245/45R17 vs 255/45R17

255/45R17 is 0.35 in (9.0 mm) taller than 245/45R17, a +1.38% diameter difference. With the speedometer set for 245/45R17, an indicated 60 mph is 60.8 mph on 255/45R17.

Is this a safe swap?

Diameter difference +1.38%: within the ±3% guideline

By overall diameter alone, 255/45R17 falls inside the ±3% range commonly used as a guideline when replacing 245/45R17. 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.

245/45R17 vs 255/45R17 differences
Measurement	245/45R17	255/45R17	Difference	% diff
Overall diameter	25.68 in (652.3 mm)	26.04 in (661.3 mm)	+0.35 in (+9.0 mm)	+1.38%
Sidewall height	4.34 in (110.3 mm)	4.52 in (114.8 mm)	+0.18 in (+4.5 mm)	+4.08%
Section width	9.65 in (245.0 mm)	10.04 in (255.0 mm)	+0.39 in (+10.0 mm)	+4.08%
Circumference	80.68 in (2,049.3 mm)	81.79 in (2,077.5 mm)	+1.11 in (+28.3 mm)	+1.38%
Revolutions per mile	785	775	−11	−1.36%

True speed with the speedometer calibrated for 245/45R17
Indicated	Actual on 245/45R17	Actual on 255/45R17	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 255/45R17 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

255/45R17 is 0.35 in taller than 245/45R17 and 10 mm wider, a 1.38% difference in overall diameter.

With the speedometer calibrated for 245/45R17, an indicated 60 mph is actually 60.8 mph on 255/45R17, and revolutions per mile change from 785 to 775.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 245/45R17

Other comparisons with 255/45R17

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