305/55R20 tire size

A 305/55R20 tire is 33.21 inches (843.5 mm) tall, 12.01 in (305 mm) wide and fits a 20-inch wheel. In inch notation it is roughly a 33.2x12.0R20 — a "33-inch" tire.

305/55R20 dimensions
Overall diameter	33.21 in	843.5 mm
Section width	12.01 in	305 mm
Sidewall height	6.60 in	167.8 mm
Circumference	104.33 in	2,650 mm
Revolutions	607.3 per mile	377.4 per km
Rim diameter	20 in	508.0 mm

Compare 305/55R20 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

−0.65%

60 mph on the speedometer = 59.6 mph actual

Within the ±3 % diameter range most tire fitters accept.

Ground clearance: −2.8 mm (−0.11 in)
Revolutions: 607 → 611 per mile

305/55R20 275/60R20

Side-by-side dimensions

	Current	New	Difference	%
Diameter	33.21 in	32.99 in	−0.22 in	−0.65%
Diameter	843.5 mm	838.0 mm	−5.5 mm	−0.65%
Width	12.01 in	10.83 in	−1.18 in	−9.84%
Width	305.0 mm	275.0 mm	−30.0 mm	−9.84%
Sidewall	6.60 in	6.50 in	−0.11 in	−1.64%
Sidewall	167.8 mm	165.0 mm	−2.8 mm	−1.64%
Circumference	104.33 in	103.65 in	−0.68 in	−0.65%
Revs per mile	607.3	611.3	+4.0	+0.66%

Speedometer error

Speedometer shows	Actual speed	Difference
20 mph	19.9 mph	−0.1 mph
30 mph	29.8 mph	−0.2 mph
40 mph	39.7 mph	−0.3 mph
50 mph	49.7 mph	−0.3 mph
60 mph	59.6 mph	−0.4 mph
70 mph	69.5 mph	−0.5 mph
80 mph	79.5 mph	−0.5 mph

Alternative sizes on the same 20-inch wheel

Sizes in use within ±3 % of the overall diameter of 305/55R20:

Plus and minus sizes for 305/55R20

Size	Wheel	Diameter	Difference
275/70R18	Minus 2 (18 in)	33.16 in	−0.15%
285/65R18	Minus 2 (18 in)	32.59 in	−1.87%
275/50R22	Plus 2 (22 in)	32.83 in	−1.15%
305/45R22	Plus 2 (22 in)	32.81 in	−1.21%
325/40R22	Plus 2 (22 in)	32.24 in	−2.93%

Nearby 20-inch sizes

Reading the 305/55R20 size

305 — section width in millimetres (12.01 in).
55 — aspect ratio: the sidewall is 55 % of the width, 167.8 mm.
R — radial construction (ZR on the sidewall means a high-speed rated radial; the dimensions are the same).
20 — fits a 20-inch diameter wheel.

The load index and speed rating (for example 91V) follow the size on the sidewall. They must meet at least the values on your vehicle's tire placard.