235/65R19 vs 255/55R20

255/55R20 is 0.02 in (0.4 mm) taller than 235/65R19, a +0.05% diameter difference. With the speedometer set for 235/65R19, an indicated 60 mph is 60.0 mph on 255/55R20.

Is this a safe swap?

Diameter difference +0.05%: under 1%

By overall diameter alone, 255/55R20 is a near match for 235/65R19; 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.

235/65R19 vs 255/55R20 differences
Measurement	235/65R19	255/55R20	Difference	% diff
Overall diameter	31.03 in (788.1 mm)	31.04 in (788.5 mm)	+0.02 in (+0.4 mm)	+0.05%
Sidewall height	6.01 in (152.8 mm)	5.52 in (140.3 mm)	−0.49 in (−12.5 mm)	−8.18%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	97.48 in (2,475.9 mm)	97.53 in (2,477.1 mm)	+0.05 in (+1.3 mm)	+0.05%
Revolutions per mile	650	650	0	−0.05%

True speed with the speedometer calibrated for 235/65R19
Indicated	Actual on 235/65R19	Actual on 255/55R20
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: 255/55R20 raises the vehicle by 0.01 in (0.2 mm) at the axle (half the +0.4 mm diameter difference).

255/55R20 is 0.02 in taller than 235/65R19 and 20 mm wider, a 0.05% difference in overall diameter.

With the speedometer calibrated for 235/65R19, an indicated 60 mph is actually 60.0 mph on 255/55R20, and revolutions per mile change from 650 to 650.

255/55R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 235/65R19.

Size pages

Other comparisons with 235/65R19

Other comparisons with 255/55R20

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