305/55R20 tire size

A 305/55R20 tire is 33.2 inches (844 mm) tall and 12.0 inches (305 mm) wide, and fits a 20-inch wheel. In inch sizing it is about a 33.2x12.0R20.

Overall diameter33.21in844 mm

Drawn to scale from the nominal size.

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Size	Diameter	Difference	Width	Sidewall	Wheel
275/70R18	33.2″	−0.2%	10.8″	7.6″	18″
33x12.50R15	33.0″	−0.6%	12.5″	9.0″	15″
33x12.50R17	33.0″	−0.6%	12.5″	8.0″	17″
33x12.50R18	33.0″	−0.6%	12.5″	7.5″	18″
33x12.50R20	33.0″	−0.6%	12.5″	6.5″	20″
275/60R20	33.0″	−0.7%	10.8″	6.5″	20″
285/75R16	32.8″	−1.1%	11.2″	8.4″	16″
305/70R16	32.8″	−1.2%	12.0″	8.4″	16″
305/45R22	32.8″	−1.2%	12.0″	5.4″	22″
295/55R20	32.8″	−1.3%	11.6″	6.4″	20″
285/70R17	32.7″	−1.5%	11.2″	7.9″	17″
265/70R18	32.6″	−1.8%	10.4″	7.3″	18″

Within 3% of the original diameter is the range most tire shops treat as a direct swap. Check load index and clearance too.

305: Section width: 305 mm (12.0 in) from sidewall to sidewall.
55: Aspect ratio: the sidewall is 55% as tall as the tire is wide, 168 mm (6.6 in).
R: Radial construction, used by almost every modern tire.
20: Fits a 20-inch wheel.

305/55R20 is about 33.2 inches tall and 12.0 inches wide, on a 20-inch wheel, roughly a 33.2x12.0R20 in inch sizing.

Yes. At 33.2 inches it is sold and fitted as a 33-inch tire.

275/70R18, 33x12.50R15, 33x12.50R17 are the closest common sizes, all within 0.6% of its diameter, so the speedometer stays close to accurate.

35x12.50R20 is 5.4% taller, so at an indicated 60 mph you would really be doing 63.2 mph. Compare 305/55R20 and 35x12.50R20.

About 607 per mile (377 per km), from a 104.3-inch circumference.