255/65R16 vs 245/55R18

245/55R18 is 0.44 in (11.2 mm) shorter than 255/65R16, a −1.52% diameter difference. With the speedometer set for 255/65R16, an indicated 60 mph is 59.1 mph on 245/55R18.

Is this a safe swap?

Diameter difference −1.52%: within the ±3% guideline

By overall diameter alone, 245/55R18 falls inside the ±3% range commonly used as a guideline when replacing 255/65R16. 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.

255/65R16 vs 245/55R18 differences
Measurement	255/65R16	245/55R18	Difference	% diff
Overall diameter	29.05 in (737.9 mm)	28.61 in (726.7 mm)	−0.44 in (−11.2 mm)	−1.52%
Sidewall height	6.53 in (165.8 mm)	5.31 in (134.8 mm)	−1.22 in (−31.0 mm)	−18.70%
Section width	10.04 in (255.0 mm)	9.65 in (245.0 mm)	−0.39 in (−10.0 mm)	−3.92%
Circumference	91.27 in (2,318.2 mm)	89.88 in (2,283.0 mm)	−1.39 in (−35.2 mm)	−1.52%
Revolutions per mile	694	705	+11	+1.54%

True speed with the speedometer calibrated for 255/65R16
Indicated	Actual on 255/65R16	Actual on 245/55R18	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.9 mph	−1.1 mph

Ride-height change: 245/55R18 lowers the vehicle by 0.22 in (5.6 mm) at the axle (half the −11.2 mm diameter difference).

245/55R18 is 0.44 in shorter than 255/65R16 and 10 mm narrower, a 1.52% difference in overall diameter.

With the speedometer calibrated for 255/65R16, an indicated 60 mph is actually 59.1 mph on 245/55R18, and revolutions per mile change from 694 to 705.

245/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 255/65R16.

Size pages

Other comparisons with 255/65R16

Other comparisons with 245/55R18

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