TireSizesFinder

285/40R19 vs 245/40R20

245/40R20 is 0.26 in (6.6 mm) shorter than 285/40R19, a −0.93% diameter difference. With the speedometer set for 285/40R19, an indicated 60 mph is 59.4 mph on 245/40R20.

Is this a safe swap?

Diameter difference −0.93%: under 1%

By overall diameter alone, 245/40R20 is a near match for 285/40R19; 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: 285/40R19 (27.98 in) vs 245/40R20 (27.72 in)285/40R1927.98 in × 11.22 in245/40R2027.72 in × 9.65 in
Side profile and tread width, drawn to the same scale.
285/40R19 vs 245/40R20 differences
Measurement285/40R19245/40R20Difference% diff
Overall diameter27.98 in (710.6 mm)27.72 in (704.0 mm)−0.26 in (−6.6 mm)−0.93%
Sidewall height4.49 in (114.0 mm)3.86 in (98.0 mm)−0.63 in (−16.0 mm)−14.04%
Section width11.22 in (285.0 mm)9.65 in (245.0 mm)−1.57 in (−40.0 mm)−14.04%
Circumference87.89 in (2,232.4 mm)87.07 in (2,211.7 mm)−0.82 in (−20.7 mm)−0.93%
Revolutions per mile721728+7+0.94%
True speed with the speedometer calibrated for 285/40R19
IndicatedActual on 285/40R19Actual on 245/40R20Difference
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: 245/40R20 lowers the vehicle by 0.13 in (3.3 mm) at the axle (half the −6.6 mm diameter difference).

245/40R20 is 0.26 in shorter than 285/40R19 and 40 mm narrower, a 0.93% difference in overall diameter.

With the speedometer calibrated for 285/40R19, an indicated 60 mph is actually 59.4 mph on 245/40R20, and revolutions per mile change from 721 to 728.

245/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 285/40R19.

Size pages

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