235/65R17 tire size — one rung of a five-step ladder

Mid-size crossovers and SUVs in their base wheel specification — Highlander, Pilot, Grand Cherokee, Murano and similar — sit on this size, as do a number of full-size saloons with all-wheel drive.

Five rungs, 0.51 inches apart

Size	Section	Diameter	Revolutions per mile
225/65R17	8.86 in	28.52 in	707.3
235/65R17	9.25 in	29.03 in	694.8
245/65R17	9.65 in	29.54 in	682.8
255/65R17	10.04 in	30.05 in	671.1
265/65R17	10.43 in	30.56 in	659.9

Every rung is 0.51 in of diameter and 0.39 in of section width, and the whole family spans 2.05 in from bottom to top. This is the longest evenly-spaced run in the catalogue, and it exists because the 17-inch crossover market is deep enough to support five widths at one aspect ratio.

Revolutions per mile falls by roughly twelve per rung, which is the figure the axle ratio is multiplied against to give engine speed. Four rungs of width take the count down by nearly fifty revolutions per mile — a 7.18% change in diameter — which is far from trivial in gearing terms. A vehicle calibrated for the bottom rung and fitted with the top one would show an indicated 70 mph at an actual 75.0 mph.

Closest match, one wheel size up

235/60R18 measures 29.10 in — 0.26% away, on the same 9.25 in section. That is the plus-one counterpart of this size, and the two run in parallel across whole model ranges.

235/75R15 is closer still at 28.88 in, 0.52% below, with 6.94 in of sidewall on a 15-inch wheel. It is the same nominal tread on a fifteen-year-older wheel package.

Six inches of casing on a 17-inch wheel

6.01 in is more casing than any passenger-class 17-inch size below it in the table carries, and it is what keeps a heavy crossover comfortable on a comparatively small wheel. It also means the loaded rolling radius differs from the free radius computed here by more than a low-profile size would — the overall diameter and rolling radius reference sets out why.