Chapter XII - The rolling system

The rolling system ensures the movement of the car on public roads in safety conditions.

The wheels of the motor vehicle represent the rolling elements that serve to support the car on the surface of the ground and to obtain appropriate grip for movement.

Constructively, they are made of:

- tire: it is mounted on the rim and can have an air tube or not. The tire tread represents the shape of the grooves and crests applied on the tread band. The profile of the tires must have at least 4 mm depth. A flat profile with square shoulders offers good support in cornering;

The structure of the tires:

• the casing: it is the most important part of the tire, forming its skeleton. The casing takes over the large and complex stresses to which the tire is subjected during movement.
• the tread band: it offers a high level of grip and braking capacity. Due to their wear, their efficiency in providing traction is also limited.
• the bonding layer: it is the protective layer placed between the casing and the tread band. It has the role of ensuring a bond between the casing and the tread band and reduces the shocks produced during movement by the unevenness.
• the bead: it is the inner part of the tire which is included inside the rim.
• the mechanical insert: it ensures the durability and rigidity of the bead and is composed of steel wire fibers covered in rubber.
• the air chamber: it is a torus of natural or synthetic rubber, provided with a valve, called a valve through which pressurized air is introduced.
• the sidewall: it has the role of protecting the tire from external mechanical stresses.

- rim: from the point of view of the profile and configuration, it is adopted according to the category of the motor vehicle and according to the stresses of the wheel. For cars and trucks, rims with deep profile are used, these rims with recess can have open or closed ears which are shaped from the shoulder of the rim. The high ears provide the tire with strong lateral stability;

- the wheel disc: it is fixed to the rim by welding or riveting, and to the hub with bolts or studs. To reduce its weight and for ventilation, the disc is generally provided with holes. The disc starts from the hub towards the edge of the wheel towards the channel of the rim.

TO REMEMBER!

The markings on the sidewalls such as 215/45R 16 84V mean:

• 215 represents the width of the tire in millimeters.
• 45 represents the ratio between the height of the sidewall and the width of the tire.
• R represents the radial structure.
• 16 represents the inner diameter of the tire.
• 84 represents the maximum permissible load on one tire at maximum speed, this figure being the equivalent of the 500 kg load.
• V represents the speed index.