235/75R17 vs 255/75R17

255/75R17 is 1.18 in (30.0 mm) taller than 235/75R17, a +3.83% diameter difference. With the speedometer set for 235/75R17, an indicated 60 mph is 62.3 mph on 255/75R17.

Is this a safe swap?

Diameter difference +3.83%: outside the ±3% guideline

By overall diameter alone, 255/75R17 falls outside the ±3% range commonly used as a guideline when replacing 235/75R17; speedometer and ride-height changes are larger. 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.

235/75R17 vs 255/75R17 differences
Measurement	235/75R17	255/75R17	Difference	% diff
Overall diameter	30.88 in (784.3 mm)	32.06 in (814.3 mm)	+1.18 in (+30.0 mm)	+3.83%
Sidewall height	6.94 in (176.3 mm)	7.53 in (191.3 mm)	+0.59 in (+15.0 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	97.01 in (2,464.0 mm)	100.72 in (2,558.2 mm)	+3.71 in (+94.2 mm)	+3.83%
Revolutions per mile	653	629	−24	−3.68%

True speed with the speedometer calibrated for 235/75R17
Indicated	Actual on 235/75R17	Actual on 255/75R17	Difference
30 mph	30.0 mph	31.1 mph	+1.1 mph
60 mph	60.0 mph	62.3 mph	+2.3 mph
75 mph	75.0 mph	77.9 mph	+2.9 mph

Ride-height change: 255/75R17 raises the vehicle by 0.59 in (15.0 mm) at the axle (half the +30.0 mm diameter difference).

255/75R17 is 1.18 in taller than 235/75R17 and 20 mm wider, a 3.83% difference in overall diameter.

With the speedometer calibrated for 235/75R17, an indicated 60 mph is actually 62.3 mph on 255/75R17, and revolutions per mile change from 653 to 629.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 235/75R17

Other comparisons with 255/75R17

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