265/65R18 vs 275/55R20

275/55R20 is 0.35 in (8.8 mm) taller than 265/65R18, a +1.10% diameter difference. With the speedometer set for 265/65R18, an indicated 60 mph is 60.7 mph on 275/55R20.

Is this a safe swap?

Diameter difference +1.10%: within the ±3% guideline

By overall diameter alone, 275/55R20 falls inside the ±3% range commonly used as a guideline when replacing 265/65R18. 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 275/55R20 differences
Measurement	265/65R18	275/55R20	Difference	% diff
Overall diameter	31.56 in (801.7 mm)	31.91 in (810.5 mm)	+0.35 in (+8.8 mm)	+1.10%
Sidewall height	6.78 in (172.3 mm)	5.95 in (151.3 mm)	−0.83 in (−21.0 mm)	−12.19%
Section width	10.43 in (265.0 mm)	10.83 in (275.0 mm)	+0.39 in (+10.0 mm)	+3.77%
Circumference	99.16 in (2,518.6 mm)	100.25 in (2,546.3 mm)	+1.09 in (+27.6 mm)	+1.10%
Revolutions per mile	639	632	−7	−1.09%

True speed with the speedometer calibrated for 265/65R18
Indicated	Actual on 265/65R18	Actual on 275/55R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 275/55R20 raises the vehicle by 0.17 in (4.4 mm) at the axle (half the +8.8 mm diameter difference).

275/55R20 is 0.35 in taller than 265/65R18 and 10 mm wider, a 1.10% difference in overall diameter.

With the speedometer calibrated for 265/65R18, an indicated 60 mph is actually 60.7 mph on 275/55R20, and revolutions per mile change from 639 to 632.

275/55R20 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 275/55R20

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