TireSizesFinder

255/40R21 vs 285/30R22

285/30R22 is 0.30 in (7.6 mm) shorter than 255/40R21, a −1.03% diameter difference. With the speedometer set for 255/40R21, an indicated 60 mph is 59.4 mph on 285/30R22.

Is this a safe swap?

Diameter difference −1.03%: within the ±3% guideline

By overall diameter alone, 285/30R22 falls inside the ±3% range commonly used as a guideline when replacing 255/40R21. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/40R21 (29.03 in) vs 285/30R22 (28.73 in)255/40R2129.03 in × 10.04 in285/30R2228.73 in × 11.22 in
Side profile and tread width, drawn to the same scale.
255/40R21 vs 285/30R22 differences
Measurement255/40R21285/30R22Difference% diff
Overall diameter29.03 in (737.4 mm)28.73 in (729.8 mm)−0.30 in (−7.6 mm)−1.03%
Sidewall height4.02 in (102.0 mm)3.37 in (85.5 mm)−0.65 in (−16.5 mm)−16.18%
Section width10.04 in (255.0 mm)11.22 in (285.0 mm)+1.18 in (+30.0 mm)+11.76%
Circumference91.21 in (2,316.6 mm)90.27 in (2,292.7 mm)−0.94 in (−23.9 mm)−1.03%
Revolutions per mile695702+7+1.04%
True speed with the speedometer calibrated for 255/40R21
IndicatedActual on 255/40R21Actual on 285/30R22Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.2 mph−0.8 mph

Ride-height change: 285/30R22 lowers the vehicle by 0.15 in (3.8 mm) at the axle (half the −7.6 mm diameter difference).

285/30R22 is 0.30 in shorter than 255/40R21 and 30 mm wider, a 1.03% difference in overall diameter.

With the speedometer calibrated for 255/40R21, an indicated 60 mph is actually 59.4 mph on 285/30R22, and revolutions per mile change from 695 to 702.

285/30R22 mounts on a 22-inch wheel, a plus-1 fitment from the 21-inch wheel of 255/40R21.

Size pages

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