TireSizesFinder

275/55R19 vs 305/45R20

305/45R20 is 0.10 in (2.6 mm) shorter than 275/55R19, a −0.33% diameter difference. With the speedometer set for 275/55R19, an indicated 60 mph is 59.8 mph on 305/45R20.

Is this a safe swap?

Diameter difference −0.33%: under 1%

By overall diameter alone, 305/45R20 is a near match for 275/55R19; 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: 275/55R19 (30.91 in) vs 305/45R20 (30.81 in)275/55R1930.91 in × 10.83 in305/45R2030.81 in × 12.01 in
Side profile and tread width, drawn to the same scale.
275/55R19 vs 305/45R20 differences
Measurement275/55R19305/45R20Difference% diff
Overall diameter30.91 in (785.1 mm)30.81 in (782.5 mm)−0.10 in (−2.6 mm)−0.33%
Sidewall height5.95 in (151.3 mm)5.40 in (137.3 mm)−0.55 in (−14.0 mm)−9.26%
Section width10.83 in (275.0 mm)12.01 in (305.0 mm)+1.18 in (+30.0 mm)+10.91%
Circumference97.10 in (2,466.5 mm)96.78 in (2,458.3 mm)−0.32 in (−8.2 mm)−0.33%
Revolutions per mile652655+2+0.33%
True speed with the speedometer calibrated for 275/55R19
IndicatedActual on 275/55R19Actual on 305/45R20Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 305/45R20 lowers the vehicle by 0.05 in (1.3 mm) at the axle (half the −2.6 mm diameter difference).

305/45R20 is 0.10 in shorter than 275/55R19 and 30 mm wider, a 0.33% difference in overall diameter.

With the speedometer calibrated for 275/55R19, an indicated 60 mph is actually 59.8 mph on 305/45R20, and revolutions per mile change from 652 to 655.

305/45R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 275/55R19.

Size pages

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