235/35R20 vs 255/35R20

255/35R20 is 0.55 in (14.0 mm) taller than 235/35R20, a +2.08% diameter difference. With the speedometer set for 235/35R20, an indicated 60 mph is 61.2 mph on 255/35R20.

Is this a safe swap?

Diameter difference +2.08%: within the ±3% guideline

By overall diameter alone, 255/35R20 falls inside the ±3% range commonly used as a guideline when replacing 235/35R20. 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.

235/35R20 vs 255/35R20 differences
Measurement	235/35R20	255/35R20	Difference	% diff
Overall diameter	26.48 in (672.5 mm)	27.03 in (686.5 mm)	+0.55 in (+14.0 mm)	+2.08%
Sidewall height	3.24 in (82.3 mm)	3.51 in (89.3 mm)	+0.28 in (+7.0 mm)	+8.51%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	83.18 in (2,112.7 mm)	84.91 in (2,156.7 mm)	+1.73 in (+44.0 mm)	+2.08%
Revolutions per mile	762	746	−16	−2.04%

True speed with the speedometer calibrated for 235/35R20
Indicated	Actual on 235/35R20	Actual on 255/35R20	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.2 mph	+1.2 mph
75 mph	75.0 mph	76.6 mph	+1.6 mph

Ride-height change: 255/35R20 raises the vehicle by 0.28 in (7.0 mm) at the axle (half the +14.0 mm diameter difference).

255/35R20 is 0.55 in taller than 235/35R20 and 20 mm wider, a 2.08% difference in overall diameter.

With the speedometer calibrated for 235/35R20, an indicated 60 mph is actually 61.2 mph on 255/35R20, and revolutions per mile change from 762 to 746.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 235/35R20

Other comparisons with 255/35R20

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