This process involves specially-formulated materials and internal construction that varies according to the intended use. At Bridgestone, each step is designed to ensure every tyre is made with the same renowned attention to quality.
Various grades of natural and synthetic rubber are mixed with carbon black, sulphur and chemical products to meet specific requirements. This master batch is then formed into rubber sheets.
The rubber is re-heated and fed through extruders, where the tread and sidewalls are formed from two different rubber compounds. The extruders produce a continuous sheet, which is cut to specific tyre lengths.
Spinning cords such as rayon, nylon, steel and polyester are woven into sheets and coated with rubber (called calendaring). The sheets are cut into specific sizes and used for casing and cap plies, while steel cords are used for the belts.
The bead core is formed by aligning, and then coating, plated steel wires with rubber. It’s then wound on a coil to form bead rings, which provide a specific diameter and strength for a particular tyre.
The inner liner, body plies and sidewalls are placed on the building drum. The bead rings are positioned, the ply edges are wrapped around the bead core and the sidewalls are moved into position. The tyre is shaped by inflating the rubber and applying sidetread rubber, two steel belts and a cap ply to make a "green" tyre.
The tyre is placed in a curing press for between 10 and 15 minutes at a specific pressure and temperature. This creates the tyre’s final size, shape and tread.
Excess rubber is removed and the tyre is trimmed to order.
Each tyre is visually and electronically inspected for balance, quality and uniformity.