305/30R20 — the lowest aspect ratio in this catalogue
The widest tire this catalogue puts on a car, and the shallowest shape it is built in.
Metric notation · Performance and ultra-high performance
- Overall diameter
- 27.20 in
- 691 mm
- Section width
- 12.01 in
- 305 mm
- Sidewall height
- 3.60 in
- 92 mm
- Aspect ratio
- 30%
- sidewall as a share of width
- Wheel diameter
- 20 in
- the hole in the middle
- Circumference
- 85.5 in
- 2171 mm
- Revolutions per mile
- 741.3
- geometric, not measured
- Revolutions per km
- 460.7
- geometric, not measured
- Typical load index
- 88–104
- 1235–1984 lb per tire
Low-profile sizes hold less air for their width, so the same vehicle weight needs a higher reference inflation. Extra Load construction is common in this class, and that is what lifts the index band — not any change in the casing size.
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+5.80 in
- 35x12.50R2035.00 in tall+7.80 in
- 37x12.50R2037.00 in tall+9.80 in
Compare any two sizes, including ones this site has no page for, in the comparison tool.
No vehicle record here lists 305/30R20 as a factory size or an upgrade. It belongs to the wide rear-fitment aftermarket, and it is the only 30-series code in the catalogue.
Widest casing, and not the tallest
12.01 in of section width is more than any other size on a wheel this site classes as a car wheel — 0.79 in more than the next widest, 285/35R20, and 2.36 in more than the narrowest, 245/35R20.
By height it is nowhere near the top. At 27.20 in it stands 0.65 in under 285/35R20 and 0.37 in under 275/35R20, and only 245/35R20 and 255/35R20 are shorter. Rank the group by width and this size is first; rank it by height and it is third of five.
The reason is entirely in the middle number. Thirty per cent of a 305 mm casing works out at 3.60 in of sidewall; thirty-five per cent of a 285 mm one works out at 3.93 in. A lower percentage of a bigger number is still a smaller number, and a size code offers no way to notice that without doing the conversion.
Which is the practical case for treating aspect ratio as a shape rather than a dimension. Two tires can only be compared on that figure when the widths it is a percentage of are also on the table. The aspect ratio reference works through the arithmetic.
What 3.60 inches of casing is doing
Between a 20-inch rim flange and the road there are three and a half inches of rubber here, which is the second-shallowest figure on any size in this catalogue. Only 245/35R19 and 245/35R20, at 3.38 in, are thinner.
That is the practical floor of the plus-sizing trade rather than an arbitrary limit. Adding another inch of wheel at this width would leave under three inches of casing, and the sizes to do it with are not produced.
Its height, found elsewhere
235/55R17 stands 27.18 in, three hundredths of an inch under this tire, on 9.25 in of section and 5.09 in of casing. 215/65R16 stands 27.00 in on 8.46 in and 5.50 in.
Both are ordinary saloon and crossover sizes. All three roll within a fifth of an inch of one another, and the widest of them carries barely two thirds of the narrowest one's casing depth.
Related
- 33x12.50R2033.00 in tall
- 35x12.50R2035.00 in tall
- 37x12.50R2037.00 in tall
Class: Performance and ultra-high performance. Every figure above is computed from the size code, not stored — see how these numbers are calculated.