More about tires
Tire sizes are expressed by the manufacturers with three sets of numbers:
Tread width – Aspect Ratio – Wheel diameter (e.g. 215 55 R16)
Automobile tires are described by an alphanumeric tire code (in American English)
or tyre code (in British English, Australian English and others), which is
generally molded into the sidewall of the tire. This code specifies the
dimensions of the tire, and some of its key limitations,
such as load-bearing ability, and maximum speed.
Sometimes the inner sidewall contains information not
included on the outer sidewall, and vice versa.
For more in dept information about tire size and tyre codes see Wikipedia