TireSizesFinder

275/40R17 vs 215/45R18

215/45R18 is 0.04 in (1.1 mm) shorter than 275/40R17, a −0.17% diameter difference. With the speedometer set for 275/40R17, an indicated 60 mph is 59.9 mph on 215/45R18.

Is this a safe swap?

Diameter difference −0.17%: under 1%

By overall diameter alone, 215/45R18 is a near match for 275/40R17; 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: 275/40R17 (25.66 in) vs 215/45R18 (25.62 in)275/40R1725.66 in × 10.83 in215/45R1825.62 in × 8.46 in
Side profile and tread width, drawn to the same scale.
275/40R17 vs 215/45R18 differences
Measurement275/40R17215/45R18Difference% diff
Overall diameter25.66 in (651.8 mm)25.62 in (650.7 mm)−0.04 in (−1.1 mm)−0.17%
Sidewall height4.33 in (110.0 mm)3.81 in (96.8 mm)−0.52 in (−13.2 mm)−12.05%
Section width10.83 in (275.0 mm)8.46 in (215.0 mm)−2.36 in (−60.0 mm)−21.82%
Circumference80.62 in (2,047.7 mm)80.48 in (2,044.2 mm)−0.14 in (−3.5 mm)−0.17%
Revolutions per mile786787+1+0.17%
True speed with the speedometer calibrated for 275/40R17
IndicatedActual on 275/40R17Actual on 215/45R18Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 215/45R18 lowers the vehicle by 0.02 in (0.5 mm) at the axle (half the −1.1 mm diameter difference).

215/45R18 is 0.04 in shorter than 275/40R17 and 60 mm narrower, a 0.17% difference in overall diameter.

With the speedometer calibrated for 275/40R17, an indicated 60 mph is actually 59.9 mph on 215/45R18, and revolutions per mile change from 786 to 787.

215/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 275/40R17.

Size pages

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