235/70R16 vs 245/55R18

245/55R18 is 0.34 in (8.7 mm) shorter than 235/70R16, a −1.18% diameter difference. With the speedometer set for 235/70R16, an indicated 60 mph is 59.3 mph on 245/55R18.

Is this a safe swap?

Diameter difference −1.18%: within the ±3% guideline

By overall diameter alone, 245/55R18 falls inside the ±3% range commonly used as a guideline when replacing 235/70R16. 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.

235/70R16 vs 245/55R18 differences
Measurement	235/70R16	245/55R18	Difference	% diff
Overall diameter	28.95 in (735.4 mm)	28.61 in (726.7 mm)	−0.34 in (−8.7 mm)	−1.18%
Sidewall height	6.48 in (164.5 mm)	5.31 in (134.8 mm)	−1.17 in (−29.7 mm)	−18.09%
Section width	9.25 in (235.0 mm)	9.65 in (245.0 mm)	+0.39 in (+10.0 mm)	+4.26%
Circumference	90.96 in (2,310.3 mm)	89.88 in (2,283.0 mm)	−1.08 in (−27.3 mm)	−1.18%
Revolutions per mile	697	705	+8	+1.20%

True speed with the speedometer calibrated for 235/70R16
Indicated	Actual on 235/70R16	Actual on 245/55R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.1 mph	−0.9 mph

Ride-height change: 245/55R18 lowers the vehicle by 0.17 in (4.3 mm) at the axle (half the −8.7 mm diameter difference).

245/55R18 is 0.34 in shorter than 235/70R16 and 10 mm wider, a 1.18% difference in overall diameter.

With the speedometer calibrated for 235/70R16, an indicated 60 mph is actually 59.3 mph on 245/55R18, and revolutions per mile change from 697 to 705.

245/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/70R16.

Size pages

Other comparisons with 235/70R16

Other comparisons with 245/55R18

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