255/40R17 vs 205/50R17

205/50R17 is 0.04 in (1.0 mm) taller than 255/40R17, a +0.16% diameter difference. With the speedometer set for 255/40R17, an indicated 60 mph is 60.1 mph on 205/50R17.

Is this a safe swap?

Diameter difference +0.16%: under 1%

By overall diameter alone, 205/50R17 is a near match for 255/40R17; 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.

255/40R17 vs 205/50R17 differences
Measurement	255/40R17	205/50R17	Difference	% diff
Overall diameter	25.03 in (635.8 mm)	25.07 in (636.8 mm)	+0.04 in (+1.0 mm)	+0.16%
Sidewall height	4.02 in (102.0 mm)	4.04 in (102.5 mm)	+0.02 in (+0.5 mm)	+0.49%
Section width	10.04 in (255.0 mm)	8.07 in (205.0 mm)	−1.97 in (−50.0 mm)	−19.61%
Circumference	78.64 in (1,997.4 mm)	78.76 in (2,000.6 mm)	+0.12 in (+3.1 mm)	+0.16%
Revolutions per mile	806	804	−1	−0.16%

True speed with the speedometer calibrated for 255/40R17
Indicated	Actual on 255/40R17	Actual on 205/50R17	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 205/50R17 raises the vehicle by 0.02 in (0.5 mm) at the axle (half the +1.0 mm diameter difference).

205/50R17 is 0.04 in taller than 255/40R17 and 50 mm narrower, a 0.16% difference in overall diameter.

With the speedometer calibrated for 255/40R17, an indicated 60 mph is actually 60.1 mph on 205/50R17, and revolutions per mile change from 806 to 804.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 255/40R17

Other comparisons with 205/50R17

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