TireSizesFinder

205/75R16 vs 225/55R18

225/55R18 is 0.36 in (9.2 mm) shorter than 205/75R16, a −1.29% diameter difference. With the speedometer set for 205/75R16, an indicated 60 mph is 59.2 mph on 225/55R18.

Is this a safe swap?

Diameter difference −1.29%: within the ±3% guideline

By overall diameter alone, 225/55R18 falls inside the ±3% range commonly used as a guideline when replacing 205/75R16. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 205/75R16 (28.11 in) vs 225/55R18 (27.74 in)205/75R1628.11 in × 8.07 in225/55R1827.74 in × 8.86 in
Side profile and tread width, drawn to the same scale.
205/75R16 vs 225/55R18 differences
Measurement205/75R16225/55R18Difference% diff
Overall diameter28.11 in (713.9 mm)27.74 in (704.7 mm)−0.36 in (−9.2 mm)−1.29%
Sidewall height6.05 in (153.8 mm)4.87 in (123.8 mm)−1.18 in (−30.0 mm)−19.51%
Section width8.07 in (205.0 mm)8.86 in (225.0 mm)+0.79 in (+20.0 mm)+9.76%
Circumference88.30 in (2,242.8 mm)87.16 in (2,213.9 mm)−1.14 in (−28.9 mm)−1.29%
Revolutions per mile718727+9+1.31%
True speed with the speedometer calibrated for 205/75R16
IndicatedActual on 205/75R16Actual on 225/55R18Difference
30 mph30.0 mph29.6 mph−0.4 mph
60 mph60.0 mph59.2 mph−0.8 mph
75 mph75.0 mph74.0 mph−1.0 mph

Ride-height change: 225/55R18 lowers the vehicle by 0.18 in (4.6 mm) at the axle (half the −9.2 mm diameter difference).

225/55R18 is 0.36 in shorter than 205/75R16 and 20 mm wider, a 1.29% difference in overall diameter.

With the speedometer calibrated for 205/75R16, an indicated 60 mph is actually 59.2 mph on 225/55R18, and revolutions per mile change from 718 to 727.

225/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 205/75R16.

Size pages

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