235/45R17 vs 255/45R17

255/45R17 is 0.71 in (18.0 mm) taller than 235/45R17, a +2.80% diameter difference. With the speedometer set for 235/45R17, an indicated 60 mph is 61.7 mph on 255/45R17.

Is this a safe swap?

Diameter difference +2.80%: within the ±3% guideline

By overall diameter alone, 255/45R17 falls inside the ±3% range commonly used as a guideline when replacing 235/45R17. 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.

235/45R17 vs 255/45R17 differences
Measurement	235/45R17	255/45R17	Difference	% diff
Overall diameter	25.33 in (643.3 mm)	26.04 in (661.3 mm)	+0.71 in (+18.0 mm)	+2.80%
Sidewall height	4.16 in (105.8 mm)	4.52 in (114.8 mm)	+0.35 in (+9.0 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	79.57 in (2,021.0 mm)	81.79 in (2,077.5 mm)	+2.23 in (+56.5 mm)	+2.80%
Revolutions per mile	796	775	−22	−2.72%

True speed with the speedometer calibrated for 235/45R17
Indicated	Actual on 235/45R17	Actual on 255/45R17	Difference
30 mph	30.0 mph	30.8 mph	+0.8 mph
60 mph	60.0 mph	61.7 mph	+1.7 mph
75 mph	75.0 mph	77.1 mph	+2.1 mph

Ride-height change: 255/45R17 raises the vehicle by 0.35 in (9.0 mm) at the axle (half the +18.0 mm diameter difference).

255/45R17 is 0.71 in taller than 235/45R17 and 20 mm wider, a 2.80% difference in overall diameter.

With the speedometer calibrated for 235/45R17, an indicated 60 mph is actually 61.7 mph on 255/45R17, and revolutions per mile change from 796 to 775.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 235/45R17

Other comparisons with 255/45R17

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