Your vehicle’s correct tyre size can usually be found in the owner’s manual or on a placard located inside the driver’s door jamb. It will be a combination of numbers and letters, like P215/65R16. The first number represents the tyre width in millimeters, the second is the aspect ratio (the tyre’s height as a percentage of its width), “R” indicates radial construction, and the last number is the diameter of the wheel in inches. Stick to the recommended size for optimal performance and safety.