265/50R20 — the Grand Cherokee's 20-inch fitment

The Jeep Grand Cherokee WK2 is the one vehicle in this catalogue recorded with 265/50R20. It is also recorded with three other factory sizes, and the set is unusually tightly grouped.

The WK2's four factory sizes

Size	Wheel	Diameter	Difference from 265/50R20
265/50R20	20 in	30.43 in	—
295/45R20	20 in	30.45 in	+0.02 in
245/70R17	17 in	30.50 in	+0.07 in
265/60R18	18 in	30.52 in	+0.09 in

Nine hundredths of an inch separates the tallest from the shortest, across three wheel diameters and three section widths. That is a manufacturer holding rolling diameter constant while changing everything else, so that one speedometer calibration and one set of stability-control constants serve every trim.

What does change across those four rows is sidewall. This size carries 5.22 in of it — the least of the four, and a consequence of wrapping the largest wheel. The 17-inch option has 6.75 in.

The rest of the 20-inch band

Below it, 245/50R20 is 0.79 in shorter and 0.79 in narrower. Above it the gap is large: the next catalogued 20-inch size is 245/60R20 at 31.57 in, +1.14 in and 3.75%, followed by 275/55R20 at +1.48 in.

That gap exists because 20-inch tires are produced either as low-profile crossover sizes, which is what this is, or as tall light-truck sizes, and very little sits between the two groups.

Circumference is 95.6 in and revolutions per mile works out at 662.7. The 295/45R20 alongside it on the same option sheet turns 662.3 times — four tenths of a revolution apart over a mile, on tires 1.18 in apart in section width. The relationship between diameter and revolutions, and why width plays no part in it, is set out in the revolutions per mile reference.

The same band, one wheel further out

The trade this size represents does not stop at 20 inches. 275/45R21 stands 30.74 in — 0.31 in above it — on 4.87 in of sidewall, and it is the only 21-inch size in this catalogue.

Line the group up by wheel and the pattern is complete: 6.75 in of casing on the 17, 6.26 in on the 18, 5.22 in here on the 20, and 4.87 in on the 21. Four wheel diameters, four sidewall depths, and a total variation in standing height of 0.31 in from the shortest to the tallest.

Whatever a buyer is choosing between those four, it is not ride height and it is not gearing. Every one of them puts the axle at the same place and asks the drivetrain the same question.