215/45R17 vs 245/35R18

245/35R18 is 0.13 in (3.4 mm) taller than 215/45R17, a +0.54% diameter difference. With the speedometer set for 215/45R17, an indicated 60 mph is 60.3 mph on 245/35R18.

Is this a safe swap?

Diameter difference +0.54%: under 1%

By overall diameter alone, 245/35R18 is a near match for 215/45R17; 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.

215/45R17 vs 245/35R18 differences
Measurement	215/45R17	245/35R18	Difference	% diff
Overall diameter	24.62 in (625.3 mm)	24.75 in (628.7 mm)	+0.13 in (+3.4 mm)	+0.54%
Sidewall height	3.81 in (96.8 mm)	3.38 in (85.8 mm)	−0.43 in (−11.0 mm)	−11.37%
Section width	8.46 in (215.0 mm)	9.65 in (245.0 mm)	+1.18 in (+30.0 mm)	+13.95%
Circumference	77.34 in (1,964.4 mm)	77.76 in (1,975.1 mm)	+0.42 in (+10.7 mm)	+0.54%
Revolutions per mile	819	815	−4	−0.54%

True speed with the speedometer calibrated for 215/45R17
Indicated	Actual on 215/45R17	Actual on 245/35R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 245/35R18 raises the vehicle by 0.07 in (1.7 mm) at the axle (half the +3.4 mm diameter difference).

245/35R18 is 0.13 in taller than 215/45R17 and 30 mm wider, a 0.54% difference in overall diameter.

With the speedometer calibrated for 215/45R17, an indicated 60 mph is actually 60.3 mph on 245/35R18, and revolutions per mile change from 819 to 815.

245/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 215/45R17.

Size pages

Other comparisons with 215/45R17

Other comparisons with 245/35R18

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