245/70R17 tire size — five codes inside a tenth of an inch

Mid-size pickups and body-on-frame SUVs in their base and mid specifications — Tacoma, Colorado, Frontier, 4Runner — plus a number of full-size half-tons at the bottom of their range.

Thirty and a half inches, six ways

Size	Wheel	Diameter	Difference	Sidewall
265/50R20	20 in	30.43 in	0.07 in	5.22 in
245/75R16	16 in	30.47 in	0.04 in	7.23 in
245/70R17	17 in	30.50 in	—	6.75 in
265/60R18	18 in	30.52 in	+0.02 in	6.26 in
265/65R17	17 in	30.56 in	+0.06 in	6.78 in
265/70R16	16 in	30.61 in	+0.10 in	7.30 in

Total spread: 0.17 in across four wheel diameters, from a 16-inch light-truck fitment to a 20-inch crossover one. Sidewall runs from 5.22 in to 7.30 in — a range of over two inches — while the standing height barely moves.

Every vehicle that offers several wheel packages is doing some version of this. What makes this particular diameter crowded is that it is where mid-size trucks, full-size crossovers and the smaller end of the half-ton market all converge.

Reading the table the right way round

The useful question is not which of these is tallest. It is what each one gives up to reach the same height. The 20-inch entry spends nearly two inches of sidewall on wheel diameter; the 16-inch entry spends nothing and is 0.79 in wider at the section into the bargain.

Neither is better. They are different distributions of the same total, and only the vehicle decides which fits.

Symmetric five-point steps at 245 mm

245/65R17 is 0.96 in shorter at 29.54 in and 245/75R17 is 0.96 in taller at 31.47 in — five points of aspect ratio in each direction at 245 mm, symmetric because the width and wheel are held. 255/70R17 is 0.55 in taller at 31.06 in.

The spare on a mid-size truck

Vehicles in this size very often carry a full-size spare of the same code, slung under the bed or mounted at the rear. That makes the spare geometrically identical to the road tires and, after a few years, nothing like them in age or tread depth. Where the spare is a smaller emergency unit instead, the diameter mismatch is real from the moment it goes on; the spare tire sizes reference covers both cases.