215/75R16 vs 255/55R18

255/55R18 is 0.35 in (8.8 mm) taller than 215/75R16, a +1.21% diameter difference. With the speedometer set for 215/75R16, an indicated 60 mph is 60.7 mph on 255/55R18.

Is this a safe swap?

Diameter difference +1.21%: within the ±3% guideline

By overall diameter alone, 255/55R18 falls inside the ±3% range commonly used as a guideline when replacing 215/75R16. 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.

215/75R16 vs 255/55R18 differences
Measurement	215/75R16	255/55R18	Difference	% diff
Overall diameter	28.70 in (728.9 mm)	29.04 in (737.7 mm)	+0.35 in (+8.8 mm)	+1.21%
Sidewall height	6.35 in (161.3 mm)	5.52 in (140.3 mm)	−0.83 in (−21.0 mm)	−13.02%
Section width	8.46 in (215.0 mm)	10.04 in (255.0 mm)	+1.57 in (+40.0 mm)	+18.60%
Circumference	90.15 in (2,289.9 mm)	91.24 in (2,317.6 mm)	+1.09 in (+27.6 mm)	+1.21%
Revolutions per mile	703	694	−8	−1.19%

True speed with the speedometer calibrated for 215/75R16
Indicated	Actual on 215/75R16	Actual on 255/55R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 255/55R18 raises the vehicle by 0.17 in (4.4 mm) at the axle (half the +8.8 mm diameter difference).

255/55R18 is 0.35 in taller than 215/75R16 and 40 mm wider, a 1.21% difference in overall diameter.

With the speedometer calibrated for 215/75R16, an indicated 60 mph is actually 60.7 mph on 255/55R18, and revolutions per mile change from 703 to 694.

255/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 215/75R16.

Size pages

Other comparisons with 215/75R16

Other comparisons with 255/55R18

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