Aspect Ratio

In the context of automobiles, “aspect ratio” (偏平率) generally refers to the value printed on the tire: the ratio of the section height to the section width (tread width). The unit is a percentage.

The aspect ratio is shown on the sidewall, for example in “205/65R15 94H” — the 65 is the aspect ratio.

Omitted aspect ratio

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In the past, when many tires had an aspect ratio of 82, some tires were sold with the aspect ratio omitted (e.g. 145SR12). To replace an 82-aspect tire today, a tire with an aspect ratio of 80 is used. In practice, 80 and 82 aspect tires are often made to the same size.

偏平率 vs 扁平率

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Both 偏平率 and 扁平率 are widely used spellings.

By kanji meaning, 扁 (flat) looks more correct than 偏 (to lean). However, 扁平率 is a term describing how much a sphere has been squashed — a value close to 100% means a flatter ellipse. For tires, the number expresses the ratio of the section height, so the meaning is different. As tire terminology, 偏平率 is considered the correct term.