TireSizesFinder

285/45R19 vs 255/40R21

255/40R21 is 0.07 in (1.7 mm) shorter than 285/45R19, a −0.23% diameter difference. With the speedometer set for 285/45R19, an indicated 60 mph is 59.9 mph on 255/40R21.

Is this a safe swap?

Diameter difference −0.23%: under 1%

By overall diameter alone, 255/40R21 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 255/40R21 (29.03 in)285/45R1929.10 in × 11.22 in255/40R2129.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
285/45R19 vs 255/40R21 differences
Measurement285/45R19255/40R21Difference% diff
Overall diameter29.10 in (739.1 mm)29.03 in (737.4 mm)−0.07 in (−1.7 mm)−0.23%
Sidewall height5.05 in (128.3 mm)4.02 in (102.0 mm)−1.03 in (−26.2 mm)−20.47%
Section width11.22 in (285.0 mm)10.04 in (255.0 mm)−1.18 in (−30.0 mm)−10.53%
Circumference91.42 in (2,322.0 mm)91.21 in (2,316.6 mm)−0.21 in (−5.3 mm)−0.23%
Revolutions per mile693695+2+0.23%
True speed with the speedometer calibrated for 285/45R19
IndicatedActual on 285/45R19Actual on 255/40R21Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 255/40R21 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.7 mm diameter difference).

255/40R21 is 0.07 in shorter than 285/45R19 and 30 mm narrower, a 0.23% difference in overall diameter.

With the speedometer calibrated for 285/45R19, an indicated 60 mph is actually 59.9 mph on 255/40R21, and revolutions per mile change from 693 to 695.

255/40R21 mounts on a 21-inch wheel, a plus-2 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.