205/75R15 vs 255/50R17

255/50R17 is 0.07 in (1.7 mm) shorter than 205/75R15, a −0.25% diameter difference. With the speedometer set for 205/75R15, an indicated 60 mph is 59.9 mph on 255/50R17.

Is this a safe swap?

Diameter difference −0.25%: under 1%

By overall diameter alone, 255/50R17 is a near match for 205/75R15; 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.

205/75R15 vs 255/50R17 differences
Measurement	205/75R15	255/50R17	Difference	% diff
Overall diameter	27.11 in (688.5 mm)	27.04 in (686.8 mm)	−0.07 in (−1.7 mm)	−0.25%
Sidewall height	6.05 in (153.8 mm)	5.02 in (127.5 mm)	−1.03 in (−26.2 mm)	−17.07%
Section width	8.07 in (205.0 mm)	10.04 in (255.0 mm)	+1.97 in (+50.0 mm)	+24.39%
Circumference	85.16 in (2,163.0 mm)	84.95 in (2,157.6 mm)	−0.21 in (−5.3 mm)	−0.25%
Revolutions per mile	744	746	+2	+0.25%

True speed with the speedometer calibrated for 205/75R15
Indicated	Actual on 205/75R15	Actual on 255/50R17	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 255/50R17 lowers the vehicle by 0.03 in (0.9 mm) at the axle (half the −1.7 mm diameter difference).

255/50R17 is 0.07 in shorter than 205/75R15 and 50 mm wider, a 0.25% difference in overall diameter.

With the speedometer calibrated for 205/75R15, an indicated 60 mph is actually 59.9 mph on 255/50R17, and revolutions per mile change from 744 to 746.

255/50R17 mounts on a 17-inch wheel, a plus-2 fitment from the 15-inch wheel of 205/75R15.

Size pages

Other comparisons with 205/75R15

Other comparisons with 255/50R17

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