295/55R20 vs 305/55R20

305/55R20 is 0.43 in (11.0 mm) taller than 295/55R20, a +1.32% diameter difference. With the speedometer set for 295/55R20, an indicated 60 mph is 60.8 mph on 305/55R20.

Is this a safe swap?

Diameter difference +1.32%: within the ±3% guideline

By overall diameter alone, 305/55R20 falls inside the ±3% range commonly used as a guideline when replacing 295/55R20. 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.

295/55R20 vs 305/55R20 differences
Measurement	295/55R20	305/55R20	Difference	% diff
Overall diameter	32.78 in (832.5 mm)	33.21 in (843.5 mm)	+0.43 in (+11.0 mm)	+1.32%
Sidewall height	6.39 in (162.3 mm)	6.60 in (167.8 mm)	+0.22 in (+5.5 mm)	+3.39%
Section width	11.61 in (295.0 mm)	12.01 in (305.0 mm)	+0.39 in (+10.0 mm)	+3.39%
Circumference	102.97 in (2,615.4 mm)	104.33 in (2,649.9 mm)	+1.36 in (+34.6 mm)	+1.32%
Revolutions per mile	615	607	−8	−1.30%

True speed with the speedometer calibrated for 295/55R20
Indicated	Actual on 295/55R20	Actual on 305/55R20	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 305/55R20 raises the vehicle by 0.22 in (5.5 mm) at the axle (half the +11.0 mm diameter difference).

305/55R20 is 0.43 in taller than 295/55R20 and 10 mm wider, a 1.32% difference in overall diameter.

With the speedometer calibrated for 295/55R20, an indicated 60 mph is actually 60.8 mph on 305/55R20, and revolutions per mile change from 615 to 607.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 295/55R20

Other comparisons with 305/55R20

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