285/30R19 vs 255/30R20

255/30R20 is 0.29 in (7.4 mm) taller than 285/30R19, a +1.13% diameter difference. With the speedometer set for 285/30R19, an indicated 60 mph is 60.7 mph on 255/30R20.

Is this a safe swap?

Diameter difference +1.13%: within the ±3% guideline

By overall diameter alone, 255/30R20 falls inside the ±3% range commonly used as a guideline when replacing 285/30R19. 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.

285/30R19 vs 255/30R20 differences
Measurement	285/30R19	255/30R20	Difference	% diff
Overall diameter	25.73 in (653.6 mm)	26.02 in (661.0 mm)	+0.29 in (+7.4 mm)	+1.13%
Sidewall height	3.37 in (85.5 mm)	3.01 in (76.5 mm)	−0.35 in (−9.0 mm)	−10.53%
Section width	11.22 in (285.0 mm)	10.04 in (255.0 mm)	−1.18 in (−30.0 mm)	−10.53%
Circumference	80.84 in (2,053.3 mm)	81.76 in (2,076.6 mm)	+0.92 in (+23.2 mm)	+1.13%
Revolutions per mile	784	775	−9	−1.12%

True speed with the speedometer calibrated for 285/30R19
Indicated	Actual on 285/30R19	Actual on 255/30R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 255/30R20 raises the vehicle by 0.15 in (3.7 mm) at the axle (half the +7.4 mm diameter difference).

255/30R20 is 0.29 in taller than 285/30R19 and 30 mm narrower, a 1.13% difference in overall diameter.

With the speedometer calibrated for 285/30R19, an indicated 60 mph is actually 60.7 mph on 255/30R20, and revolutions per mile change from 784 to 775.

255/30R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 285/30R19.

Size pages

Other comparisons with 285/30R19

Other comparisons with 255/30R20

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