TireSizesFinder

245/55R19 vs 305/40R20

305/40R20 is 0.00 in (0.1 mm) shorter than 245/55R19, a −0.01% diameter difference. With the speedometer set for 245/55R19, an indicated 60 mph is 60.0 mph on 305/40R20.

Is this a safe swap?

Diameter difference −0.01%: under 1%

By overall diameter alone, 305/40R20 is a near match for 245/55R19; 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: 245/55R19 (29.61 in) vs 305/40R20 (29.61 in)245/55R1929.61 in × 9.65 in305/40R2029.61 in × 12.01 in
Side profile and tread width, drawn to the same scale.
245/55R19 vs 305/40R20 differences
Measurement245/55R19305/40R20Difference% diff
Overall diameter29.61 in (752.1 mm)29.61 in (752.0 mm)0.00 in (−0.1 mm)−0.01%
Sidewall height5.31 in (134.8 mm)4.80 in (122.0 mm)−0.50 in (−12.7 mm)−9.46%
Section width9.65 in (245.0 mm)12.01 in (305.0 mm)+2.36 in (+60.0 mm)+24.49%
Circumference93.02 in (2,362.8 mm)93.01 in (2,362.5 mm)−0.01 in (−0.3 mm)−0.01%
Revolutions per mile6816810+0.01%
True speed with the speedometer calibrated for 245/55R19
IndicatedActual on 245/55R19Actual on 305/40R20Difference
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: 305/40R20 does not change the vehicle at the axle (half the −0.1 mm diameter difference).

305/40R20 is the same height as 245/55R19 and 60 mm wider, a 0.01% difference in overall diameter.

With the speedometer calibrated for 245/55R19, an indicated 60 mph is actually 60.0 mph on 305/40R20, and revolutions per mile change from 681 to 681.

305/40R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 245/55R19.

Size pages

Other comparisons with 245/55R19

Other comparisons with 305/40R20

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