TireSizesFinder

225/55R17 vs 275/40R18

275/40R18 is 0.08 in (2.1 mm) shorter than 225/55R17, a −0.31% diameter difference. With the speedometer set for 225/55R17, an indicated 60 mph is 59.8 mph on 275/40R18.

Is this a safe swap?

Diameter difference −0.31%: under 1%

By overall diameter alone, 275/40R18 is a near match for 225/55R17; 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: 225/55R17 (26.74 in) vs 275/40R18 (26.66 in)225/55R1726.74 in × 8.86 in275/40R1826.66 in × 10.83 in
Side profile and tread width, drawn to the same scale.
225/55R17 vs 275/40R18 differences
Measurement225/55R17275/40R18Difference% diff
Overall diameter26.74 in (679.3 mm)26.66 in (677.2 mm)−0.08 in (−2.1 mm)−0.31%
Sidewall height4.87 in (123.8 mm)4.33 in (110.0 mm)−0.54 in (−13.7 mm)−11.11%
Section width8.86 in (225.0 mm)10.83 in (275.0 mm)+1.97 in (+50.0 mm)+22.22%
Circumference84.02 in (2,134.1 mm)83.76 in (2,127.5 mm)−0.26 in (−6.6 mm)−0.31%
Revolutions per mile754756+2+0.31%
True speed with the speedometer calibrated for 225/55R17
IndicatedActual on 225/55R17Actual on 275/40R18Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 275/40R18 lowers the vehicle by 0.04 in (1.0 mm) at the axle (half the −2.1 mm diameter difference).

275/40R18 is 0.08 in shorter than 225/55R17 and 50 mm wider, a 0.31% difference in overall diameter.

With the speedometer calibrated for 225/55R17, an indicated 60 mph is actually 59.8 mph on 275/40R18, and revolutions per mile change from 754 to 756.

275/40R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/55R17.

Size pages

Other comparisons with 225/55R17

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