265/70R18 vs 255/60R20

255/60R20 is 0.56 in (14.2 mm) shorter than 265/70R18, a −1.71% diameter difference. With the speedometer set for 265/70R18, an indicated 60 mph is 59.0 mph on 255/60R20.

Is this a safe swap?

Diameter difference −1.71%: within the ±3% guideline

By overall diameter alone, 255/60R20 falls inside the ±3% range commonly used as a guideline when replacing 265/70R18. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

265/70R18 vs 255/60R20 differences
Measurement	265/70R18	255/60R20	Difference	% diff
Overall diameter	32.61 in (828.2 mm)	32.05 in (814.0 mm)	−0.56 in (−14.2 mm)	−1.71%
Sidewall height	7.30 in (185.5 mm)	6.02 in (153.0 mm)	−1.28 in (−32.5 mm)	−17.52%
Section width	10.43 in (265.0 mm)	10.04 in (255.0 mm)	−0.39 in (−10.0 mm)	−3.77%
Circumference	102.44 in (2,601.9 mm)	100.68 in (2,557.3 mm)	−1.76 in (−44.6 mm)	−1.71%
Revolutions per mile	619	629	+11	+1.74%

True speed with the speedometer calibrated for 265/70R18
Indicated	Actual on 265/70R18	Actual on 255/60R20	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.0 mph	−1.0 mph
75 mph	75.0 mph	73.7 mph	−1.3 mph

Ride-height change: 255/60R20 lowers the vehicle by 0.28 in (7.1 mm) at the axle (half the −14.2 mm diameter difference).

255/60R20 is 0.56 in shorter than 265/70R18 and 10 mm narrower, a 1.71% difference in overall diameter.

With the speedometer calibrated for 265/70R18, an indicated 60 mph is actually 59.0 mph on 255/60R20, and revolutions per mile change from 619 to 629.

255/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/70R18.

Size pages

Other comparisons with 265/70R18

Other comparisons with 255/60R20

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.