215/40R18 vs 255/30R19

255/30R19 is 0.25 in (6.4 mm) taller than 215/40R18, a +1.02% diameter difference. With the speedometer set for 215/40R18, an indicated 60 mph is 60.6 mph on 255/30R19.

Is this a safe swap?

Diameter difference +1.02%: within the ±3% guideline

By overall diameter alone, 255/30R19 falls inside the ±3% range commonly used as a guideline when replacing 215/40R18. 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.

215/40R18 vs 255/30R19 differences
Measurement	215/40R18	255/30R19	Difference	% diff
Overall diameter	24.77 in (629.2 mm)	25.02 in (635.6 mm)	+0.25 in (+6.4 mm)	+1.02%
Sidewall height	3.39 in (86.0 mm)	3.01 in (76.5 mm)	−0.37 in (−9.5 mm)	−11.05%
Section width	8.46 in (215.0 mm)	10.04 in (255.0 mm)	+1.57 in (+40.0 mm)	+18.60%
Circumference	77.82 in (1,976.7 mm)	78.61 in (1,996.8 mm)	+0.79 in (+20.1 mm)	+1.02%
Revolutions per mile	814	806	−8	−1.01%

True speed with the speedometer calibrated for 215/40R18
Indicated	Actual on 215/40R18	Actual on 255/30R19	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 255/30R19 raises the vehicle by 0.13 in (3.2 mm) at the axle (half the +6.4 mm diameter difference).

255/30R19 is 0.25 in taller than 215/40R18 and 40 mm wider, a 1.02% difference in overall diameter.

With the speedometer calibrated for 215/40R18, an indicated 60 mph is actually 60.6 mph on 255/30R19, and revolutions per mile change from 814 to 806.

255/30R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 215/40R18.

Size pages

Other comparisons with 215/40R18

Other comparisons with 255/30R19

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