Aspect Ratio

Tire aspect ratio is the sidewall height expressed as a percentage of the tire’s nominal section width. It is the second number in a metric tire size such as 225/65R17.

How aspect ratio is calculated

In 225/65R17, the section width is 225 millimetres and the aspect ratio is 65. The approximate sidewall height is therefore 65 percent of 225 millimetres, or 146.25 millimetres. The number is a ratio, not a direct height measurement.

Why aspect ratio matters

A lower aspect ratio usually means a shorter sidewall for a given width. Shorter sidewalls can provide a more direct steering response, while taller sidewalls can offer more cushioning and wheel protection. Actual behaviour also depends on tire construction, pressure, wheel width and vehicle suspension.

Changing tire size

Changing aspect ratio can alter overall tire diameter. That may affect speedometer accuracy, clearance, gearing and driver-assistance systems. Replacement sizes should keep overall dimensions and load capability within an appropriate range for the vehicle.

Related terms

Load index, section width, rim diameter and overall diameter.