225/70R16 vs 255/50R18

255/50R18 is 0.36 in (9.2 mm) shorter than 225/70R16, a −1.28% diameter difference. With the speedometer set for 225/70R16, an indicated 60 mph is 59.2 mph on 255/50R18.

Is this a safe swap?

Diameter difference −1.28%: within the ±3% guideline

By overall diameter alone, 255/50R18 falls inside the ±3% range commonly used as a guideline when replacing 225/70R16. 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.

225/70R16 vs 255/50R18 differences
Measurement	225/70R16	255/50R18	Difference	% diff
Overall diameter	28.40 in (721.4 mm)	28.04 in (712.2 mm)	−0.36 in (−9.2 mm)	−1.28%
Sidewall height	6.20 in (157.5 mm)	5.02 in (127.5 mm)	−1.18 in (−30.0 mm)	−19.05%
Section width	8.86 in (225.0 mm)	10.04 in (255.0 mm)	+1.18 in (+30.0 mm)	+13.33%
Circumference	89.23 in (2,266.3 mm)	88.09 in (2,237.4 mm)	−1.14 in (−28.9 mm)	−1.28%
Revolutions per mile	710	719	+9	+1.29%

True speed with the speedometer calibrated for 225/70R16
Indicated	Actual on 225/70R16	Actual on 255/50R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.2 mph	−0.8 mph
75 mph	75.0 mph	74.0 mph	−1.0 mph

Ride-height change: 255/50R18 lowers the vehicle by 0.18 in (4.6 mm) at the axle (half the −9.2 mm diameter difference).

255/50R18 is 0.36 in shorter than 225/70R16 and 30 mm wider, a 1.28% difference in overall diameter.

With the speedometer calibrated for 225/70R16, an indicated 60 mph is actually 59.2 mph on 255/50R18, and revolutions per mile change from 710 to 719.

255/50R18 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 255/50R18

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