205/55R17 vs 255/45R17

255/45R17 is 0.16 in (4.0 mm) taller than 205/55R17, a +0.61% diameter difference. With the speedometer set for 205/55R17, an indicated 60 mph is 60.4 mph on 255/45R17.

Is this a safe swap?

Diameter difference +0.61%: under 1%

By overall diameter alone, 255/45R17 is a near match for 205/55R17; the speedometer changes by less than 1%. 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.

205/55R17 vs 255/45R17 differences
Measurement	205/55R17	255/45R17	Difference	% diff
Overall diameter	25.88 in (657.3 mm)	26.04 in (661.3 mm)	+0.16 in (+4.0 mm)	+0.61%
Sidewall height	4.44 in (112.8 mm)	4.52 in (114.8 mm)	+0.08 in (+2.0 mm)	+1.77%
Section width	8.07 in (205.0 mm)	10.04 in (255.0 mm)	+1.97 in (+50.0 mm)	+24.39%
Circumference	81.30 in (2,065.0 mm)	81.79 in (2,077.5 mm)	+0.49 in (+12.6 mm)	+0.61%
Revolutions per mile	779	775	−5	−0.60%

True speed with the speedometer calibrated for 205/55R17
Indicated	Actual on 205/55R17	Actual on 255/45R17	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 255/45R17 raises the vehicle by 0.08 in (2.0 mm) at the axle (half the +4.0 mm diameter difference).

255/45R17 is 0.16 in taller than 205/55R17 and 50 mm wider, a 0.61% difference in overall diameter.

With the speedometer calibrated for 205/55R17, an indicated 60 mph is actually 60.4 mph on 255/45R17, and revolutions per mile change from 779 to 775.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 205/55R17

Other comparisons with 255/45R17

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