TireSizesFinder

245/55R18 vs 265/40R20

265/40R20 is 0.26 in (6.7 mm) shorter than 245/55R18, a −0.92% diameter difference. With the speedometer set for 245/55R18, an indicated 60 mph is 59.4 mph on 265/40R20.

Is this a safe swap?

Diameter difference −0.92%: under 1%

By overall diameter alone, 265/40R20 is a near match for 245/55R18; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 245/55R18 (28.61 in) vs 265/40R20 (28.35 in)245/55R1828.61 in × 9.65 in265/40R2028.35 in × 10.43 in
Side profile and tread width, drawn to the same scale.
245/55R18 vs 265/40R20 differences
Measurement245/55R18265/40R20Difference% diff
Overall diameter28.61 in (726.7 mm)28.35 in (720.0 mm)−0.26 in (−6.7 mm)−0.92%
Sidewall height5.31 in (134.8 mm)4.17 in (106.0 mm)−1.13 in (−28.7 mm)−21.34%
Section width9.65 in (245.0 mm)10.43 in (265.0 mm)+0.79 in (+20.0 mm)+8.16%
Circumference89.88 in (2,283.0 mm)89.05 in (2,261.9 mm)−0.83 in (−21.0 mm)−0.92%
Revolutions per mile705711+7+0.93%
True speed with the speedometer calibrated for 245/55R18
IndicatedActual on 245/55R18Actual on 265/40R20Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.3 mph−0.7 mph

Ride-height change: 265/40R20 lowers the vehicle by 0.13 in (3.4 mm) at the axle (half the −6.7 mm diameter difference).

265/40R20 is 0.26 in shorter than 245/55R18 and 20 mm wider, a 0.92% difference in overall diameter.

With the speedometer calibrated for 245/55R18, an indicated 60 mph is actually 59.4 mph on 265/40R20, and revolutions per mile change from 705 to 711.

265/40R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 245/55R18.

Size pages

Other comparisons with 245/55R18

Other comparisons with 265/40R20

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.