245/45R17 vs 215/45R18

215/45R18 is 0.06 in (1.6 mm) shorter than 245/45R17, a −0.25% diameter difference. With the speedometer set for 245/45R17, an indicated 60 mph is 59.9 mph on 215/45R18.

Is this a safe swap?

Diameter difference −0.25%: under 1%

By overall diameter alone, 215/45R18 is a near match for 245/45R17; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

245/45R17 vs 215/45R18 differences
Measurement	245/45R17	215/45R18	Difference	% diff
Overall diameter	25.68 in (652.3 mm)	25.62 in (650.7 mm)	−0.06 in (−1.6 mm)	−0.25%
Sidewall height	4.34 in (110.3 mm)	3.81 in (96.8 mm)	−0.53 in (−13.5 mm)	−12.24%
Section width	9.65 in (245.0 mm)	8.46 in (215.0 mm)	−1.18 in (−30.0 mm)	−12.24%
Circumference	80.68 in (2,049.3 mm)	80.48 in (2,044.2 mm)	−0.20 in (−5.0 mm)	−0.25%
Revolutions per mile	785	787	+2	+0.25%

True speed with the speedometer calibrated for 245/45R17
Indicated	Actual on 245/45R17	Actual on 215/45R18	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 215/45R18 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.6 mm diameter difference).

215/45R18 is 0.06 in shorter than 245/45R17 and 30 mm narrower, a 0.25% difference in overall diameter.

With the speedometer calibrated for 245/45R17, an indicated 60 mph is actually 59.9 mph on 215/45R18, and revolutions per mile change from 785 to 787.

215/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 245/45R17.

Size pages

Other comparisons with 245/45R17

Other comparisons with 215/45R18

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.