22 August 2010

RADIAL TYRE vs BIAS TYRE



RADIAL TYRE vs BIAS TYRE


A Pneumatic Tyre is a toroidal shaped flexible high performance composite membrane capable of containing air or fluid under pressure when mounted on a suitable rim




A tire (or tyre in British English) is a ring-shaped covering that fits around a wheel to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground. The word itself is derived from the word "attire", referring to the dressing of the wheel.





The fundamental materials of modern tires are rubber and fabric along with other compound chemicals. Their constructive make-up consists of the tread and the body. The tread provides traction while the body ensures support. Before rubber was invented, the first versions of tires were simply bands of metal that fit around wooden wheels in order to prevent wear and tear. The most recent and popular type of tire is pneumatic, pertaining to a fitted rubber based ring that is used as an inflatable cushion and generally filled with compressed air. Pneumatic tires are used on many types of vehicles, such as bicycles, motorcycles, cars, trucks, earthmovers, and aircraft.








BASIC REQUIREMENTS OF A PNEUMATIC TYRE











1) CUSHION THE RIDE


2) LOAD CARRYING


3) TRANSPORT THE LOAD



5) DEVELOP CORNERING FORCE



6) ECONOMICE PERFORMANCE










DESIGNING THE TYRE FOR BASIC REQUIREMENTS







LOAD: Taken by the air pressure - needs strength in the radial direction





CUSHIONING : Imparted by the air Influenced by the ability of the tyre membrane to deform radially





TRANSPORT: Traction, braking, road forces acting circumferentially in the contact area .Needs strength in the circumferential direction in the contact area.





CORNERING: Ability to develop cornering forces to counteract centrifugal forces .Needs excellent grip with ability to undergo lateral deformation





DURABILITY: Adequate flex fatigue properties and wear resistance to give economic life.






SPECIAL REQUIREMENTS




Ø Rolling Resistance


Ø Directional Stability


Ø Wet Traction


Ø Cut/Bruise/Stone Penetration Resistance


Ø Less Noise


Ø Excellent Uniformity And Balance


Ø Puncture Resistance


Ø High Speed Capability


Ø Run Flat Capability


Ø Whether Resistance


Ø Re treadability


Ø Cost


Ø Mileage Etc. …..



THREE DIMENSIONAL PERFORMANCE CAPABILITY OF A TYRE




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Tyre Size Designations




Bias Tyres



10.00-20




Where 10.00 - Nominal section width in inches


- Indicates bias tyre


20 - Nominal rim diameter in inches




7.50-16




Where 7.50 - Nominal section width in inches


- Indicates bias tyre


16 - Nominal rim diameter in inches






Radial Tyres




145/70TR12


Where 145 - Nominal section width in mm.


70 - Aspect ratio


Aspect ratio - ratio of section height to section width


T - Speed rating, 190 kmph.


R - Indicates radial tyres


12 - Nominal rim diameter in inches




9.00R20


Where 9.00 - Nominal section width in inches.


R - Indicates radial tyres


20 - Nominal rim diameter in inches






Classification of Tyres

a. Based on construction




Bias :




Tyres where the fabric cords run from one bead to another at an angle with respect to the centerline of the tyre.




Radial :




The cords on the tyre runs from one bead to another bead at 90 ° with respect to the centerline

of the tyre and with low angle belts for strength in circumferential direction.




Bias belted:




Bias tyres with low angle belts.






Bias angle:




Bias Angle : The angle which the cords in the tyre makes with respect to the centerline of the tyre is the most important parameter in the bias tyre.




The higher the angle the better the load carrying capacity - equivalent radial tyres requires a much lower Number of plies compared to a bias tyre.




The lower the angle the better the speed capabilities and The handling characteristics,



b. Based on application




  1. Passenger
  2. LCV
  3. Truck
  4. Farm - Rear Tractor (Flotation ,self cleaning ,directional)
  5. Aero - Pure rib, nitrogen inflation
  6. OTR etc.




C. Tube type or tubeless




Tubeless tyres will have better riding comfort than tube type tyres and the overall tyre weight will be lesser than tyre & tube weight in a tube type tyre.




Tubeless tyres will have higher bead seat taper compared to the tube type tyres.






D. Based on tread pattern






  • Rib tyres - Front application designed for


    • better handling.
    • Grooves and sipes are for water
    • channeling to avoid -aquaplaning.





* Lug tyres - Rear Application (drive wheel)


o designed for better traction.




* Semilug tyres - Front or rear application


o designed for bad roads and


o hilly terrains.

RIB TYPE






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LUG TYPE




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SEMI LUG TYPE


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Tire construction (Radial)









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Basic Overview of Tyre Building





Tyre Manufacturing

Process Stages of Building a Modern Radial Tyre





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The major steps in tyre manufacturing


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Material Preparation


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Textile Calendering Steel Calendering





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Steel Calendering





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Extrusion - Preparation of Treads and Sidewalls



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Bead Production






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Tyre Assembly Machine







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Curing Press / Mould






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CarcassBuilding



Bead wires are set at the applicators. Bead joint has to be in the right place to avoid tyre imbalance



Inner Liner

Inner liner is set at the drum and rotated around the drum at one turn. The joint is cut with a hot knife. Inner liner is set end to end so that the diagonal cutting seam is at the top. The ends are joined manually.


Body Ply: Mounting


Cord ply ends are set at the drum and rotated around the drum at one turn. The cord is cut by hand with a join of 2-5 overlapping wires. The join is pressed carefully together at the edges.










Bead Wire Mounting and Turn-Up


Bead wire mounting and turn-up is done automatically. Bead wire applicators bring the beads to the carcass. Edges are turned up with bladders over the beads and stitched tightly.



Sidewall Mounting and Joining

Sidewall ends are set at the drum and rotated around the drum at one turn. Sidewall is set end to end and the seam is fastened together manually.




Tread Package
Steel belt tables go down on the drum automatically. Steel belt is joined by cutting it with a hot knife and setting the ends together.



Cap Ply: Mounting and Joining
The ends of the nylon cap ply, is set at the drum in the middle of the steel belts. Bandage is wound on top of the steel belts 1-2 times. The bandage is cut with scissors.



Tread Mounting

Tread is pulled onto the drum automatically. Tread is set end to end and joined automatically.




First and Second Stage Coupling
Carcass (1st stage) and tread (2nd stage) packages are joined automatically. The carcass is set at the flanges of the carcass drum, pressurised, fastened to the tread package and stitched together.

Green Tyre

After building the green tyre it is transferred to the painting machine, where anti-blemish chemicals are applied.


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In a radial tyre plycords run from bead to bead in a radial manner and are protected with dual steel belts, which makes tread very stiff. But in bias tyre plycords run diagonally and are protected with nylon breakers


Bias-Ply History



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In 1898, the Goodyear Tire and Rubber Company discovered the process of vulcanizing rubber. To strengthen and mold the rubber, a casing of reinforced layers or plys of rubberized fabric cords are embedded into the rubber. Each subsequent layer is laid in alternating diagonal pattern bias to the bead cord. The degree of the bias varied between manufactures, running between 30 to 55 degreesto the bead cord.






For the next 60 years, bias-ply tires ruled the roads of America and gradually evolved from cotton cord belts in 1915, to rayon cord in the 1930 s, and then to nylon cords in 1943. Improved technology changes to bias-ply designs were introduced in 1954 with the advent of tubeless tires on Packard built cars, which fast became the standard on all automobiles there after.






In 1959, steel corded tires were introduced, followed by fiberglass corded tires in 1963, all based on the bias-ply design. The level of bias-ply tire design has remained pretty much unchanged since around 1965 when radial tires started showing up in dealer show rooms.






The main advantage of bias-ply tires is in its load carrying capabilities in relation to tire size. A smaller bias-ply tire can carry more load than a radial tire of similar size. The drawbacks are higher friction, equating to higher tire temperatures which results in faster wear. Also, the tread contact area (the area were tread meets pavement) is smaller and since the sidewall and tread area are constructed of one material, cornering affects the contact area more than on radial designed tires





Radial Tire History




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Michelin first introduced steel-belted radial tires in Europe in 1948. Radial tires are so named because the ply cords radiate at a 90 degree angle from the bead cord, and the casing is strengthened by a belt of steel fabric that runs around the circumference of the tire. In radial tire design the ply cords are made of nylon, rayon, or polyester.




In 1966, Michelin struck a deal with Sears to manufacture radial tires for sale under the Allstate label and within four years Sears was selling one million units per year. In the mid-1960s, B.F. Goodrich embraced radial technology as a means to win market share from its larger rivals, and the company introduced the first American-made radial in the mid-1960s and supported the launch with the Radial Age advertising campaign in 1968.




The August 1968 Consumer Reports awarded its top two spots to radials and documented the new technology s longer life, increased safety, handling and economy relative to even top-of-the-line bias-ply tires.




The advantages of radial tires include longer tread life, better steering characteristics, and less rolling resistance, which increases gas mileage. On the other hand, radials have a harder riding quality, and technologically are more complex than bias-ply tires, so they cost more to produce








ADVANTAGES OF RADIAL TYRES OVER BIAS TYRES

1 . Radial is an efficient engineering design.

1. Bias is a compromise design.
2. Not realising the full potential of the fabric reinforcement
3. In radial tyre, the sidewall work independently of tread whereas in a bias tyre they work in sympathy.


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Consider "x" kg is the BS of fabric. Then for a bias tyre, the factor forcarrying the load is given by"x sin ø" which is always much less than "x" as bias angle is around 38-45°. For a radial tyre it is "x sin90 = x"

2. 80-100% INCREASE IN MILEAGE

* No contact patch distortions
* No pantographic motions inside the tyre structure
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* No shuffling of tread elements. Shuffling of tread elementswith road surface results in abrasion. Lateral stiffness and circumferential stretch resistance of radial belt coupled with supple sidewall practically eliminates shuffling or scuffing with road surface.


3. Overall fuel efficiency up by 5-7% for car tyres and up 10% for truck tyres. (This is more pronounced at high speed)


1. Lower rolling resistance. Rolling resistance is the retarding force acting on a free rolling tyre opposite to the direction of rotation. Rolling resistance of a radial tyre is 15-20% less than that of a corresponding bias tyre.
2. Less internal friction.
3. No shuffling of tread elements
4. Cooler running
5. Radial has lower volume of materials

4. Excellent traction and braking on both wet and dry roads.

1. No de-stabilisation of contact patch
2. Higher contact area
3. More uniform pressure distribution.
4. Stiff belts . No deformation of tread in the direction of travel results in efficient transmission of tractive and braking torques.
5. Uninterrupted drainage channels.


5. Safe high speed cornering

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Develops high cornering force (capable of higher lateral deformation due to supple sidewall) and reduced slip angle .
Slip angle - When a pneumatic tyre is subjected to lateral forces (curve, effect of cross wind etc.), the mid plane of the tyre automatically diverges from the actual direction of vehicle motion. The angle between the direction of motion and the mid plane of the tyre is called slip angle.


The angle between thedirection in which thetyre, and thereforethe car, is pointingand actually travelingis known as the Slip Angle


This can be increased or decreased by the driver turning the steering wheel. In normal condition this angle relates approximately linear to the amount of side force developed generated by tyre.


Lateral deformations do not destabilise the contact patch whereas in a bias tyre the outer edge lifts while negotiating a curve leads to reduced contact area which leads to instability..




6. Improved riding comfort.



1. Supple and independently flexible sidewall.
2. Sooth transmission of road shocks.
3. The response lag of a bias tyre makes the ride uncomfortable at high speed.

7. Excellent high speed capability.


1. Less internal shear
2. Generates less heat and hence can sustain high speed..
3. Thinner casing radiates heat fast.


8. Improved endurance life and retreadability.


1. Less internal shear and compression
2. Generates less heat and hence less degradation..
3. Thinner casing radiates heat fast.
4. Radial dispositioning of carcass cords lowers compressive flexing which enhances the endurance life.


9. Runs quieter.


1. Majority of the noise is taken care in the tread pattern




10. Excellent impact resistance.
1. Supple sidewall absorbs road shocks better.


2. High strength belt resist breakage

11. Improved puncture and run flat resistance.

1. Radial tyres rolls over the object and not drags over it.
2. No peristalsis or pantographic motions to drive the object in to the tyre structure.
3. Stiff belt prevents penetration
4. In tubeless tyres, slow rate of air loss gives sufficient warning time.


12. Excellent impact resistance.
1. Supple sidewall absorbs road shocks better.
2. High strength belt resist breakage


13. Improved puncture and run flat resistance.


1. Radial tyres rolls over the object and not drags over it.
2. No peristalsis or pantographic motions to drive the object in to the tyre structure.
3. Stiff belt prevents penetration
4. In tubeless tyres, slow rate of air loss gives sufficient warning time.


14. Reduced vehicle maintenance

15. Reduction in vehicle weight.


DISADVATAGES OF RADIAL TYRES


* Heavier steering at parking speeds due to lateral stiffness of the belt.
* Sidewall damages by external objects due to high flexing of the sidewall
* Harsher low speed ride with steel belted tyres .










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Conclusion





The main advantage of bias-ply tires is in its load carrying capabilities in relation to tire size. A smaller bias-ply tire can carry more load than a radial tire of similar size. The drawbacks are higher friction, equating to higher tire temperatures which results in faster wear. Also, the tread contact area (the area were tread meets pavement) is smaller and since the sidewall and tread area are constructed of one material, cornering affects the contact area more than on radial designed tires.




The advantages of radial tires include longer tread life, better steering characteristics, and less rolling resistance, which increases gas mileage. On the other hand, radials have a harder riding quality, and technologically are more complex than bias-ply tires, so they cost more to produce.

























































































2 comments:

Nassim Dhaher said...

very good comparison, thanks for sharing.

Nassim Dhaher said...

very good comparison , thanks for sharing.

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