255/50R17 vs 255/40R19

255/40R19 is 0.01 in (0.2 mm) shorter than 255/50R17, a −0.03% diameter difference. With the speedometer set for 255/50R17, an indicated 60 mph is 60.0 mph on 255/40R19.

Is this a safe swap?

Diameter difference −0.03%: under 1%

By overall diameter alone, 255/40R19 is a near match for 255/50R17; 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.

255/50R17 vs 255/40R19 differences
Measurement	255/50R17	255/40R19	Difference	% diff
Overall diameter	27.04 in (686.8 mm)	27.03 in (686.6 mm)	−0.01 in (−0.2 mm)	−0.03%
Sidewall height	5.02 in (127.5 mm)	4.02 in (102.0 mm)	−1.00 in (−25.5 mm)	−20.00%
Section width	10.04 in (255.0 mm)	10.04 in (255.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	84.95 in (2,157.6 mm)	84.92 in (2,157.0 mm)	−0.02 in (−0.6 mm)	−0.03%
Revolutions per mile	746	746	0	+0.03%

True speed with the speedometer calibrated for 255/50R17
Indicated	Actual on 255/50R17	Actual on 255/40R19
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 255/40R19 lowers the vehicle by 0.00 in (0.1 mm) at the axle (half the −0.2 mm diameter difference).

255/40R19 is 0.01 in shorter than 255/50R17 and the same width, a 0.03% difference in overall diameter.

With the speedometer calibrated for 255/50R17, an indicated 60 mph is actually 60.0 mph on 255/40R19, and revolutions per mile change from 746 to 746.

255/40R19 mounts on a 19-inch wheel, a plus-2 fitment from the 17-inch wheel of 255/50R17.

Size pages

Other comparisons with 255/50R17

Other comparisons with 255/40R19

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