This Blog Further explains the construction, Manufacturing and other aspects that shape the performance of a tire. If you have not read about the various types of tires that exist. Please check out.
The structure of tire is dominated by the construction of Carcass. The carcass is the skeleton of the tire it is of three types-
- Cross-ply type- In this type, the ply cords are woven at an angle (30-40°) to the tire axis. There are two layers which run in the opposite direction. The cords are not woven or run side to side like in loom as it would result in rubbing of the two layers and produce heat which would damage the tire.
- Radial ply type- In this type, the ply cards run in the direction of the tire axis. Breaker strips are added to this structure in the circumferential direction. Breaker strips have flexible material but inextensible so that no change in circumference takes place with the change in the amount of air inside. Without the breaker strips, the radial plies would give very soft ride but there will not be any lateral stability. Breaker strips act as a girder in its own plane and provide directional stability.
- Belted bias type- This is the combination of the two types. The basic construction is the cross-ply over which run a number of breaker belts. These belts help to
- Restrict the stresses in the carcass and stabilize the tread area.
- Belts hold the tread against the road surface causing an increase of traction.
- Belt increase the resistance of tire to cuts and punctures.
Considerations in terms of tread design-
- Grip- It depends on the tread design and tread material. The grip for a particular tread pattern is affected by both mechanical and through friction. For better mechanical contact, the tread must have sharp edges that will engage the road, while for a good frictional contact tire must have a good drainage of water on the road, otherwise, the tire will aquaplane. Aquaplane refers to the floating of the tire on water film and lose contact with the ground. In some countries, there is a non-skid depth (NSD) that must be provided. Experimentally more narrow grooves provide better drainage than a small number of wide grooves.
- Noise- It depends on the tread material, various types of vibrations caused by roughness of road surface and distortion of tire carcass also produce noise. The noise comes from the leading edge of the tire block making contact with the road surface and the trailing edge snapping back as it breaks contact with the road surface. Therefore, winter tires are always noisier as they have more blocks. This source of noise is eliminated by providing intentional irregularities in the tread pattern by varying the size or shape of tread blocks.
- Wear- For less wear the tire must be designed such that individual element undergoes minimum distortion during running.
The ratio of tire section height to the tire section width. It is expressed in percentage. Lower aspect ratio gives better load carrying capacity, less wear, higher cornering power, and better performance at high speeds, but they give an uncomfortable ride because of less vertical flexibility.
Consider the code 145 SR- 13.
- 145 is the width of the tire.
- S is the speed rating of the tire.
- P- 150 kph
- Q- 160 kph
- R- 170 kph
- S- 180 kph
- T- 190 kph
- U- 200 kph
- H- 210 kph
- V- 240 kph
- W- 270 kph
- Y- 300 kph
- ZR- Over 240
- R signifies the radial construction.
- 13 inches is the diameter of the tire.
The internationally followed nomenclature is-
- Intended tire use (P for passenger).
- The width of the tire in mm.
- Aspect Ratio of the tire.
- Construction of tire.
- The diameter of the wheel rim on which the tire is fitted.
- Load Index.
- The speed rating of the tire.
Nitrogen is used for quite some time in tires. It helps to increase fuel efficiency. Nitrogen molecules being bigger than oxygen, seeps out slowly from tires. It also reduces the oxidation and results in longer tire life.
Wide Vs Narrow tires-
- Wider tires give better grip. This is not due to a bigger contact patch. If we keep the weight and tire pressure same and change the tires in the same vehicle, Contact patch area = weight on the single tire, which is same in both cases. The difference comes in the length that has to flex, in case of narrow tires, longer length has to flex which means that there will be relatively lesser time to cool off. Due to this reason, the narrow tire has to be made of hard rubber to resist the heating. The harder rubber has a lesser coefficient of friction and hence the grip decreases.
- Wider tires also perform better during cornering, wider tires have lower sidewalls which makes them more resistant to deforming under lateral load during cornering. It results in a more predictable and stable contact patch.
- The process of shifting from narrow to wide tires is called up-stepping. But following things must be taken care of-
- Overall tire diameter should be maintained. Otherwise, there will be an odometer and speedometer error.
- The wheel well diameter must be maintained.
Large bales of natural or synthetic rubber are fed to bale splitter which cuts the bales into smaller blocks of rubber. Then other compounding ingredients are added in proper composition, mixing is done in Banbury mixer after this the soft, masticated rubber compound is dropped in a mixing mill from which the rubber compound is taken out in form of sheets called masterbatch. Samples from the master batch are taken and tested in the laboratory to ensure proper quality. After this, vulcanizing agents are added and then mixed and converted into thin sheets called final stock.
The final stock is then softened on warning mills and then taken in continuous strips on a conveyer belt to other machines, where it is converted into treads, sidewalls, tubes etc. For making tire plies, rayon and nylon cords are dipped in a special liquid rubber compound and are tension dried under controlled conditions, this is called gum dipping. After this calendaring is done where the fabric is rolled into liners and then taken to a bias machine where it is cut across cords at a specified angle. These pieces are laid end to end and spliced into a continuous strip. The beads are made from a number of strands of copper plated high tensile steel wire, guided through a die where special insulation rubber is squeezed around and between separate strands. This insulated wire is then fed to bead winding machine where it is wound around a ring.
Various manufactured components are assembled in an assembly machine. It is called the green tire. Green tire further undergoes farming and vulcanizing processes before the final tire is ready.
Reviving an old worn tire to extend its life by adding new material is called retreading. The only part of the tire being affected is tread. A car tire can be retreaded once and the tire usually has a potential of having more than one life.
- Initial inspection to determine whether the tire can be retreaded or not.
- Removal of remaining unwanted material by buffing.
- Application of new tread and sometimes the sidewall veneer.
- Vulcanization is done in a mold or in an autoclave which can take a number of tires. This helps the newly applied tread to form a permanent chemical bond with the existing casing.
- Final inspection to rule out any defect.
- They are safe in countries where approval of retreaded tires is mandatory.
- It is economical to get a tire retreaded than to replace it.
- Eco-friendly, as retreading helps to save plenty of oil that is required in manufacturing a new tire.
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