Example: 195/55R16 87V

195 is the Width of the Tyre in millimeters

55 is the Profile (or Aspect Ratio) of the tyre.

Profile or Aspect Ratio is the distance (measured in percentage of the tyre Width) from the rim of the tyre to the base of the tyre tread.
e.g in this case the tyre;s profile is 55, meaning that the height of the tyre from the rim to the base of the the tyre tread if 55% of the tyre width (which is 195mm)

R indicates the tyres construction where the ‘R’ implies a Radial ply construction.

There are some tyres that are made with nylon cords instead and are sometimes referred to as ‘Nylon’ on ‘Bias’ tyres . In such tyres, the ‘R’ is replaced with either a ‘-‘or ‘x’ suggesting that the tyre is constructed using Nylon cords instead of Radial cords.

16 is the rim size or the diameter of the rim in inches. In this case a 16 inch rim.
87 is the load index.

The Load index a series of numbers assigned to certain loading capacities in Kilograms (KG) indicating the maximum loading capacity of the tyre. See the Load Index chart for other load ratings. 87 refers to 545 kg loading capacity per tyre.

V is a Speed rating symbol indicating maximum recommended speed in Km/h (kilometers per hour) for a particular tyre for safe operating assuming that the tyre is correctly fitted, inflated and is in good condition.

V refers to a speed rating of 240km/h maximum speed for this tyre are full load.