Tire
There are many different sizes of tires. On car and truck tires, they are marked with 3 numbers and might look like: 225/60R16.  The first number is the width in millimeters of the tire at the widest point when it is mounted and inflated. The second number is the sidewall (side of the tire) height as a ratio or percentage of the width. The last number is the wheel diameter in inches.