TireSizesFinder

235/55R19 vs 285/40R20

285/40R20 is 0.20 in (5.1 mm) shorter than 235/55R19, a −0.69% diameter difference. With the speedometer set for 235/55R19, an indicated 60 mph is 59.6 mph on 285/40R20.

Is this a safe swap?

Diameter difference −0.69%: under 1%

By overall diameter alone, 285/40R20 is a near match for 235/55R19; 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: 235/55R19 (29.18 in) vs 285/40R20 (28.98 in)235/55R1929.18 in × 9.25 in285/40R2028.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
235/55R19 vs 285/40R20 differences
Measurement235/55R19285/40R20Difference% diff
Overall diameter29.18 in (741.1 mm)28.98 in (736.0 mm)−0.20 in (−5.1 mm)−0.69%
Sidewall height5.09 in (129.3 mm)4.49 in (114.0 mm)−0.60 in (−15.2 mm)−11.80%
Section width9.25 in (235.0 mm)11.22 in (285.0 mm)+1.97 in (+50.0 mm)+21.28%
Circumference91.66 in (2,328.2 mm)91.03 in (2,312.2 mm)−0.63 in (−16.0 mm)−0.69%
Revolutions per mile691696+5+0.69%
True speed with the speedometer calibrated for 235/55R19
IndicatedActual on 235/55R19Actual on 285/40R20Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.6 mph−0.4 mph
75 mph75.0 mph74.5 mph−0.5 mph

Ride-height change: 285/40R20 lowers the vehicle by 0.10 in (2.5 mm) at the axle (half the −5.1 mm diameter difference).

285/40R20 is 0.20 in shorter than 235/55R19 and 50 mm wider, a 0.69% difference in overall diameter.

With the speedometer calibrated for 235/55R19, an indicated 60 mph is actually 59.6 mph on 285/40R20, and revolutions per mile change from 691 to 696.

285/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 235/55R19.

Size pages

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