235/75R17 vs 245/65R18

245/65R18 is 0.34 in (8.6 mm) shorter than 235/75R17, a −1.10% diameter difference. With the speedometer set for 235/75R17, an indicated 60 mph is 59.3 mph on 245/65R18.

Is this a safe swap?

Diameter difference −1.10%: within the ±3% guideline

By overall diameter alone, 245/65R18 falls inside the ±3% range commonly used as a guideline when replacing 235/75R17. 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.

235/75R17 vs 245/65R18 differences
Measurement	235/75R17	245/65R18	Difference	% diff
Overall diameter	30.88 in (784.3 mm)	30.54 in (775.7 mm)	−0.34 in (−8.6 mm)	−1.10%
Sidewall height	6.94 in (176.3 mm)	6.27 in (159.3 mm)	−0.67 in (−17.0 mm)	−9.65%
Section width	9.25 in (235.0 mm)	9.65 in (245.0 mm)	+0.39 in (+10.0 mm)	+4.26%
Circumference	97.01 in (2,464.0 mm)	95.94 in (2,436.9 mm)	−1.06 in (−27.0 mm)	−1.10%
Revolutions per mile	653	660	+7	+1.11%

True speed with the speedometer calibrated for 235/75R17
Indicated	Actual on 235/75R17	Actual on 245/65R18	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.2 mph	−0.8 mph

Ride-height change: 245/65R18 lowers the vehicle by 0.17 in (4.3 mm) at the axle (half the −8.6 mm diameter difference).

245/65R18 is 0.34 in shorter than 235/75R17 and 10 mm wider, a 1.10% difference in overall diameter.

With the speedometer calibrated for 235/75R17, an indicated 60 mph is actually 59.3 mph on 245/65R18, and revolutions per mile change from 653 to 660.

245/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/75R17.

Size pages

Other comparisons with 235/75R17

Other comparisons with 245/65R18

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