Radial & Cross ply tyres & Tyre Economy : Factor affecting tyre,Type of Tyre wear,Specification of Tyre.

Comparison of Radial and Cross Ply Tyre

1. Radial ply tyres have following advantages over cross ply tyre : 

i) Lower rolling resistance and hysteresis loss which means reduce power consumption.

(ii) Longer tread life: The extra-life may be upto 100% in some cases. This is on account of two factors,

   (a) In radial ply less heat build up.

   (b) The radial ply tyre does not squirm as it meets the Figure(a) and (b) shows the print of two type of tyre on road which in cross ply there is sideways slip which increase tyre wear.

 (iii) In radial ply, sidewall flexibility and treads region stiffness is more, the tendency of pattern grooves to slightly close in contact patch area which is not in cross ply. Thus the water removal efficiency and hence the braking efficiency on wet road is better in radial ply.

(iv) More comfortable ride at high speeds.

(v) Smaller slip angle and higher cornering power which gives better steering characteristics. The cornering force and self righting torque are higher for radial ply tyre.

(vi) During taking, a radial ply tyre has less tendency to distort and lift off the road from one side. Thus there is better contact of tyre and hence less tendency to skid while cornering in radial tyre.

2. Disadvantages of radial ply over cross ply tyre :

1. Heavier steering at low speed.

2. Uncomfortable ride at low speed.

3. Instability during comering.


Difference between radial ply and cross ply tyres

       Cross ply tyres → Radial ply tyres


1. Stiffness of tyre is more. → Stiffness of tyre is less.

2. Less comfortable due to more stiffness. → Gives comfort for speed 55 km/hr.

3. Tyre grip less on road. → Firm frictional grip with road. 

4. The first cost of cross-ply tyres is about 20% less than for radial-ply tyres. → Costlier than cross ply tyre.

5. Steering is easy. → Steering is harder.

6. Less tread life. → More tread life.

7. Plies are running diagonally opposite from bead to bead. → Plies are running radially straight from bead to bead.

8. Cross-ply tyres increase the amount of energy consumed while running, fuel consumption. → The more flexible casing of radial-ply compared to cross-ply tyres reduces the amount of energy consumed while running, so that saving in fuel consumption in the order of 5% is achieved.


Tyre Economy: Considerations in Tread Design

   Tread is a pattern design which is cut into the rubber and it helps to create traction between tyre and road. 

   The main consideration in tread the design of treads is grip, noise and wear. These will be discussed in detail in the following paragraphs.

a) Grip :

● The braking grip of a tyre depends upon two factors that are treads material and tread pattern. 

● In case or dry roads, the completely smooth tyre, no doubt, gives highest braking grip because it provides maximum area of contact with the road, however, in case wet road, its grip becomes almost negligible. 

● The grip for a particular tread pattern is affected mechanically as well as through road friction. For better mechanical contact, the tread must provide suitable sharp edges that will engage with the road. 

● While for a good frictional contact, it is very important that tyre must provide drainage of the water on the roa otherwise the tyre will aquaplane, that is float on the water film and loose contact with the ground.

● The various tread designs aim at satisfying these two basic requirements. Sufficiently wide grooves at the middle of tread serve to drain the road water.

● It has been found through experimentation that more number of comparatively narrower grooves provide better drainage as compared to small number of very wide grooves

(b) Noise:

● A part from the 'squall' peculiar tyre noise which depends upon the nature of the rubber compound used for the tyre treads. 

● Various types of vibrations caused by the roughness of the road surface and/or by the distortion of the tyre carcass alse produce noise 

● However, besides these, the type of tread pattern also contributes to tyre noise. It is seen that this source of noise is eliminated by providing intentional irregularities in the tread pattern by varying the size or shape of the tread blocks slightly.

(c) Wear:

● For less wear, the tyre tread must be such that the individual elements undergo minimum distortion during running.


Factors Affecting Tyre Life:

● The life of tyre is greatly reduced by under inflection, rapid stop, fast acceleration, road surface, misalignment and unbalance condition.

● Tyres wear quickly on sand and gravel roads whereas the tyre life is promoted to its maximum value by the concrete and asphalt roads. In addition to normal wear caused by evenly and smoothly worn tread.

● The tyre life can be greatly influenced by the factors as explain below.

Factors affecting tyre life

1. Atmospheric condition

2. The road surface condition

3. The Route

4. Type of work

5. Style of driving

6. Inflation Pressures and Load

7. Correct alignment of wheel

8. Proper maintenance


1. Atmospheric condition

● The heat generated by tyre does not affect by climate and seasonal condition but it affects by the way of heat dissipated to surrounding. At high temperature rubber gets softened result in decreases the abrasive resistance causes more thre wear.

● In rainy season or in wet condition water acts as a lubricant to rubber which reduces tyre wear but chances of puncture increases as rubber cut more easily in wet condition as it depend on nature it is unavoidable.

2 The road surface condition

● Concrete roads are greatly abrasive than tarred road as it is made from varying size of stone Gravel road and extremely smooth that effect wear.

3. The Route

 ● On straight roads tyre and tyre life reduces while winding road on a hilly areas, tyres wear much faster when to brake, change direction suddenly and accelerate continuously, even when speeds are relatively low. 

4. Type of work

● The time available for cooling tyre is less on long and high speed running. So continuous running reduces tyre life and it is unavoidable.

5. Style of driving

● The tyre life decreases with the increase of car speed.

● Fast starts, quick stop, high speed running or turning greatly reduce the tyre life while maximum tyre life and economy is promoted by conservative driving habits but this can be avoidable.

6. Inflation Pressures and Load 

● The sidewall of tyre is deflected due to overload as same as in under inflated. The frequency of side wall deflection increases with increases in speed of vehicle result in more heat generation causes more deflection. So tyre will damage or fails if it allowed for longer period. So tyre failure depends on amount of load, speed and distance travelled.

● The inflation pressure also influences on the tread which makes contact with the ground and the relationship between the tyre and the rim. Both these factors can increase uneven (and therefore, accelerated) tyre wear because the tread not makes contact with the surface of the road across its full area.

7. Correct alignment of wheel

● Due to excessive and too much camber the outer ribs will get warnt out. The wear on the inner side of the tyre treads is caused by the negative camber. The excessive wear on both the inner and outer area of the treads is caused due to excessive skidding on turn

● Due to toe-in, toe-out will affect the tyre life the scrubbing action on the road surface resulting in excessive wear if the toe in or toe out is not correct.

● Careless mounting /demounting of tyre causes bead damage exposing the bead wire. 

8. Proper maintenance

● Wheel alignment and balancing suspension settings which may change due to bad bump.


Types of Tyre Wear:

   (a) Under Inflation

   (b) Over Inflation

   (c) Poor alignment

   (d) Wheel imbalance

   (e) Fast turning on curve

   (f) Incorrect toe


(a) Under inflation : Both edges worn, squealing on curves, Under-inflection is the most usual cause of reduce tyre life. This causes the side of the tyres of its walls bend sharply as the wheel revolve. The cords eventually brake and the tyre blows out with the further revolving of the wheel. Tyre wear at the centrally excessively and less on outer edges. 

It is detrimental to life of tyre. It causes excessive flexing in irreparable damage to the tyre carcass or visible cracks on side wall, losc card inside casing

(1) More tread wear on the side

(2) Chances of rim bruises increases due to decrease resistance of the tyre to deflection

(b) Over Inflation :

1. Rapid tyre wear at centre only.

2. Abnormal stresses and strain in treat area causes separation of ply and tread cracking.

3. Decreases resistance to skidding because of reduction in contact surface of tyre trade with road.

4. Poor alignment : One side wear, saw toothed wear pattern.

5. Wheel imbalance : Treads worn unevenly with bald spots, cups or scallops. 

6. Fast turning on curve : Front tyre wear only.

7.Incorrect toe : Feathered edge.


Tyre Rotation :

● Tyre rotation is the practice of moving the wheels and tyres of an automobile from one position to another, to ensure even tyre wear. Even tyre wear is desirable to extend the useful life of a set of tyres. The weight on the front and rear axles differs which causes uneven wear.

● Tyre Rotation means to rotate tyres from open wheel to another wheel as per manufacturer 's guidelines as shown in the figure.

Justification :

    In order that all the tyres wear uniformly. It is recommended that tyres be rotated after fixed intervals. Generally after every 8000 kilometers of operation. The advantages of tyres wearing uniformly are: As wear reduces a tyres tread depth, if all the tyres wear at the same rate, all of them would respond to the driver's input equally maintaining the cornering and handling characteristics. To increase tyre life tyre position should be changed at each service.


Specification of Tyre : (Designation of Tyre)

● The tyres are specified and designated by the nominal size of their sectional width and rim diameter. They are marked as:

● Tyre life and performance are determined by factor like tyre load. Inflation pressure, driving habit and vehicle maintenance.

Example

P2QS/75R15 as specified above indicate passenger car tyre with sectional width 205 mm having aspect ratio of 75 and radial ply rating of 15 inch wheel diameter.

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