245/65R18 vs 265/50R20

265/50R20 is 0.11 in (2.7 mm) shorter than 245/65R18, a −0.35% diameter difference. With the speedometer set for 245/65R18, an indicated 60 mph is 59.8 mph on 265/50R20.

Is this a safe swap?

Diameter difference −0.35%: under 1%

By overall diameter alone, 265/50R20 is a near match for 245/65R18; 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.

245/65R18 vs 265/50R20 differences
Measurement	245/65R18	265/50R20	Difference	% diff
Overall diameter	30.54 in (775.7 mm)	30.43 in (773.0 mm)	−0.11 in (−2.7 mm)	−0.35%
Sidewall height	6.27 in (159.3 mm)	5.22 in (132.5 mm)	−1.05 in (−26.7 mm)	−16.80%
Section width	9.65 in (245.0 mm)	10.43 in (265.0 mm)	+0.79 in (+20.0 mm)	+8.16%
Circumference	95.94 in (2,436.9 mm)	95.61 in (2,428.5 mm)	−0.33 in (−8.5 mm)	−0.35%
Revolutions per mile	660	663	+2	+0.35%

True speed with the speedometer calibrated for 245/65R18
Indicated	Actual on 245/65R18	Actual on 265/50R20	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	74.7 mph	−0.3 mph

Ride-height change: 265/50R20 lowers the vehicle by 0.05 in (1.4 mm) at the axle (half the −2.7 mm diameter difference).

265/50R20 is 0.11 in shorter than 245/65R18 and 20 mm wider, a 0.35% difference in overall diameter.

With the speedometer calibrated for 245/65R18, an indicated 60 mph is actually 59.8 mph on 265/50R20, and revolutions per mile change from 660 to 663.

265/50R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 245/65R18.

Size pages

Other comparisons with 245/65R18

Other comparisons with 265/50R20

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