265/60R20 vs 305/55R20

305/55R20 is 0.69 in (17.5 mm) taller than 265/60R20, a +2.12% diameter difference. With the speedometer set for 265/60R20, an indicated 60 mph is 61.3 mph on 305/55R20.

Is this a safe swap?

Diameter difference +2.12%: within the ±3% guideline

By overall diameter alone, 305/55R20 falls inside the ±3% range commonly used as a guideline when replacing 265/60R20. 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.

265/60R20 vs 305/55R20 differences
Measurement	265/60R20	305/55R20	Difference	% diff
Overall diameter	32.52 in (826.0 mm)	33.21 in (843.5 mm)	+0.69 in (+17.5 mm)	+2.12%
Sidewall height	6.26 in (159.0 mm)	6.60 in (167.8 mm)	+0.34 in (+8.8 mm)	+5.50%
Section width	10.43 in (265.0 mm)	12.01 in (305.0 mm)	+1.57 in (+40.0 mm)	+15.09%
Circumference	102.16 in (2,595.0 mm)	104.33 in (2,649.9 mm)	+2.16 in (+55.0 mm)	+2.12%
Revolutions per mile	620	607	−13	−2.07%

True speed with the speedometer calibrated for 265/60R20
Indicated	Actual on 265/60R20	Actual on 305/55R20	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.3 mph	+1.3 mph
75 mph	75.0 mph	76.6 mph	+1.6 mph

Ride-height change: 305/55R20 raises the vehicle by 0.34 in (8.8 mm) at the axle (half the +17.5 mm diameter difference).

305/55R20 is 0.69 in taller than 265/60R20 and 40 mm wider, a 2.12% difference in overall diameter.

With the speedometer calibrated for 265/60R20, an indicated 60 mph is actually 61.3 mph on 305/55R20, and revolutions per mile change from 620 to 607.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 265/60R20

Other comparisons with 305/55R20

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