255/45R20 vs 295/40R20

295/40R20 is 0.26 in (6.5 mm) taller than 255/45R20, a +0.88% diameter difference. With the speedometer set for 255/45R20, an indicated 60 mph is 60.5 mph on 295/40R20.

Is this a safe swap?

Diameter difference +0.88%: under 1%

By overall diameter alone, 295/40R20 is a near match for 255/45R20; 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.

255/45R20 vs 295/40R20 differences
Measurement	255/45R20	295/40R20	Difference	% diff
Overall diameter	29.04 in (737.5 mm)	29.29 in (744.0 mm)	+0.26 in (+6.5 mm)	+0.88%
Sidewall height	4.52 in (114.8 mm)	4.65 in (118.0 mm)	+0.13 in (+3.3 mm)	+2.83%
Section width	10.04 in (255.0 mm)	11.61 in (295.0 mm)	+1.57 in (+40.0 mm)	+15.69%
Circumference	91.22 in (2,316.9 mm)	92.02 in (2,337.3 mm)	+0.80 in (+20.4 mm)	+0.88%
Revolutions per mile	695	689	−6	−0.87%

True speed with the speedometer calibrated for 255/45R20
Indicated	Actual on 255/45R20	Actual on 295/40R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 295/40R20 raises the vehicle by 0.13 in (3.3 mm) at the axle (half the +6.5 mm diameter difference).

295/40R20 is 0.26 in taller than 255/45R20 and 40 mm wider, a 0.88% difference in overall diameter.

With the speedometer calibrated for 255/45R20, an indicated 60 mph is actually 60.5 mph on 295/40R20, and revolutions per mile change from 695 to 689.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 255/45R20

Other comparisons with 295/40R20

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