265/55R20 vs 305/50R20

305/50R20 is 0.53 in (13.5 mm) taller than 265/55R20, a +1.69% diameter difference. With the speedometer set for 265/55R20, an indicated 60 mph is 61.0 mph on 305/50R20.

Is this a safe swap?

Diameter difference +1.69%: within the ±3% guideline

By overall diameter alone, 305/50R20 falls inside the ±3% range commonly used as a guideline when replacing 265/55R20. 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.

265/55R20 vs 305/50R20 differences
Measurement	265/55R20	305/50R20	Difference	% diff
Overall diameter	31.48 in (799.5 mm)	32.01 in (813.0 mm)	+0.53 in (+13.5 mm)	+1.69%
Sidewall height	5.74 in (145.8 mm)	6.00 in (152.5 mm)	+0.27 in (+6.8 mm)	+4.63%
Section width	10.43 in (265.0 mm)	12.01 in (305.0 mm)	+1.57 in (+40.0 mm)	+15.09%
Circumference	98.89 in (2,511.7 mm)	100.56 in (2,554.1 mm)	+1.67 in (+42.4 mm)	+1.69%
Revolutions per mile	641	630	−11	−1.66%

True speed with the speedometer calibrated for 265/55R20
Indicated	Actual on 265/55R20	Actual on 305/50R20	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.3 mph	+1.3 mph

Ride-height change: 305/50R20 raises the vehicle by 0.27 in (6.8 mm) at the axle (half the +13.5 mm diameter difference).

305/50R20 is 0.53 in taller than 265/55R20 and 40 mm wider, a 1.69% difference in overall diameter.

With the speedometer calibrated for 265/55R20, an indicated 60 mph is actually 61.0 mph on 305/50R20, and revolutions per mile change from 641 to 630.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 265/55R20

Other comparisons with 305/50R20

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