TireSizesFinder

255/65R17 vs 235/65R18

235/65R18 is 0.02 in (0.6 mm) shorter than 255/65R17, a −0.08% diameter difference. With the speedometer set for 255/65R17, an indicated 60 mph is 60.0 mph on 235/65R18.

Is this a safe swap?

Diameter difference −0.08%: under 1%

By overall diameter alone, 235/65R18 is a near match for 255/65R17; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/65R17 (30.05 in) vs 235/65R18 (30.03 in)255/65R1730.05 in × 10.04 in235/65R1830.03 in × 9.25 in
Side profile and tread width, drawn to the same scale.
255/65R17 vs 235/65R18 differences
Measurement255/65R17235/65R18Difference% diff
Overall diameter30.05 in (763.3 mm)30.03 in (762.7 mm)−0.02 in (−0.6 mm)−0.08%
Sidewall height6.53 in (165.8 mm)6.01 in (152.8 mm)−0.51 in (−13.0 mm)−7.84%
Section width10.04 in (255.0 mm)9.25 in (235.0 mm)−0.79 in (−20.0 mm)−7.84%
Circumference94.41 in (2,398.0 mm)94.33 in (2,396.1 mm)−0.07 in (−1.9 mm)−0.08%
Revolutions per mile671672+1+0.08%
True speed with the speedometer calibrated for 255/65R17
IndicatedActual on 255/65R17Actual on 235/65R18Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 235/65R18 lowers the vehicle by 0.01 in (0.3 mm) at the axle (half the −0.6 mm diameter difference).

235/65R18 is 0.02 in shorter than 255/65R17 and 20 mm narrower, a 0.08% difference in overall diameter.

With the speedometer calibrated for 255/65R17, an indicated 60 mph is actually 60.0 mph on 235/65R18, and revolutions per mile change from 671 to 672.

235/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/65R17.

Size pages

Other comparisons with 255/65R17

Other comparisons with 235/65R18

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.