TireSizesFinder

235/50R18 vs 255/40R19

255/40R19 is 0.22 in (5.6 mm) shorter than 235/50R18, a −0.81% diameter difference. With the speedometer set for 235/50R18, an indicated 60 mph is 59.5 mph on 255/40R19.

Is this a safe swap?

Diameter difference −0.81%: under 1%

By overall diameter alone, 255/40R19 is a near match for 235/50R18; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 235/50R18 (27.25 in) vs 255/40R19 (27.03 in)235/50R1827.25 in × 9.25 in255/40R1927.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
235/50R18 vs 255/40R19 differences
Measurement235/50R18255/40R19Difference% diff
Overall diameter27.25 in (692.2 mm)27.03 in (686.6 mm)−0.22 in (−5.6 mm)−0.81%
Sidewall height4.63 in (117.5 mm)4.02 in (102.0 mm)−0.61 in (−15.5 mm)−13.19%
Section width9.25 in (235.0 mm)10.04 in (255.0 mm)+0.79 in (+20.0 mm)+8.51%
Circumference85.61 in (2,174.6 mm)84.92 in (2,157.0 mm)−0.69 in (−17.6 mm)−0.81%
Revolutions per mile740746+6+0.82%
True speed with the speedometer calibrated for 235/50R18
IndicatedActual on 235/50R18Actual on 255/40R19Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.5 mph−0.5 mph
75 mph75.0 mph74.4 mph−0.6 mph

Ride-height change: 255/40R19 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.6 mm diameter difference).

255/40R19 is 0.22 in shorter than 235/50R18 and 20 mm wider, a 0.81% difference in overall diameter.

With the speedometer calibrated for 235/50R18, an indicated 60 mph is actually 59.5 mph on 255/40R19, and revolutions per mile change from 740 to 746.

255/40R19 mounts on a 19-inch wheel, a plus-1 fitment from the 18-inch wheel of 235/50R18.

Size pages

Other comparisons with 235/50R18

Other comparisons with 255/40R19

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.