305/45R20 Tire Size Specifications & Compatible Vehicles

Overall Diameter

782.5 mm

Section Width

305 mm

Sidewall Height

137.3 mm

Circumference

2458.3 mm

Revs/Mile

655

Rim Diameter

20"

Alternative Tire Sizes

These tire sizes are within 3% overall diameter of 305/45R20 and may be used as replacements:

315/40R21 Safe 0.4% · +10mm · +1" rim 315/35R22 Safe 0.4% · +10mm · +2" rim 325/35R22 Safe 0.5% · +20mm · +2" rim 285/40R22 Safe 0.6% · -20mm · +2" rim 305/40R21 Safe 0.7% · same width · +1" rim 285/45R21 Safe 0.9% · -20mm · +1" rim 295/45R20 Safe 1.1% · -10mm · same rim 305/35R22 Safe 1.3% · same width · +2" rim 285/50R20 Safe 1.3% · -20mm · same rim 295/40R22 Caution 1.6% · -10mm · +2" rim 295/40R21 Caution 1.7% · -10mm · +1" rim 285/55R19 Caution 1.7% · -20mm · -1" rim

Understanding 305/45R20

The tire size 305/45R20 means the tire has a section width of 305mm, an aspect ratio of 45% (the sidewall height is 45% of the width), and fits a 20-inch rim.

Sidewall Height = 305 x 0.45 = 137.3 mm
Overall Diameter = (137.3 x 2) + (20 x 25.4) = 782.5 mm
Circumference = 782.5 x π = 2458.3 mm

With an aspect ratio of 45%, this is a low-profile tire. Low-profile tires offer sharper steering response and better cornering stability, but provide a firmer ride and are more susceptible to pothole damage. They are commonly found on sport sedans and performance vehicles.

Choosing Replacement Tires

When replacing 305/45R20 tires, verify the size matches your vehicle's tire placard (typically found on the driver's door jamb or in the owner's manual). The NHTSA Tire Ratings Search tool lets you look up manufacturer load and speed ratings for specific tires.

Key factors beyond size: load index (must meet or exceed the vehicle's requirement), speed rating (must match or exceed the original specification), and seasonal type (all-season, summer, or winter) based on your driving conditions. The U.S. Tire Manufacturers Association recommends replacing all four tires at once, or at minimum in pairs on the same axle.