275/70R18 vs 285/70R18

By the formula, diameter increases from 33.2 in (842 mm) to 33.7 in (856 mm). Section width increases from 10.8 in (275 mm) to 11.2 in (285 mm). Sidewall height rises from 7.6 in (193 mm) to 7.9 in (200 mm).

Nominal revolutions per mile fall from 608 to 598. The diameter increase adds 0.28 in (7 mm) of ground clearance at the axle. The scale drawing and differences table show these unloaded, formula-based dimensions, not measurements of a specific tire.

By the formula, changing to 285/70R18 makes true speed 61.0 mph at an indicated 60 mph. At an indicated 100 km/h, true speed is 101.7 km/h. Actual distance traveled is likewise 1.7% greater than the odometer indicates.

At 65 mph with a 3.73 axle ratio and a 1.00 transmission gear, nominal engine speed falls from 2,458 rpm to 2,418 rpm, down 1.6%. The formula-only axle ratio that restores the original engine speed is 3.79: 3.73 × 33.71 / 33.16. The gear ratio calculator shows the relationship between diameter, axle ratio and engine speed.

The Firestone, Nitto, Kumho, Toyo and Mickey Thompson tables represented here list 20 tires in 275/70R18: 19 LT versions and 1 passenger version. Published diameters span 33.19–33.62 in, with load ranges SL and E.

For 285/70R18, Toyo and Nitto list 4 tires, all LT and load range E, with diameters of 33.7–33.98 in. Toyo lists its Open Country A/T III at 33.2 in in LT275/70R18 and 33.7 in in LT285/70R18. The measured-model tables show why the specific model matters alongside the nominal size.

For more nominal ground clearance and lower engine rpm at the same road speed, 285/70R18 moves in that direction. Its taller, wider dimensions also require more space around the tire.

275/70R18 is the shorter, narrower option and retains the starting size’s nominal gearing relationship. Fit depends on the vehicle, wheels and suspension; compare the specific tire’s published dimensions and approved rim widths.