TYRE PARTS

Sidewalls

Sidewalls have two conflicting uses, one is to flex up and down acting as a shock

absorber during normal movement of the tyre on the road and to still be rigid enough to


bear the forces that come into play during normal running, braking, accelerating and


steering.


Several manufacturers have developed tyres that allow a vehicle to continue


moving despite loss of pressure. This is called Run Flat technology. One of the


approaches used by Bridgestone (RFT Series), Dunlop (DSST Series), Goodyear (EMT


Series) and Pirelli (Euphori) is the Reinforced tyre Sidewall. Whatever be the approach, it


must operate in tandem with the tyre pressure warning systems.


These tyres can be put on any rim. In these tyres the sidewall is reinforced with


inserts that are made of a highly resilient compound with high stiffness and low


hysteresis allowing the tyre to support the vehicle weight. New compounds are used in


the sidewall to prevent tyre destruction due to excessive flexing.
 

Casing plies

The term “ply” refers to a layer of fabric cords that is used to reinforce the tyre


casing. Without this reinforcement, on inflation the tyre will not have the required shape,


strength and structure. As stated earlier in a bias-ply tyre, two or four layers of cords are


wrapped at a 30 - 38 degree angle from bead to bead. And for stability reasons the layers


must be even with alternate direction of cords. And in a radial tyre the cords run at right


angles to the bead wires.
 
 

Rubber Breaker

Also called stabilizer belts or safety belts and are usually two in number. These


are belt layers under the tread section and are made of fiberglass, steel or Kevlar. These


reduce tread “squirm” on the road surface. In radial tyres also, the belts have to be


provided to prevent the tread area from “rolling” during cornering.


Another technology is the spiral winding technology.
 
 

Apex

The apex is also called the ”bead filler”. The apex stiffens the area just above the


beads and gives it strength and resilience during tyre mounting. Another device used in


some tyres is the rim flange protector that comes at the point where the wheel rim and


tyre meet.

                                                      Inner liner



The inner liner is a very critical component. It is a substitute for the tube used in


older style tyres. It is a double layer of synthetic gum rubber (butyl or halobutyl rubber)


that serves the purpose of sealing in the air and making the tyre tubeless. The main


functions of the rubber compound formulation for the inner liner are to provide the least


amount of air permeability (the butyl/halo – butyl rubber used here just does that)


possible and to strongly adhere to the body plies.






                                                                   Beads


Beads are shaped like hoops and are non - extensible. It has a high tensile and


high fatigue life steel wire (coated with brass) as it backbone. (Sometimes Kevlar is also


used). The bead fits against the wheel rim. Strands of steel are arranged sided by side in


the form of a ribbon and are coated with rubber for good adhesion. Special shapes like


pentagonal beads are used which provide extra stability under low inflation conditions


and prevents the bead from slipping off the rim bead seat.


Bead wires come in different configurations like weft less, cable beads and single


strand. Similar to steel cords used in steel belts of radial tyres, these are also transported


in hermetically sealed containers and appropriate precautions have to be taken to prevent


contamination by impurities like moisture and dust leading to corrosion and thus loss of


adherence to rubber while coating.


The main function of the bead loop is to support or anchor the body plies and to


prevent the wheel from slipping or rocking the rim.
 
                                                          Chafer



These narrow strips of reinforcing pliant fabrics are so called because they resist


the chafing from the wheel rim. Chafers add dimensional stability as well as gives high


adhesion to rubber.

Just like the Reinforced tyre Sidewall concept described above, Michelin uses a



concept called the PAX system. Like the former this also operates in line with the tyre


pressure monitoring systems. The rubber clip over the rim prevents the tyre from cutting


into the tyre when there is a loss of pressure. The clip element is several centimeters thick


and is of the same width as the tread.