TireSizesFinder

275/45R19 vs 245/40R21

245/40R21 is 0.03 in (0.7 mm) shorter than 275/45R19, a −0.10% diameter difference. With the speedometer set for 275/45R19, an indicated 60 mph is 59.9 mph on 245/40R21.

Is this a safe swap?

Diameter difference −0.10%: under 1%

By overall diameter alone, 245/40R21 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 245/40R21 (28.72 in)275/45R1928.74 in × 10.83 in245/40R2128.72 in × 9.65 in
Side profile and tread width, drawn to the same scale.
275/45R19 vs 245/40R21 differences
Measurement275/45R19245/40R21Difference% diff
Overall diameter28.74 in (730.1 mm)28.72 in (729.4 mm)−0.03 in (−0.7 mm)−0.10%
Sidewall height4.87 in (123.8 mm)3.86 in (98.0 mm)−1.01 in (−25.7 mm)−20.81%
Section width10.83 in (275.0 mm)9.65 in (245.0 mm)−1.18 in (−30.0 mm)−10.91%
Circumference90.30 in (2,293.7 mm)90.22 in (2,291.5 mm)−0.09 in (−2.2 mm)−0.10%
Revolutions per mile702702+1+0.10%
True speed with the speedometer calibrated for 275/45R19
IndicatedActual on 275/45R19Actual on 245/40R21Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 245/40R21 lowers the vehicle by 0.01 in (0.3 mm) at the axle (half the −0.7 mm diameter difference).

245/40R21 is 0.03 in shorter than 275/45R19 and 30 mm narrower, a 0.10% difference in overall diameter.

With the speedometer calibrated for 275/45R19, an indicated 60 mph is actually 59.9 mph on 245/40R21, and revolutions per mile change from 702 to 702.

245/40R21 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.