265/65R18 vs 265/55R20

265/55R20 is 0.09 in (2.2 mm) shorter than 265/65R18, a −0.27% diameter difference. With the speedometer set for 265/65R18, an indicated 60 mph is 59.8 mph on 265/55R20.

Is this a safe swap?

Diameter difference −0.27%: under 1%

By overall diameter alone, 265/55R20 is a near match for 265/65R18; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

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

265/65R18 vs 265/55R20 differences
Measurement	265/65R18	265/55R20	Difference	% diff
Overall diameter	31.56 in (801.7 mm)	31.48 in (799.5 mm)	−0.09 in (−2.2 mm)	−0.27%
Sidewall height	6.78 in (172.3 mm)	5.74 in (145.8 mm)	−1.04 in (−26.5 mm)	−15.38%
Section width	10.43 in (265.0 mm)	10.43 in (265.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	99.16 in (2,518.6 mm)	98.89 in (2,511.7 mm)	−0.27 in (−6.9 mm)	−0.27%
Revolutions per mile	639	641	+2	+0.28%

True speed with the speedometer calibrated for 265/65R18
Indicated	Actual on 265/65R18	Actual on 265/55R20	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.8 mph	−0.2 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 265/55R20 lowers the vehicle by 0.04 in (1.1 mm) at the axle (half the −2.2 mm diameter difference).

265/55R20 is 0.09 in shorter than 265/65R18 and the same width, a 0.27% difference in overall diameter.

With the speedometer calibrated for 265/65R18, an indicated 60 mph is actually 59.8 mph on 265/55R20, and revolutions per mile change from 639 to 641.

265/55R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/65R18.

Size pages

Other comparisons with 265/65R18

Other comparisons with 265/55R20

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