There are differences in actual diameter between different brands of
tires and tread wear, however, the basic math is...

  tirewidth x ratio of sidewall x 2 / 25.4 (to convert millimeters to
inches) + diameter of wheel = diameter of tire.

[ 215 (mm) x .55 (ratio) x 2 (we're doing a diameter so it's in two
places) ] / 25.4 (mm's to the inch) + 16 (wheel diameter) = 25.31
inches
[ 205 (mm) x .70 (ratio) x 2 / 25.4 ] + 14 = 25.29

That's close enough not to worry (70% was the ratio on the tires not
75)...but let's do the match with 75% ratio tires...

[ 205 x.75 x 2 / 25.4 ] + 14 = 26.1

Standard tires (without a ratio value have the sidewall being 80% of
the tread width....)

[ 185 (mm) x .80 x 2 / 25.4 ] + 14 = 25.65

Syncro enthusiasts recommendation

[ 215 x .75 x 2 / 25.4 ] + 15 = 27.70

On Apr 18, 2005, at 1:27 PM, JordanVw@AOL.COM wrote:

> i talked to benT and he reccomended a 215-55-16 tire..  but someone
> else told
> me that this is "same as stock" rolling diameter of a 205 75 14???