Ed,
I found my notes from talking to Goodyear.
I'd asked them about a LT235/85R16 truck tire. They told me 657 rev/mi
which works out to an effective diameter of 30.71 inches. If you take the
std formula for figuring the diameter of a tire you get 31.73 inches.
The section width of this tire is 235 mm. 235/25.4 = 9.25 inches.
Height of the tire section is 9.25 * 0.85 = 7.86 inches.
The dia is (7.86 * 2) + 16 = 31.73 inches
That's about a 3.3% difference.
Steve
That's 'cause rev's/mile is based on the static loaded radius of the tire,
not the 'free' dimension as measured. An 8-10 ply 235/85 doesn't give up as
much dia. as a flotation size(typically at 'normal' pressures). As noted,
rim width also affects SLR.