225/40R20 vs 245/40R20

245/40R20 is 0.63 in (16.0 mm) taller than 225/40R20, a +2.33% diameter difference. With the speedometer set for 225/40R20, an indicated 60 mph is 61.4 mph on 245/40R20.

Is this a safe swap?

Diameter difference +2.33%: within the ±3% guideline

By overall diameter alone, 245/40R20 falls inside the ±3% range commonly used as a guideline when replacing 225/40R20. 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.

225/40R20 vs 245/40R20 differences
Measurement	225/40R20	245/40R20	Difference	% diff
Overall diameter	27.09 in (688.0 mm)	27.72 in (704.0 mm)	+0.63 in (+16.0 mm)	+2.33%
Sidewall height	3.54 in (90.0 mm)	3.86 in (98.0 mm)	+0.31 in (+8.0 mm)	+8.89%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	85.10 in (2,161.4 mm)	87.07 in (2,211.7 mm)	+1.98 in (+50.3 mm)	+2.33%
Revolutions per mile	745	728	−17	−2.27%

True speed with the speedometer calibrated for 225/40R20
Indicated	Actual on 225/40R20	Actual on 245/40R20	Difference
30 mph	30.0 mph	30.7 mph	+0.7 mph
60 mph	60.0 mph	61.4 mph	+1.4 mph
75 mph	75.0 mph	76.7 mph	+1.7 mph

Ride-height change: 245/40R20 raises the vehicle by 0.31 in (8.0 mm) at the axle (half the +16.0 mm diameter difference).

245/40R20 is 0.63 in taller than 225/40R20 and 20 mm wider, a 2.33% difference in overall diameter.

With the speedometer calibrated for 225/40R20, an indicated 60 mph is actually 61.4 mph on 245/40R20, and revolutions per mile change from 745 to 728.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 225/40R20

Other comparisons with 245/40R20

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