255/65R17 tire size — what each step costs at the fender

Mid-size pickups and body-on-frame SUVs, and the base fitment on several full-size crossovers.

Half of the difference lands at the axle

A tire's centre sits at the axle. When the overall diameter grows, only the bottom half of the growth pushes the axle upwards — the top half raises the crown of the tire and consumes arch clearance instead.

Alternative	Diameter	Diameter change	Ride height change
245/65R17	29.54 in	0.51 in	0.26 in
265/65R17	30.56 in	+0.51 in	0.26 in
245/70R17	30.50 in	+0.45 in	0.23 in
255/70R17	31.06 in	+1.00 in	0.50 in
265/70R17	31.61 in	+1.56 in	0.78 in

Both figures matter and they answer different questions. Ride height is what changes at the sill and at the bumper. The full diameter change is what has to fit between the crown of the tire and the top of the arch, and it is twice as large.

Whether either figure fits a particular vehicle is a measurement on that vehicle, taken through the full range of suspension travel and steering lock.

Its counterparts on other wheels

255/60R18, 255/55R19 and 255/70R16 all measure within 0.01 in of this size — the same 10.04 in casing on four wheel diameters, differing only in sidewall depth.

The overlap on a 17-inch wheel

This diameter is where the 17-inch catalogue stops being a crossover range and starts being a light-truck one. 245/75R17 at 31.47 in and 255/75R17 at 32.06 in are classed as light truck; 255/70R17 at 31.06 in and 265/70R17 at 31.61 in are not, despite sitting between them. The classification follows what manufacturers actually build in each size, not the arithmetic.

Sidewall and load

6.53 in of casing puts this size firmly in utility territory rather than passenger. The load index printed after the code varies considerably between the passenger-standard and LT constructions sold under it, and the LT versions reach their rating by holding a much higher pressure rather than by being a different shape.

That is why capacity is published as a table of pressures rather than a single number: the same casing carries different weights at different inflations, and the placard states which point on that table the vehicle was certified at. The tire pressure and load tables reference works through the relationship, and the comparison tool covers the geometry for any pairing.