205/45R17 vs 235/35R18

235/35R18 is 0.21 in (5.4 mm) taller than 205/45R17, a +0.88% diameter difference. With the speedometer set for 205/45R17, an indicated 60 mph is 60.5 mph on 235/35R18.

Is this a safe swap?

Diameter difference +0.88%: under 1%

By overall diameter alone, 235/35R18 is a near match for 205/45R17; 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.

205/45R17 vs 235/35R18 differences
Measurement	205/45R17	235/35R18	Difference	% diff
Overall diameter	24.26 in (616.3 mm)	24.48 in (621.7 mm)	+0.21 in (+5.4 mm)	+0.88%
Sidewall height	3.63 in (92.3 mm)	3.24 in (82.3 mm)	−0.39 in (−10.0 mm)	−10.84%
Section width	8.07 in (205.0 mm)	9.25 in (235.0 mm)	+1.18 in (+30.0 mm)	+14.63%
Circumference	76.23 in (1,936.2 mm)	76.89 in (1,953.1 mm)	+0.67 in (+17.0 mm)	+0.88%
Revolutions per mile	831	824	−7	−0.87%

True speed with the speedometer calibrated for 205/45R17
Indicated	Actual on 205/45R17	Actual on 235/35R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 235/35R18 raises the vehicle by 0.11 in (2.7 mm) at the axle (half the +5.4 mm diameter difference).

235/35R18 is 0.21 in taller than 205/45R17 and 30 mm wider, a 0.88% difference in overall diameter.

With the speedometer calibrated for 205/45R17, an indicated 60 mph is actually 60.5 mph on 235/35R18, and revolutions per mile change from 831 to 824.

235/35R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 205/45R17.

Size pages

Other comparisons with 205/45R17

Other comparisons with 235/35R18

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