295/45R20 vs 305/45R20

305/45R20 is 0.35 in (9.0 mm) taller than 295/45R20, a +1.16% diameter difference. With the speedometer set for 295/45R20, an indicated 60 mph is 60.7 mph on 305/45R20.

Is this a safe swap?

Diameter difference +1.16%: within the ±3% guideline

By overall diameter alone, 305/45R20 falls inside the ±3% range commonly used as a guideline when replacing 295/45R20. 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.

295/45R20 vs 305/45R20 differences
Measurement	295/45R20	305/45R20	Difference	% diff
Overall diameter	30.45 in (773.5 mm)	30.81 in (782.5 mm)	+0.35 in (+9.0 mm)	+1.16%
Sidewall height	5.23 in (132.8 mm)	5.40 in (137.3 mm)	+0.18 in (+4.5 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	95.67 in (2,430.0 mm)	96.78 in (2,458.3 mm)	+1.11 in (+28.3 mm)	+1.16%
Revolutions per mile	662	655	−8	−1.15%

True speed with the speedometer calibrated for 295/45R20
Indicated	Actual on 295/45R20	Actual on 305/45R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 305/45R20 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

305/45R20 is 0.35 in taller than 295/45R20 and 10 mm wider, a 1.16% difference in overall diameter.

With the speedometer calibrated for 295/45R20, an indicated 60 mph is actually 60.7 mph on 305/45R20, and revolutions per mile change from 662 to 655.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 295/45R20

Other comparisons with 305/45R20

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