TireSizesFinder

275/65R17 vs 255/65R18

255/65R18 is 0.02 in (0.6 mm) shorter than 275/65R17, a −0.08% diameter difference. With the speedometer set for 275/65R17, an indicated 60 mph is 60.0 mph on 255/65R18.

Is this a safe swap?

Diameter difference −0.08%: under 1%

By overall diameter alone, 255/65R18 is a near match for 275/65R17; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 275/65R17 (31.07 in) vs 255/65R18 (31.05 in)275/65R1731.07 in × 10.83 in255/65R1831.05 in × 10.04 in
Side profile and tread width, drawn to the same scale.
275/65R17 vs 255/65R18 differences
Measurement275/65R17255/65R18Difference% diff
Overall diameter31.07 in (789.3 mm)31.05 in (788.7 mm)−0.02 in (−0.6 mm)−0.08%
Sidewall height7.04 in (178.8 mm)6.53 in (165.8 mm)−0.51 in (−13.0 mm)−7.27%
Section width10.83 in (275.0 mm)10.04 in (255.0 mm)−0.79 in (−20.0 mm)−7.27%
Circumference97.62 in (2,479.7 mm)97.55 in (2,477.8 mm)−0.07 in (−1.9 mm)−0.08%
Revolutions per mile6496500+0.08%
True speed with the speedometer calibrated for 275/65R17
IndicatedActual on 275/65R17Actual on 255/65R18Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 255/65R18 lowers the vehicle by 0.01 in (0.3 mm) at the axle (half the −0.6 mm diameter difference).

255/65R18 is 0.02 in shorter than 275/65R17 and 20 mm narrower, a 0.08% difference in overall diameter.

With the speedometer calibrated for 275/65R17, an indicated 60 mph is actually 60.0 mph on 255/65R18, and revolutions per mile change from 649 to 650.

255/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 275/65R17.

Size pages

Other comparisons with 275/65R17

Other comparisons with 255/65R18

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.