GarageCalc What 285/65R20 means
285 is the section width in millimeters (11.2 in). 65 is the aspect ratio: the sidewall is 65 percent of the width, so 285 × 0.65 = 185 mm (7.3 in). R is radial construction, and 20 is the wheel diameter in inches (508 mm). Stack two sidewalls on the wheel and you get the overall diameter: 508 + 2 × 185 = 879 mm, or 34.6 in.
A full marking adds a load index and speed rating after the size, for example 285/65R20 91V. Those two codes set how much weight and speed the tire is certified for; look them up in the load index chart and the speed rating chart.
Plus and minus sizing from 285/65R20
Similar diameter does not establish interchangeability. Follow the vehicle manufacturer's approved sizes; see Michelin's tire-size guidance.
No common size on a 19 or 21-inch wheel stays within 3 percent of 34.6 in, so 285/65R20 is best replaced like for like. The comparison calculator compares nominal dimensions for any candidate.
For the effect on road speed and distance, see our worked speedometer example. When maintaining this set, use the rotation pattern guide to check whether tire direction or different front and rear sizes restrict rotation.
Frequently asked questions
How tall is a 285/65R20 tire?
34.6 inches (879 mm) in overall diameter: the 20-inch wheel (508 mm) plus two 185 mm sidewalls. Actual dimensions depend on the tire model, tread depth, pressure and load; check the tire manufacturer specifications.
What is 285/65R20 in inches?
34.6 x 11.2 R20: 34.6 inches tall, 11.2 inches wide, on a 20-inch wheel. The sidewall is 7.3 inches and the circumference is 108.7 inches, so the tire turns 583 times per mile.
What tire sizes are equivalent to 285/65R20?
Within 3 percent of the same diameter on the same 20-inch wheel: 305/60R20 (-0.5%), 275/65R20 (-1.5%), 295/65R20 (+1.5%). These are nominal diameter comparisons, not approved replacements. Check vehicle-approved sizes, rim width, load and speed ratings, and clearance before changing size.
Can I use 295/65R20 instead of 285/65R20?
Nominal size comparison only: 295/65R20 is 1.5% taller (+13 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.1 mph. This does not confirm fitment. Check approved rim widths, load and speed ratings, and vehicle clearances. On the same wheel centerline, the extra nominal width uses about 0.20 in more space on each side, reducing clearance. Actual section width also depends on the tire model and rim width.