245/40R19 vs 285/30R20

285/30R20 is 0.02 in (0.4 mm) taller than 245/40R19, a +0.06% diameter difference. With the speedometer set for 245/40R19, an indicated 60 mph is 60.0 mph on 285/30R20.

Is this a safe swap?

Diameter difference +0.06%: under 1%

By overall diameter alone, 285/30R20 is a near match for 245/40R19; 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.

245/40R19 vs 285/30R20 differences
Measurement	245/40R19	285/30R20	Difference	% diff
Overall diameter	26.72 in (678.6 mm)	26.73 in (679.0 mm)	+0.02 in (+0.4 mm)	+0.06%
Sidewall height	3.86 in (98.0 mm)	3.37 in (85.5 mm)	−0.49 in (−12.5 mm)	−12.76%
Section width	9.65 in (245.0 mm)	11.22 in (285.0 mm)	+1.57 in (+40.0 mm)	+16.33%
Circumference	83.93 in (2,131.9 mm)	83.98 in (2,133.1 mm)	+0.05 in (+1.3 mm)	+0.06%
Revolutions per mile	755	754	0	−0.06%

True speed with the speedometer calibrated for 245/40R19
Indicated	Actual on 245/40R19	Actual on 285/30R20
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 285/30R20 raises the vehicle by 0.01 in (0.2 mm) at the axle (half the +0.4 mm diameter difference).

285/30R20 is 0.02 in taller than 245/40R19 and 40 mm wider, a 0.06% difference in overall diameter.

With the speedometer calibrated for 245/40R19, an indicated 60 mph is actually 60.0 mph on 285/30R20, and revolutions per mile change from 755 to 754.

285/30R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 245/40R19.

Size pages

Other comparisons with 245/40R19

Other comparisons with 285/30R20

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