TireSizesFinder

255/50R19 vs 255/40R21

255/40R21 is 0.01 in (0.2 mm) shorter than 255/50R19, a −0.03% diameter difference. With the speedometer set for 255/50R19, an indicated 60 mph is 60.0 mph on 255/40R21.

Is this a safe swap?

Diameter difference −0.03%: under 1%

By overall diameter alone, 255/40R21 is a near match for 255/50R19; 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: 255/50R19 (29.04 in) vs 255/40R21 (29.03 in)255/50R1929.04 in × 10.04 in255/40R2129.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
255/50R19 vs 255/40R21 differences
Measurement255/50R19255/40R21Difference% diff
Overall diameter29.04 in (737.6 mm)29.03 in (737.4 mm)−0.01 in (−0.2 mm)−0.03%
Sidewall height5.02 in (127.5 mm)4.02 in (102.0 mm)−1.00 in (−25.5 mm)−20.00%
Section width10.04 in (255.0 mm)10.04 in (255.0 mm)0.00 in (0.0 mm)0.00%
Circumference91.23 in (2,317.2 mm)91.21 in (2,316.6 mm)−0.02 in (−0.6 mm)−0.03%
Revolutions per mile6956950+0.03%
True speed with the speedometer calibrated for 255/50R19
IndicatedActual on 255/50R19Actual on 255/40R21Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph75.0 mph0.0 mph

Ride-height change: 255/40R21 lowers the vehicle by 0.00 in (0.1 mm) at the axle (half the −0.2 mm diameter difference).

255/40R21 is 0.01 in shorter than 255/50R19 and the same width, a 0.03% difference in overall diameter.

With the speedometer calibrated for 255/50R19, an indicated 60 mph is actually 60.0 mph on 255/40R21, and revolutions per mile change from 695 to 695.

255/40R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 255/50R19.

Size pages

Other comparisons with 255/50R19

Other comparisons with 255/40R21

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