whitegoose wrote:my particular size of g-force is a 205/55R16, which measures 8.4" wide on a 6.5" wide rim. using your math skills and the rule of thumb i posted above would give you a width of 8.2" on a 6" wide rim (width of my stock rim).

that makes a 205/55R16 actually work out to about 208 mm wide on a 6" wide rim. (8.2" * 25.4)

now, take the 225/50R16 from the same spec sheet...

which measures 9.2" wide on a 7" wide rim.

use your math skills and rule of thumb... that's 8.8" wide on a 6" wide rim.

now more math skills... that's about 223 mm wide on a 6" wide rim


more math... 223 mm - 208 mm = 15 mm
the 225/50R16 actually works out to about 15 mm wider than the 205/55R16... thats 5 mm less than what it is supposed to be if you just look at the sizes written on the sidewall.

15 mm / 25.4 = .6" wider

ok, so its more than a quarter of an inch, but its still less than the near .8" wider you said it should be.

Don't forget that the bead width of a tire is considerably lower than the section width (the actual size of the tire). While a 225 might have a section width of 8.85, the bead width of a 50 series is usually more like 7.35 (3/4" more narrow on each side). Also, it depends on the specific tire, as some tend to bulge more by design from the bead width.

The other thing is that the lower the series, the larger the tread width with the same section width. So even though the 225 only has a .8" greater section width than the 205, the tread width difference may be an inch or more (again, depending on the specific tire).