225/70R16 vs 245/55R18

245/55R18 is 0.21 in (5.3 mm) taller than 225/70R16, a +0.73% diameter difference. With the speedometer set for 225/70R16, an indicated 60 mph is 60.4 mph on 245/55R18.

Is this a safe swap?

Diameter difference +0.73%: under 1%

By overall diameter alone, 245/55R18 is a near match for 225/70R16; 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.

225/70R16 vs 245/55R18 differences
Measurement	225/70R16	245/55R18	Difference	% diff
Overall diameter	28.40 in (721.4 mm)	28.61 in (726.7 mm)	+0.21 in (+5.3 mm)	+0.73%
Sidewall height	6.20 in (157.5 mm)	5.31 in (134.8 mm)	−0.90 in (−22.7 mm)	−14.44%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	89.23 in (2,266.3 mm)	89.88 in (2,283.0 mm)	+0.66 in (+16.7 mm)	+0.73%
Revolutions per mile	710	705	−5	−0.73%

True speed with the speedometer calibrated for 225/70R16
Indicated	Actual on 225/70R16	Actual on 245/55R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 245/55R18 raises the vehicle by 0.10 in (2.7 mm) at the axle (half the +5.3 mm diameter difference).

245/55R18 is 0.21 in taller than 225/70R16 and 20 mm wider, a 0.73% difference in overall diameter.

With the speedometer calibrated for 225/70R16, an indicated 60 mph is actually 60.4 mph on 245/55R18, and revolutions per mile change from 710 to 705.

245/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/70R16.

Size pages

Other comparisons with 225/70R16

Other comparisons with 245/55R18

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