TireSizesFinder

235/55R18 vs 285/40R19

285/40R19 is 0.20 in (5.1 mm) shorter than 235/55R18, a −0.71% diameter difference. With the speedometer set for 235/55R18, an indicated 60 mph is 59.6 mph on 285/40R19.

Is this a safe swap?

Diameter difference −0.71%: under 1%

By overall diameter alone, 285/40R19 is a near match for 235/55R18; 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: 235/55R18 (28.18 in) vs 285/40R19 (27.98 in)235/55R1828.18 in × 9.25 in285/40R1927.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
235/55R18 vs 285/40R19 differences
Measurement235/55R18285/40R19Difference% diff
Overall diameter28.18 in (715.7 mm)27.98 in (710.6 mm)−0.20 in (−5.1 mm)−0.71%
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%
Circumference88.52 in (2,248.4 mm)87.89 in (2,232.4 mm)−0.63 in (−16.0 mm)−0.71%
Revolutions per mile716721+5+0.72%
True speed with the speedometer calibrated for 235/55R18
IndicatedActual on 235/55R18Actual on 285/40R19Difference
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: 285/40R19 lowers the vehicle by 0.10 in (2.6 mm) at the axle (half the −5.1 mm diameter difference).

285/40R19 is 0.20 in shorter than 235/55R18 and 50 mm wider, a 0.71% difference in overall diameter.

With the speedometer calibrated for 235/55R18, an indicated 60 mph is actually 59.6 mph on 285/40R19, and revolutions per mile change from 716 to 721.

285/40R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 235/55R18.

Size pages

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