This information is courtesy of Doug Schaefer ~ dgs.
You can get the diameter for any modern tire size pretty easly. Lets take the 225/75R14:
225 = The section width in mm
75 = Aspect ratio, in this case the side wall is 75% as tall as the section width. So, 225mm x .75 = 168.75mm
R = Radial
14 = Wheel diameter in inches.
So, there are 2 side walls, one up top and one at the bottom. 168.75 x 2 = 337.5mm.
Next, we need to convert that to inches. 337.5mm / 25.4mm per inch = 13.287 inches.
Add that to the 14 inch wheel diameter and you get 27.287 inches.
That said, for reasons I'm not sure of, tires of different brands in the same size have slightly different outside diameters. Also, the outside diameter will vary depending on the width of the wheel it's installed on.
Also, if you go to Coker's web site Coker Tires and look up the bias ply 800-14 and 850-14, you'll find the heights listed there. The 800 was 27.58" tall and the 850 was 28.10" tall. That's the only source I've found for heights of the originals.
When I bought my rims & tires, I wanted to get as close to the original diameter as practical so they'd fill the wheel wells. My 235/55R17's are 27.18" tall, theoretically, which is pretty close in my book to the 800's anyway.
Hope that helps.
DGS (aka salguod)
Created 15 February, 2011
Last Edited: 15 February, 2011
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