Anyone know the formula to calculate the diameter of a tire from the numbers posted on the side wall?

 

i.e. 205/50/15 = 205mm width/50% sidewall w/ respect to the width (205mmx50%)/ on 15" rims.

so, your side wall is 102.5mm.

So, (102.5mm X 2) + (15"x25.4mm/inch) = 586 mm for a 205/50/15 tire mounted on a 15" rim. (or ~23.07" for the tire and the rim)

[edit] fixed conversion factoer. 25.4mm/inch


[Modified by Cosworth, 6:10 PM 1/27/2002]

 

The numbers are pretty easy:

say 205/50 R15
that means, 205 mm wide, 50 percent of that width is the sidewall height, and it's a 15 inch rim size.

But if you're lazy like me: http://www.rx7turboturbo.com/robrobi...e_diameter.htm

 

thanks

 

I think it's 20.5 for each sidewall, or 41 for the top and bottom. 10.25 mm sidewall would be SUPER low profile

 

fixed the mistake along w/ the conversion factor.

 

This may be nitpicking, but do you ever notice that a 15" wheel is not really 15". Same goes for all other sizes.

 

simple. for a 205/50-15 tire it is as follows... 205 (width)x .50 (sidewall) x 2 (there are two sidewalls, the top and bottom) divided by 25.4 (25.4mm = 1 inch) + 15 (rim size) = 23.07 inches. a 195/55-15 would be 195 x .55 x 2 divided by 25.4 + 15 = 23.44 inches.

 

how do you figure? a 15 inch tire is 15 inches inner diameter. what are you referring to?

 

Like shoes, there's variation all over the place. A falken azenis 205/50 is alot wider than a touring tire's 205/50. But the inner diameter pretty much has to be accurate, otherwise the tire wouldn't seal to the wheel, though the seal is made against the inside of the wheel and the outside of the tire's sidewall, so there is some room for error.

 

If you measure lip to lip on the ITR wheel, it is 16" and some change. I'm sure the inner diameter is 15" as you say, but its just weird to look at the ITR wheel and know its 15" although its actual size is 16".

 

heh, never actually bothered to measure that <gets tape measure>

edit: ha! from now on my volks are 17 and a quarter's!


[Modified by Aleph, 1:04 AM 1/28/2002]