TireSizesFinder

275/45R19 vs 255/40R21

255/40R21 is 0.29 in (7.3 mm) taller than 275/45R19, a +1.00% diameter difference. With the speedometer set for 275/45R19, an indicated 60 mph is 60.6 mph on 255/40R21.

Is this a safe swap?

Diameter difference +1.00%: under 1%

By overall diameter alone, 255/40R21 is a near match for 275/45R19; 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: 275/45R19 (28.74 in) vs 255/40R21 (29.03 in)275/45R1928.74 in × 10.83 in255/40R2129.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
275/45R19 vs 255/40R21 differences
Measurement275/45R19255/40R21Difference% diff
Overall diameter28.74 in (730.1 mm)29.03 in (737.4 mm)+0.29 in (+7.3 mm)+1.00%
Sidewall height4.87 in (123.8 mm)4.02 in (102.0 mm)−0.86 in (−21.7 mm)−17.58%
Section width10.83 in (275.0 mm)10.04 in (255.0 mm)−0.79 in (−20.0 mm)−7.27%
Circumference90.30 in (2,293.7 mm)91.21 in (2,316.6 mm)+0.90 in (+22.9 mm)+1.00%
Revolutions per mile702695−7−0.99%
True speed with the speedometer calibrated for 275/45R19
IndicatedActual on 275/45R19Actual on 255/40R21Difference
30 mph30.0 mph30.3 mph+0.3 mph
60 mph60.0 mph60.6 mph+0.6 mph
75 mph75.0 mph75.7 mph+0.7 mph

Ride-height change: 255/40R21 raises the vehicle by 0.14 in (3.7 mm) at the axle (half the +7.3 mm diameter difference).

255/40R21 is 0.29 in taller than 275/45R19 and 20 mm narrower, a 1.00% difference in overall diameter.

With the speedometer calibrated for 275/45R19, an indicated 60 mph is actually 60.6 mph on 255/40R21, and revolutions per mile change from 702 to 695.

255/40R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 275/45R19.

Size pages

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