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Tire sizes

305/55R20 — width without height on a 20-inch wheel

The metric code that gets nearest to a 33x12.50 in the dimension the arithmetic usually cannot follow.

Metric notation · Light truck (LT-metric)

Overall diameter
33.21 in
844 mm
Section width
12.01 in
305 mm
Sidewall height
6.60 in
168 mm
Aspect ratio
55%
sidewall as a share of width
Wheel diameter
20 in
the hole in the middle
Circumference
104.3 in
2650 mm
Revolutions per mile
607.3
geometric, not measured
Revolutions per km
377.4
geometric, not measured
Typical load index
108–129
2205–4079 lb per tire

LT-metric tires use a stiffer casing at a much higher reference inflation — Load Range C, D or E, meaning 50, 65 or 80 psi. The index band reflects the pressure the casing is rated to hold, not a larger tire.

The load-index range shown is the band this CLASS of size is typically produced in — not a list of what is in stock for this exact size today. Load index and speed symbol are printed on the sidewall of the specific tire you are holding, and the required minimum is on the placard of the specific vehicle you are fitting. Read both.

Nearest real sizes in imperial notation, same wheel

  • 33x12.50R2033.00 in tall-0.21 in
  • 35x12.50R2035.00 in tall+1.79 in
  • 37x12.50R2037.00 in tall+3.79 in

Compare any two sizes, including ones this site has no page for, in the comparison tool.

No vehicle in this catalogue is recorded on 305/55R20, as a factory size or an upgrade. It is a replacement and aftermarket code, and its interest lies in how close it gets to a tire that is listed on nine platforms.

Half an inch off a flotation 33, in width

The recurring complaint about metric near-33s is that they match the height and miss the width by more than an inch. This one does not.

305/55R20 33x12.50R20
Overall diameter 33.21 in 33.00 in
Section width 12.01 in 12.50 in
Sidewall 6.60 in 6.50 in
Revolutions per mile 607.3 611.2

0.21 in of height and 0.49 in of width. For comparison, 275/60R20 matches the flotation 33's height to a hundredth of an inch and is 1.67 in narrower; 285/60R20 is 0.46 in taller and 1.28 in narrower. No other metric code on this wheel comes within half an inch of the flotation tire in both dimensions at once.

The cost of that width in aspect ratio

Getting a 305 mm casing to roughly 33 in on a 20-inch wheel takes only 55 aspect points, because the percentage is being applied to a large number. The result is 6.60 in of sidewall — deeper, by a tenth of an inch, than the flotation 33's 6.50 in, despite the flotation tire being the wider of the two.

That is the same relationship every wide, low-aspect-number size demonstrates: a shape that reads as low-profile on paper can carry more casing than a shape that reads as conventional, provided the casing it is a percentage of is wide enough.

Its neighbours, and how little separates them

  • 275/60R20 — 32.99 in, 0.22 in shorter, 1.18 in narrower
  • 33x12.50R20 — 33.00 in, 0.21 in shorter, 0.49 in wider
  • 285/60R20 — 33.46 in, 0.26 in taller, 0.79 in narrower
  • 295/70R17 — 33.26 in, 0.05 in taller, on three inches less wheel

Four codes within half an inch of this one, and the tightest of them is on a completely different wheel diameter. Where the notations line up and where they part company is set out in the metric versus imperial reference.

Related

Class: Light truck (LT-metric). Every figure above is computed from the size code, not stored — see how these numbers are calculated.