TireSizesFinder

285/45R19 vs 285/40R20

285/40R20 is 0.12 in (3.1 mm) shorter than 285/45R19, a −0.42% diameter difference. With the speedometer set for 285/45R19, an indicated 60 mph is 59.7 mph on 285/40R20.

Is this a safe swap?

Diameter difference −0.42%: under 1%

By overall diameter alone, 285/40R20 is a near match for 285/45R19; 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: 285/45R19 (29.10 in) vs 285/40R20 (28.98 in)285/45R1929.10 in × 11.22 in285/40R2028.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
285/45R19 vs 285/40R20 differences
Measurement285/45R19285/40R20Difference% diff
Overall diameter29.10 in (739.1 mm)28.98 in (736.0 mm)−0.12 in (−3.1 mm)−0.42%
Sidewall height5.05 in (128.3 mm)4.49 in (114.0 mm)−0.56 in (−14.2 mm)−11.11%
Section width11.22 in (285.0 mm)11.22 in (285.0 mm)0.00 in (0.0 mm)0.00%
Circumference91.42 in (2,322.0 mm)91.03 in (2,312.2 mm)−0.38 in (−9.7 mm)−0.42%
Revolutions per mile693696+3+0.42%
True speed with the speedometer calibrated for 285/45R19
IndicatedActual on 285/45R19Actual on 285/40R20Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.7 mph−0.3 mph
75 mph75.0 mph74.7 mph−0.3 mph

Ride-height change: 285/40R20 lowers the vehicle by 0.06 in (1.5 mm) at the axle (half the −3.1 mm diameter difference).

285/40R20 is 0.12 in shorter than 285/45R19 and the same width, a 0.42% difference in overall diameter.

With the speedometer calibrated for 285/45R19, an indicated 60 mph is actually 59.7 mph on 285/40R20, and revolutions per mile change from 693 to 696.

285/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 285/45R19.

Size pages

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