225/75R17 vs 235/65R18

235/65R18 is 0.26 in (6.6 mm) shorter than 225/75R17, a −0.86% diameter difference. With the speedometer set for 225/75R17, an indicated 60 mph is 59.5 mph on 235/65R18.

Is this a safe swap?

Diameter difference −0.86%: under 1%

By overall diameter alone, 235/65R18 is a near match for 225/75R17; 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.

225/75R17 vs 235/65R18 differences
Measurement	225/75R17	235/65R18	Difference	% diff
Overall diameter	30.29 in (769.3 mm)	30.03 in (762.7 mm)	−0.26 in (−6.6 mm)	−0.86%
Sidewall height	6.64 in (168.8 mm)	6.01 in (152.8 mm)	−0.63 in (−16.0 mm)	−9.48%
Section width	8.86 in (225.0 mm)	9.25 in (235.0 mm)	+0.39 in (+10.0 mm)	+4.44%
Circumference	95.15 in (2,416.8 mm)	94.33 in (2,396.1 mm)	−0.82 in (−20.7 mm)	−0.86%
Revolutions per mile	666	672	+6	+0.87%

True speed with the speedometer calibrated for 225/75R17
Indicated	Actual on 225/75R17	Actual on 235/65R18	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	74.4 mph	−0.6 mph

Ride-height change: 235/65R18 lowers the vehicle by 0.13 in (3.3 mm) at the axle (half the −6.6 mm diameter difference).

235/65R18 is 0.26 in shorter than 225/75R17 and 10 mm wider, a 0.86% difference in overall diameter.

With the speedometer calibrated for 225/75R17, an indicated 60 mph is actually 59.5 mph on 235/65R18, and revolutions per mile change from 666 to 672.

235/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/75R17.

Size pages

Other comparisons with 225/75R17

Other comparisons with 235/65R18

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