just a tad over 29". Wasn't what I expected at all and realized I had some researching to do. Use google, many other posts on this forum and others which talk about this.
and yours are 681 revs, which is 29.6"
A 35" circle has 576 rev's per mile.
A 33" circle has 611 rev's per mile.
A 31" circle has 650 rev's per mile.
I've found that most 35" tires are in the 595-605 range.
33's are mostly in the 630's.
I'm not sure about 31's.
I haven't looked into it, but I believe the discrepancy comes from load bearing. The inflated diameter spec is the tire inflated to maximum psi, with no load. Revolutions per mile is probably the tire at it's maximum psi and
load, meaning the tire has it's flat spot at the contact patch resulting in a shorter radius to the ground (which is half the functional diameter of your tire).
Hope this helps someone.