TireSizesFinder

275/65R18 vs 255/60R20

255/60R20 is 0.03 in (0.7 mm) shorter than 275/65R18, a −0.09% diameter difference. With the speedometer set for 275/65R18, an indicated 60 mph is 59.9 mph on 255/60R20.

Is this a safe swap?

Diameter difference −0.09%: under 1%

By overall diameter alone, 255/60R20 is a near match for 275/65R18; 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: 275/65R18 (32.07 in) vs 255/60R20 (32.05 in)275/65R1832.07 in × 10.83 in255/60R2032.05 in × 10.04 in
Side profile and tread width, drawn to the same scale.
275/65R18 vs 255/60R20 differences
Measurement275/65R18255/60R20Difference% diff
Overall diameter32.07 in (814.7 mm)32.05 in (814.0 mm)−0.03 in (−0.7 mm)−0.09%
Sidewall height7.04 in (178.8 mm)6.02 in (153.0 mm)−1.01 in (−25.7 mm)−14.41%
Section width10.83 in (275.0 mm)10.04 in (255.0 mm)−0.79 in (−20.0 mm)−7.27%
Circumference100.77 in (2,559.5 mm)100.68 in (2,557.3 mm)−0.09 in (−2.2 mm)−0.09%
Revolutions per mile629629+1+0.09%
True speed with the speedometer calibrated for 275/65R18
IndicatedActual on 275/65R18Actual on 255/60R20Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 255/60R20 lowers the vehicle by 0.01 in (0.4 mm) at the axle (half the −0.7 mm diameter difference).

255/60R20 is 0.03 in shorter than 275/65R18 and 20 mm narrower, a 0.09% difference in overall diameter.

With the speedometer calibrated for 275/65R18, an indicated 60 mph is actually 59.9 mph on 255/60R20, and revolutions per mile change from 629 to 629.

255/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 275/65R18.

Size pages

Other comparisons with 275/65R18

Other comparisons with 255/60R20

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