305/45R20 vs 275/50R20

275/50R20 is 0.02 in (0.5 mm) taller than 305/45R20, a +0.06% diameter difference. With the speedometer set for 305/45R20, an indicated 60 mph is 60.0 mph on 275/50R20.

Is this a safe swap?

Diameter difference +0.06%: under 1%

By overall diameter alone, 275/50R20 is a near match for 305/45R20; 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.

305/45R20 vs 275/50R20 differences
Measurement	305/45R20	275/50R20	Difference	% diff
Overall diameter	30.81 in (782.5 mm)	30.83 in (783.0 mm)	+0.02 in (+0.5 mm)	+0.06%
Sidewall height	5.40 in (137.3 mm)	5.41 in (137.5 mm)	+0.01 in (+0.3 mm)	+0.18%
Section width	12.01 in (305.0 mm)	10.83 in (275.0 mm)	−1.18 in (−30.0 mm)	−9.84%
Circumference	96.78 in (2,458.3 mm)	96.85 in (2,459.9 mm)	+0.06 in (+1.6 mm)	+0.06%
Revolutions per mile	655	654	0	−0.06%

True speed with the speedometer calibrated for 305/45R20
Indicated	Actual on 305/45R20	Actual on 275/50R20
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 275/50R20 raises the vehicle by 0.01 in (0.3 mm) at the axle (half the +0.5 mm diameter difference).

275/50R20 is 0.02 in taller than 305/45R20 and 30 mm narrower, a 0.06% difference in overall diameter.

With the speedometer calibrated for 305/45R20, an indicated 60 mph is actually 60.0 mph on 275/50R20, and revolutions per mile change from 655 to 654.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 305/45R20

Other comparisons with 275/50R20

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