Aspect ratio (65 in 215/65R15)

How to read it

USTMA defines the aspect ratio as the ratio of the tire’s section height to its Section width (215 in 215/65R15): at an aspect ratio of 60, the section height is 60% of the section width. It says aspect ratios are also called series or profile numbers and typically range from 30 to 80. On P215/65R15, the sidewall is about 140 mm tall: 65% of 215 mm. Yokohama says the higher the aspect ratio, the taller the sidewall.

Also searched as: second number on tire, sidewall height, tire profile.

Low-profile tires

NHTSA’s booklet says numbers of 70 or lower indicate a short sidewall, for improved steering response and better handling on dry pavement. Bridgestone’s replacement tire manual says low aspect ratio tires typically aid handling but have engineering trade-offs: they and their wheels may be more easily damaged by potholes, road hazards and curbs. It adds that P-metric sizes of 45 series and lower may be light load (LL) tires, which carry less than a standard load tire of the same size at the same pressure.

The same number on a different width

The aspect ratio is a proportion, so two tires with the same number can have sidewalls of different heights. Yokohama’s example at 70 percent is 129.5 mm; Carlisle’s ST175/80D13, at 80 percent of 175 mm, is 140 mm.