245/35R19 vs 255/30R20

255/30R20 is 0.27 in (6.9 mm) taller than 245/35R19, a +1.05% diameter difference. With the speedometer set for 245/35R19, an indicated 60 mph is 60.6 mph on 255/30R20.

Is this a safe swap?

Diameter difference +1.05%: within the ±3% guideline

By overall diameter alone, 255/30R20 falls inside the ±3% range commonly used as a guideline when replacing 245/35R19. 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.

245/35R19 vs 255/30R20 differences
Measurement	245/35R19	255/30R20	Difference	% diff
Overall diameter	25.75 in (654.1 mm)	26.02 in (661.0 mm)	+0.27 in (+6.9 mm)	+1.05%
Sidewall height	3.38 in (85.8 mm)	3.01 in (76.5 mm)	−0.36 in (−9.2 mm)	−10.79%
Section width	9.65 in (245.0 mm)	10.04 in (255.0 mm)	+0.39 in (+10.0 mm)	+4.08%
Circumference	80.90 in (2,054.9 mm)	81.76 in (2,076.6 mm)	+0.85 in (+21.7 mm)	+1.05%
Revolutions per mile	783	775	−8	−1.04%

True speed with the speedometer calibrated for 245/35R19
Indicated	Actual on 245/35R19	Actual on 255/30R20	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: 255/30R20 raises the vehicle by 0.14 in (3.5 mm) at the axle (half the +6.9 mm diameter difference).

255/30R20 is 0.27 in taller than 245/35R19 and 10 mm wider, a 1.05% difference in overall diameter.

With the speedometer calibrated for 245/35R19, an indicated 60 mph is actually 60.6 mph on 255/30R20, and revolutions per mile change from 783 to 775.

255/30R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 245/35R19.

Size pages

Other comparisons with 245/35R19

Other comparisons with 255/30R20

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