TireSizesFinder

275/50R19 vs 305/40R20

305/40R20 is 0.22 in (5.6 mm) shorter than 275/50R19, a −0.74% diameter difference. With the speedometer set for 275/50R19, an indicated 60 mph is 59.6 mph on 305/40R20.

Is this a safe swap?

Diameter difference −0.74%: under 1%

By overall diameter alone, 305/40R20 is a near match for 275/50R19; 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: 275/50R19 (29.83 in) vs 305/40R20 (29.61 in)275/50R1929.83 in × 10.83 in305/40R2029.61 in × 12.01 in
Side profile and tread width, drawn to the same scale.
275/50R19 vs 305/40R20 differences
Measurement275/50R19305/40R20Difference% diff
Overall diameter29.83 in (757.6 mm)29.61 in (752.0 mm)−0.22 in (−5.6 mm)−0.74%
Sidewall height5.41 in (137.5 mm)4.80 in (122.0 mm)−0.61 in (−15.5 mm)−11.27%
Section width10.83 in (275.0 mm)12.01 in (305.0 mm)+1.18 in (+30.0 mm)+10.91%
Circumference93.70 in (2,380.1 mm)93.01 in (2,362.5 mm)−0.69 in (−17.6 mm)−0.74%
Revolutions per mile676681+5+0.74%
True speed with the speedometer calibrated for 275/50R19
IndicatedActual on 275/50R19Actual on 305/40R20Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.6 mph−0.4 mph
75 mph75.0 mph74.4 mph−0.6 mph

Ride-height change: 305/40R20 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.6 mm diameter difference).

305/40R20 is 0.22 in shorter than 275/50R19 and 30 mm wider, a 0.74% difference in overall diameter.

With the speedometer calibrated for 275/50R19, an indicated 60 mph is actually 59.6 mph on 305/40R20, and revolutions per mile change from 676 to 681.

305/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 275/50R19.

Size pages

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