TireSizesFinder

305/30R21 vs 255/30R22

255/30R22 is 0.18 in (4.6 mm) shorter than 305/30R21, a −0.64% diameter difference. With the speedometer set for 305/30R21, an indicated 60 mph is 59.6 mph on 255/30R22.

Is this a safe swap?

Diameter difference −0.64%: under 1%

By overall diameter alone, 255/30R22 is a near match for 305/30R21; 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: 305/30R21 (28.20 in) vs 255/30R22 (28.02 in)305/30R2128.20 in × 12.01 in255/30R2228.02 in × 10.04 in
Side profile and tread width, drawn to the same scale.
305/30R21 vs 255/30R22 differences
Measurement305/30R21255/30R22Difference% diff
Overall diameter28.20 in (716.4 mm)28.02 in (711.8 mm)−0.18 in (−4.6 mm)−0.64%
Sidewall height3.60 in (91.5 mm)3.01 in (76.5 mm)−0.59 in (−15.0 mm)−16.39%
Section width12.01 in (305.0 mm)10.04 in (255.0 mm)−1.97 in (−50.0 mm)−16.39%
Circumference88.61 in (2,250.6 mm)88.04 in (2,236.2 mm)−0.57 in (−14.5 mm)−0.64%
Revolutions per mile715720+5+0.65%
True speed with the speedometer calibrated for 305/30R21
IndicatedActual on 305/30R21Actual on 255/30R22Difference
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: 255/30R22 lowers the vehicle by 0.09 in (2.3 mm) at the axle (half the −4.6 mm diameter difference).

255/30R22 is 0.18 in shorter than 305/30R21 and 50 mm narrower, a 0.64% difference in overall diameter.

With the speedometer calibrated for 305/30R21, an indicated 60 mph is actually 59.6 mph on 255/30R22, and revolutions per mile change from 715 to 720.

255/30R22 mounts on a 22-inch wheel, a plus-1 fitment from the 21-inch wheel of 305/30R21.

Size pages

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