Types of Tyres
- According to uses
- According to construction / Carcass Types
Types of Tyres (acc. to uses): [1]
1. Tyre with Tube:
Figure (1) shows the sectional view of a tyre, tube and part of the wheel rim. The inner tube is inflated with compressed air after the tyre along with the tube is mounted on the wheel rim.
 |
| Fig 1:Tyre-with-tube [1] |
It is not possible to fit the tyre on the rim along with a fully inflated tube. The inflation is done through a non-return ball valve fitted on the tube. A suitable perforation is provided on the rim for sticking out the valve projection from inside to the outside. Basically, this is not different from a bicycle tyre and tube construction. The inner tube after inflation fills all the space inside between the rim and the tyre and offers a good cushioning effect.
The tube inside is very vulnerable to piercing from outside by sharp objects like rough cut stones or nails. The tyre gets deflated all of a sudden and creates a situation for veering of the vehicle to one side and loss of steering control and serious accidents At high speeds the situation may cause dragging of the wheel rim on the road and constructional damage and deflection of the running gear.
2. Tubeless Tyre:
As the name indicates these tyres have no inflated inner tubes. The tyre is directly mounted on the rim. As the tyre alone has to withstand the internal air pressure, the section on the tyre is thicker than on an equivalent tyre with tube. The tyre is inflated with compressed air after mounting on the rim of the wheel through the non-return ball valve. Figure (2) presents a view of tubeless tyres.
 |
| Fig 2: Tubeless-tyre-c/s |
Advantages of tubeless tyres:
Tubeless tyres offer some significant advantages over tyres with inner tubes:
In case of a puncture, the compressed air from inside escapes gradually without causing appreciable damage. The vehicle can be braked and brought to rest well before anything serious could happen.
The air tube slithers inside a tyre, especially when it is under-inflated. The resulting friction between the outside surface of the tube and the inner surface of the tyre generates heat. This constant heating may lead to early degradation of the tube.
Tubeless tyres weigh less in general making the un-sprung mass less to the benefit of the suspension
The adhesion qualities of tubeless tyre are better. This contributes to better traction and steering control.
Tubeless tyres provide better fuel efficiency.
Carcass is the tyre body beneath the tread and
sidewalls; also called casing. Carcass or skeleton of the tyre have three types, On the basis of version of ply fabric layout;
- Cross ply or bais angle construction
- Radial ply construction
- Bais belted constrction
 |
| Fig 3: Carcass-or-construction: tyre [2] |
Two types of tyre construction are common – cross-ply and radial. Most passenger cars now use radial tyres, as do most 4-wheel-drives and heavy vehicles. The tyre is named after the particular type of carcass it contains as this is the main structure taking the stresses while in operation. [3]
 |
| Fig 4: Types-of-tyre-carcass/construction/ply-fabric |
The cross-ply tyre is the older form.
It is also called a bias-ply or conventional tyre. It is constructed of 2 or
more plies or layers of textile casing cords, positioned diagonally from bead
to bead.
The rubber-encased cords run or woven
at an angle of between 30 and 38 degrees to the centerline/tyre axis, with each
cord wrapped around the beads A latticed criss-crossed structure is formed,
with alternate layers crossing over each other and laid with the cord angles in
opposite directions.
There are two layers which run in opposite directions. However, the cords are not woven like wrap and weft of ordinary cloth because that would lead to rubbing of the two layers and thus produce heat which would damage the tyre material fig (4-a ).
This provides a strong, stable
casing, with relatively stiff sidewalls. However during cornering, stiff
sidewalls can distort the tread and partially lifting it off the road surface.
This reduces the friction between the road and the tyre. Stiff sidewalls can
also make tyres run at a high temperature. This is because, as the tyre
rotates, the cords in the plies flex over each other, causing friction and
heat. A tyre that overheats can wear prematurely.
2. Radial ply type
In this ply cords run in the radial
direction i.e. in the direction of the tyre axis. Over this basic structure,
run a number of breaker strips in the circumferential direction. The material
for the breaker strips must be flexible but inextensible, so that no change of
circumference takes place with change of the amount of inflation.
Without the breaker strips, radial plies would give very soft ride, but there will not be any lateral stability. The extensible breaker strip behaves like a girder in its own plane and provides the directional stability fig (4-b ).
Radial ply tyres have much more
flexible sidewalls due to their construction. They use 2 or more layers of
casing plies, with the cord loops running radially from bead to bead.
The sidewalls are more flexible
because the casing cords do not cross over each other. However, a belt of 2 or
more bracing layers must be placed under the tread. The cords of the bracing
layers may be of fabric, or of steel and are placed at 12, to 15 degrees to the
circumference line. This forms triangles where the belt cords cross over the
radial cords. The stiff bracing layer links the cord loops together to give
fore and aft stability, when accelerating, or braking and it prevents any
movement of the cords during cornering. The cord plies flex and deform only in
the area above the road contact patch.
There are no heavy plies to distort
and flexing of the thin casing generates little heat, which is easily
dispersed. A radial ply tyre runs cooler than a comparable cross-ply tyre and
this increase tread life. A radial tyre has less rolling resistance as it moves
over the road surface.
3. Bias Belted type
This is a combination of cross ply
& radial ply tyres. The basic construction is the bias ply over which run a
number of breaker belts, as shown in fig (4-c). The belts improve the characteristics of the bias-ply
tyre to a large extent. (1) the stresses in the carcass are restricted and the
tread area is stabilized by belts. This results in reduction of tread scrubbling
and thus appreciable increase in tyre life (2) the breaker belts hold the tread
flatter against the road surface, thus causing increase of traction and safety,
(3) the belts increase the resistance of the tyre against puncture.
Bias-belted tyres provide
a smoother ride and lower rolling resistance than bias tyres do.
Next Article: "Tyre Construction & Constitutes"
References:
[1] Automobile Engineering By Kamaraju Ramkrishna.
[2] Automobile Engineering By Ttti, © Tata McGraw-Hill Education.
[3] Trade of Motor Mechanic: Module 7: Unit 1: “Wheels
& Tyres” by SOLAS, In cooperation with: Subject Matter Experts; Martin
McMahon & CDX Global Curriculum Revision 2.2 16-01-07 © SOLAS 2013.
[4] Automotive Mechanics by Crouse & Anglin
[5] Automobile Engineering by Dr Kirpal Singh
[6] Automobile Engineering by Pitman
No comments:
Post a Comment