215/70R16 vs 255/50R18

255/50R18 is 0.19 in (4.8 mm) taller than 215/70R16, a +0.68% diameter difference. With the speedometer set for 215/70R16, an indicated 60 mph is 60.4 mph on 255/50R18.

Is this a safe swap?

Diameter difference +0.68%: under 1%

By overall diameter alone, 255/50R18 is a near match for 215/70R16; 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.

215/70R16 vs 255/50R18 differences
Measurement	215/70R16	255/50R18	Difference	% diff
Overall diameter	27.85 in (707.4 mm)	28.04 in (712.2 mm)	+0.19 in (+4.8 mm)	+0.68%
Sidewall height	5.93 in (150.5 mm)	5.02 in (127.5 mm)	−0.91 in (−23.0 mm)	−15.28%
Section width	8.46 in (215.0 mm)	10.04 in (255.0 mm)	+1.57 in (+40.0 mm)	+18.60%
Circumference	87.49 in (2,222.4 mm)	88.09 in (2,237.4 mm)	+0.59 in (+15.1 mm)	+0.68%
Revolutions per mile	724	719	−5	−0.67%

True speed with the speedometer calibrated for 215/70R16
Indicated	Actual on 215/70R16	Actual on 255/50R18	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	75.5 mph	+0.5 mph

Ride-height change: 255/50R18 raises the vehicle by 0.09 in (2.4 mm) at the axle (half the +4.8 mm diameter difference).

255/50R18 is 0.19 in taller than 215/70R16 and 40 mm wider, a 0.68% difference in overall diameter.

With the speedometer calibrated for 215/70R16, an indicated 60 mph is actually 60.4 mph on 255/50R18, and revolutions per mile change from 724 to 719.

255/50R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 215/70R16.

Size pages

Other comparisons with 215/70R16

Other comparisons with 255/50R18

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