215mm=8.47" (tire width)
75% of 8.47"=6.35" (side wall)
6.35"x 2=12.71" (both side walls)
12.71" + 16"= 28.71" (side wall plus rim)
That's the math that I've been using. Now, I ain't no
mathematician by any means, but that seems to
correspond with the calculators on line.
Here's one calculator which I just looked up:
http://tire-size-conversion.com/tire-size-calculator/ Also at that site are tires by diameter, a long listing of
30" tires, which as Ken mentioned on the first page does list
a series 85 Michelin tire. They have no listing of those
on their site. The site that I'm referencing does show a
Michelin LTX A/S - 215/85R16 tire. This would be great it they are available.
http://tire-size-conversion.com/tires/Michelin/LTX-AS-215-85R16.htmWhen you go to look that size tire up all you find are
M/S 2 or A/T 2. Nothing in an A/S or summer tire.
Now, so how did you arrive at 31.5 diameter? The tires that
have been on my truck for the past decade or just short of
a decade and approximately 14-15k miles, are also Cooper
SRM II 8.75xR16.5LT M&S tires:
http://www.pbase.com/dennygraham/image/160954025 They're the ones I want to replace with Michelin's in a 16"
hoping for a better ride, less vibration and at 30" a little
more speed on the highway. The distance those tires roll
inflated to 50psi is:
90.25" divided by 3.1416 = 28.72" rolling diameter.
http://www.pbase.com/dennygraham/image/160954029 dg
