215/50R18 vs 285/30R20

285/30R20 is 0.27 in (6.8 mm) taller than 215/50R18, a +1.01% diameter difference. With the speedometer set for 215/50R18, an indicated 60 mph is 60.6 mph on 285/30R20.

Is this a safe swap?

Diameter difference +1.01%: within the ±3% guideline

By overall diameter alone, 285/30R20 falls inside the ±3% range commonly used as a guideline when replacing 215/50R18. 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.

215/50R18 vs 285/30R20 differences
Measurement	215/50R18	285/30R20	Difference	% diff
Overall diameter	26.46 in (672.2 mm)	26.73 in (679.0 mm)	+0.27 in (+6.8 mm)	+1.01%
Sidewall height	4.23 in (107.5 mm)	3.37 in (85.5 mm)	−0.87 in (−22.0 mm)	−20.47%
Section width	8.46 in (215.0 mm)	11.22 in (285.0 mm)	+2.76 in (+70.0 mm)	+32.56%
Circumference	83.14 in (2,111.8 mm)	83.98 in (2,133.1 mm)	+0.84 in (+21.4 mm)	+1.01%
Revolutions per mile	762	754	−8	−1.00%

True speed with the speedometer calibrated for 215/50R18
Indicated	Actual on 215/50R18	Actual on 285/30R20	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: 285/30R20 raises the vehicle by 0.13 in (3.4 mm) at the axle (half the +6.8 mm diameter difference).

285/30R20 is 0.27 in taller than 215/50R18 and 70 mm wider, a 1.01% difference in overall diameter.

With the speedometer calibrated for 215/50R18, an indicated 60 mph is actually 60.6 mph on 285/30R20, and revolutions per mile change from 762 to 754.

285/30R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 215/50R18.

Size pages

Other comparisons with 215/50R18

Other comparisons with 285/30R20

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