245/40R20 vs 265/40R20

265/40R20 is 0.63 in (16.0 mm) taller than 245/40R20, a +2.27% diameter difference. With the speedometer set for 245/40R20, an indicated 60 mph is 61.4 mph on 265/40R20.

Is this a safe swap?

Diameter difference +2.27%: within the ±3% guideline

By overall diameter alone, 265/40R20 falls inside the ±3% range commonly used as a guideline when replacing 245/40R20. 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.

245/40R20 vs 265/40R20 differences
Measurement	245/40R20	265/40R20	Difference	% diff
Overall diameter	27.72 in (704.0 mm)	28.35 in (720.0 mm)	+0.63 in (+16.0 mm)	+2.27%
Sidewall height	3.86 in (98.0 mm)	4.17 in (106.0 mm)	+0.31 in (+8.0 mm)	+8.16%
Section width	9.65 in (245.0 mm)	10.43 in (265.0 mm)	+0.79 in (+20.0 mm)	+8.16%
Circumference	87.07 in (2,211.7 mm)	89.05 in (2,261.9 mm)	+1.98 in (+50.3 mm)	+2.27%
Revolutions per mile	728	711	−16	−2.22%

True speed with the speedometer calibrated for 245/40R20
Indicated	Actual on 245/40R20	Actual on 265/40R20	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: 265/40R20 raises the vehicle by 0.31 in (8.0 mm) at the axle (half the +16.0 mm diameter difference).

265/40R20 is 0.63 in taller than 245/40R20 and 20 mm wider, a 2.27% difference in overall diameter.

With the speedometer calibrated for 245/40R20, an indicated 60 mph is actually 61.4 mph on 265/40R20, and revolutions per mile change from 728 to 711.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 245/40R20

Other comparisons with 265/40R20

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