Jeep Grand Cherokee (WK2): four factory sizes, 1.97 in of width, 0.09 in of height

Held to within a tenth of an inch

• 245/70R17 — 30.50 in
• 265/60R18 — 30.52 in
• 265/50R20 — 30.43 in
• 295/45R20 — 30.45 in

The spread across the whole factory range is 0.09 in, or 0.28%. Four wheel-and-tire packages spanning three wheel diameters, and the rolling diameter barely moves.

Where they do differ is across the tire. Section width runs from 9.65 in on the base fitment to 11.61 in on the widest — 1.97 in of variation — and sidewall from 6.75 in down to 5.22 in. This platform's trim ladder is a width ladder, not a height ladder.

The two 20-inch sizes are not variations on a theme

265/50R20 and 295/45R20 sit on the same wheel diameter and differ by 1.18 in of section width, with the wider one carrying a lower aspect ratio to hold the same height. Between them they cover the road-biased and the performance-biased ends of the range, and they read identically on the speedometer.

Why the upgrades here are small

Not one of the three recorded steps reaches 6.3% of the factory diameter:

Fitted	Diameter	From 245/70R17	From 265/50R20
275/60R18	30.99 in	+0.49 in (1.60%)	+0.56 in (1.84%)
265/70R17	31.61 in	+1.10 in (3.61%)	+1.17 in (3.86%)
285/55R20	32.34 in	+1.84 in (6.03%)	+1.91 in (6.27%)

An independent-suspension unibody SUV with a low load floor and, on many examples, an air suspension that changes ride height on its own is not a platform where four-inch tire increases happen. The recorded upgrades reflect that: the largest of them is +1.91 in.

265/70R17 from 265/60R18 is a notable one — zero change in section width, +1.09 in of height, achieved entirely by moving one wheel size down and ten points of aspect ratio up.

What the constant diameter is protecting

Holding four packages to a tenth of an inch is not tidiness for its own sake. A vehicle certified with one speedometer calibration, one set of gear ratios and one brake-control configuration across its whole range is cheaper to engineer and simpler to support, and the tire sizes are where that consistency is bought.

It also sets the tolerance for anything an owner fits afterwards. The factory itself never varied rolling diameter by more than 0.28% across four packages — which is a reasonable indication of how much variation the vehicle's systems were designed to see, and a useful reference point when a candidate size turns out to be 6% away.

Nothing on this platform needs a gearing conversation

At 3.61%, a size change is inside what a modern multi-ratio transmission absorbs by shifting differently. It shows on the instruments — an indicated 70 mph becomes 72.5 — and it barely shows in how the vehicle drives.

The ratio column is empty here, and given the size of the changes involved it costs the arithmetic very little — nothing on this page moves the effective final drive by more than a few percent. The gear ratio calculator will take your own ratio if you want the engine-speed figure exactly.

The air suspension complicates the clearance question, not the arithmetic

Where an air system is fitted, the vehicle's own ride height varies by several inches between its settings, so "does it clear" has more than one answer on the same vehicle on the same day. The geometry above does not change with ride height; the contact does.

That is the unusual thing about this platform: on most vehicles clearance is one measurement, and here it is a set of them. A tire that never touches at the raised setting can find the liner at the lowered one, and the size code contains nothing that would tell you which.