265/60R18 vs 245/55R20

245/55R20 is 0.09 in (2.3 mm) taller than 265/60R18, a +0.30% diameter difference. With the speedometer set for 265/60R18, an indicated 60 mph is 60.2 mph on 245/55R20.

Is this a safe swap?

Diameter difference +0.30%: under 1%

By overall diameter alone, 245/55R20 is a near match for 265/60R18; 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.

265/60R18 vs 245/55R20 differences
Measurement	265/60R18	245/55R20	Difference	% diff
Overall diameter	30.52 in (775.2 mm)	30.61 in (777.5 mm)	+0.09 in (+2.3 mm)	+0.30%
Sidewall height	6.26 in (159.0 mm)	5.31 in (134.8 mm)	−0.95 in (−24.2 mm)	−15.25%
Section width	10.43 in (265.0 mm)	9.65 in (245.0 mm)	−0.79 in (−20.0 mm)	−7.55%
Circumference	95.88 in (2,435.4 mm)	96.16 in (2,442.6 mm)	+0.28 in (+7.2 mm)	+0.30%
Revolutions per mile	661	659	−2	−0.30%

True speed with the speedometer calibrated for 265/60R18
Indicated	Actual on 265/60R18	Actual on 245/55R20	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 245/55R20 raises the vehicle by 0.05 in (1.1 mm) at the axle (half the +2.3 mm diameter difference).

245/55R20 is 0.09 in taller than 265/60R18 and 20 mm narrower, a 0.30% difference in overall diameter.

With the speedometer calibrated for 265/60R18, an indicated 60 mph is actually 60.2 mph on 245/55R20, and revolutions per mile change from 661 to 659.

245/55R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/60R18.

Size pages

Other comparisons with 265/60R18

Other comparisons with 245/55R20

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