225/45R17 vs 255/40R17

255/40R17 is 0.06 in (1.5 mm) taller than 225/45R17, a +0.24% diameter difference. With the speedometer set for 225/45R17, an indicated 60 mph is 60.1 mph on 255/40R17.

Is this a safe swap?

Diameter difference +0.24%: under 1%

By overall diameter alone, 255/40R17 is a near match for 225/45R17; 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.

225/45R17 vs 255/40R17 differences
Measurement	225/45R17	255/40R17	Difference	% diff
Overall diameter	24.97 in (634.3 mm)	25.03 in (635.8 mm)	+0.06 in (+1.5 mm)	+0.24%
Sidewall height	3.99 in (101.3 mm)	4.02 in (102.0 mm)	+0.03 in (+0.8 mm)	+0.74%
Section width	8.86 in (225.0 mm)	10.04 in (255.0 mm)	+1.18 in (+30.0 mm)	+13.33%
Circumference	78.45 in (1,992.7 mm)	78.64 in (1,997.4 mm)	+0.19 in (+4.7 mm)	+0.24%
Revolutions per mile	808	806	−2	−0.24%

True speed with the speedometer calibrated for 225/45R17
Indicated	Actual on 225/45R17	Actual on 255/40R17	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 255/40R17 raises the vehicle by 0.03 in (0.8 mm) at the axle (half the +1.5 mm diameter difference).

255/40R17 is 0.06 in taller than 225/45R17 and 30 mm wider, a 0.24% difference in overall diameter.

With the speedometer calibrated for 225/45R17, an indicated 60 mph is actually 60.1 mph on 255/40R17, and revolutions per mile change from 808 to 806.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 225/45R17

Other comparisons with 255/40R17

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