275/55R20 vs 305/50R20

305/50R20 is 0.10 in (2.5 mm) taller than 275/55R20, a +0.31% diameter difference. With the speedometer set for 275/55R20, an indicated 60 mph is 60.2 mph on 305/50R20.

Is this a safe swap?

Diameter difference +0.31%: under 1%

By overall diameter alone, 305/50R20 is a near match for 275/55R20; 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.

275/55R20 vs 305/50R20 differences
Measurement	275/55R20	305/50R20	Difference	% diff
Overall diameter	31.91 in (810.5 mm)	32.01 in (813.0 mm)	+0.10 in (+2.5 mm)	+0.31%
Sidewall height	5.95 in (151.3 mm)	6.00 in (152.5 mm)	+0.05 in (+1.3 mm)	+0.83%
Section width	10.83 in (275.0 mm)	12.01 in (305.0 mm)	+1.18 in (+30.0 mm)	+10.91%
Circumference	100.25 in (2,546.3 mm)	100.56 in (2,554.1 mm)	+0.31 in (+7.9 mm)	+0.31%
Revolutions per mile	632	630	−2	−0.31%

True speed with the speedometer calibrated for 275/55R20
Indicated	Actual on 275/55R20	Actual on 305/50R20	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: 305/50R20 raises the vehicle by 0.05 in (1.3 mm) at the axle (half the +2.5 mm diameter difference).

305/50R20 is 0.10 in taller than 275/55R20 and 30 mm wider, a 0.31% difference in overall diameter.

With the speedometer calibrated for 275/55R20, an indicated 60 mph is actually 60.2 mph on 305/50R20, and revolutions per mile change from 632 to 630.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 275/55R20

Other comparisons with 305/50R20

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