225/45R17 vs 245/35R18

245/35R18 is 0.22 in (5.6 mm) shorter than 225/45R17, a −0.88% diameter difference. With the speedometer set for 225/45R17, an indicated 60 mph is 59.5 mph on 245/35R18.

Is this a safe swap?

Diameter difference −0.88%: under 1%

By overall diameter alone, 245/35R18 is a near match for 225/45R17; 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.

225/45R17 vs 245/35R18 differences
Measurement	225/45R17	245/35R18	Difference	% diff
Overall diameter	24.97 in (634.3 mm)	24.75 in (628.7 mm)	−0.22 in (−5.6 mm)	−0.88%
Sidewall height	3.99 in (101.3 mm)	3.38 in (85.8 mm)	−0.61 in (−15.5 mm)	−15.31%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	78.45 in (1,992.7 mm)	77.76 in (1,975.1 mm)	−0.69 in (−17.6 mm)	−0.88%
Revolutions per mile	808	815	+7	+0.89%

True speed with the speedometer calibrated for 225/45R17
Indicated	Actual on 225/45R17	Actual on 245/35R18	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.5 mph	−0.5 mph
75 mph	75.0 mph	74.3 mph	−0.7 mph

Ride-height change: 245/35R18 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.6 mm diameter difference).

245/35R18 is 0.22 in shorter than 225/45R17 and 20 mm wider, a 0.88% difference in overall diameter.

With the speedometer calibrated for 225/45R17, an indicated 60 mph is actually 59.5 mph on 245/35R18, and revolutions per mile change from 808 to 815.

245/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/45R17.

Size pages

Other comparisons with 225/45R17

Other comparisons with 245/35R18

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