Tire sizes

127 sizes, each one a size that is actually manufactured. There is no page for an arithmetic result nobody sells.

The catalogue is deliberately bounded. There are thousands of arithmetically valid size codes and a page for each would be a directory nobody reads and Google eventually stops crawling. What is here are the sizes that come off real vehicles and out of real catalogues.

Each page computes its dimensions from the size code rather than storing them, which is why the figures match the calculators exactly. Each also names the nearest genuinely-sold size in the other notation on the same wheel, which is usually the actual question behind the visit.

How the groups below work

Sizes are grouped by the class of tire they are produced as, because that is what determines the load-index band they are sold in — and load index is the constraint people miss. A 265/70R17 built as a passenger tire and a 265/70R17 built as a light-truck tire are the same shape and are not the same tire.

The band shown on each group is what that class is typically produced in. It is not a claim about any particular tire: load index and speed symbol are printed on the sidewall of the one you are holding, and the minimum you need is on the placard of the vehicle you are fitting.

If the size you want is not here

Type it into the comparison tool. The parser reads both notations and any wheel diameter, and the arithmetic is identical whether or not a page exists.

What a size page contains

The computed dimensions first: overall diameter, section width, sidewall height, aspect ratio, circumference, and revolutions per mile in both miles and kilometres. Then the class band, and the reason that class sits where it does. Then the nearest genuinely-sold sizes in the other notation on the same wheel, with the diameter difference of each — which is the question most visits are really about.

Then the platforms recorded with that size, if there are any, and the comparisons involving it. Then prose about that size specifically: where it came from, what it substitutes for, and the particular traps it carries.

Two depths, and why

Some sizes have a great deal that is true of them alone — a history, a substitution they are famous for, a conversion argument that follows them around. Those get a full page.

Others are perfectly real sizes that people genuinely buy and about which there is very little to say beyond the accurate numbers. Those get a shorter page: answer-first prose over the same computed panel, linking to the tool and up to the class.

That split is deliberate. The alternative — writing seven hundred words about every size in the catalogue — produces a hundred pages of the same sentences with the numbers changed, which is worse than a short honest page in every respect that matters.

A note on the numbers

Everything on a size page is computed from the code. Nothing is stored, so nothing can quietly disagree with the calculators. What that also means is that these are geometric figures, and a real tire is not a geometric object: measured diameters vary between manufacturers, and a loaded tire rolls on a smaller radius than its free radius. The methodology page sets out exactly where the arithmetic stops matching the rubber.

Passenger touring

A passenger tire's load index tracks its air volume, and volume tracks section width and sidewall height. Sizes in this class sit in the band that carries a typical two-tonne car with its rated payload across four tires.

Performance and ultra-high performance

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.

Crossover and SUV

Crossovers are heavier than the cars they share size families with, so the same nominal size is produced at a higher index for SUV fitment than for passenger fitment. Two tires wearing the same size code can carry materially different loads.

Light truck (LT-metric)

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.

Flotation (imperial)

Flotation sizes are almost always LT construction, so they share the light-truck band. Speed symbols run low because the aggressive tread patterns these sizes are sold in are rated against heat build-up, not against sustained high speed.