245/65R18 vs 275/50R20

275/50R20 is 0.29 in (7.3 mm) taller than 245/65R18, a +0.94% diameter difference. With the speedometer set for 245/65R18, an indicated 60 mph is 60.6 mph on 275/50R20.

Is this a safe swap?

Diameter difference +0.94%: under 1%

By overall diameter alone, 275/50R20 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 275/50R20 differences
Measurement	245/65R18	275/50R20	Difference	% diff
Overall diameter	30.54 in (775.7 mm)	30.83 in (783.0 mm)	+0.29 in (+7.3 mm)	+0.94%
Sidewall height	6.27 in (159.3 mm)	5.41 in (137.5 mm)	−0.86 in (−21.7 mm)	−13.66%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	95.94 in (2,436.9 mm)	96.85 in (2,459.9 mm)	+0.90 in (+22.9 mm)	+0.94%
Revolutions per mile	660	654	−6	−0.93%

True speed with the speedometer calibrated for 245/65R18
Indicated	Actual on 245/65R18	Actual on 275/50R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 275/50R20 raises the vehicle by 0.14 in (3.6 mm) at the axle (half the +7.3 mm diameter difference).

275/50R20 is 0.29 in taller than 245/65R18 and 30 mm wider, a 0.94% difference in overall diameter.

With the speedometer calibrated for 245/65R18, an indicated 60 mph is actually 60.6 mph on 275/50R20, and revolutions per mile change from 660 to 654.

275/50R20 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 275/50R20

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