More than 5000 years ago the Sumerians invented the wheel. As the centuries passed the wheel was continually refined. Then in 1845 Robert William Thomson was granted a patent in England on an “air tube device” the forerunner of the modern pneumatic tire. This invention lay unused until the end of the 19th century.
The pneumatic tire we’re-invented’ in 1888 and began to achieve wide application. After nearly a century of use tires have made possible the evolution of a sophisticated personal transportation system.
But what is a tire? To most people a tire is a rubber doughnut. Geometrically a tire is a torus. Mechanically a tire is a flexible membrane pressure container. Structurally a tire is a high performance composite. Chemically a tire consists of materials from long-chain macromolecules. These various facets of a tire and their interrelationships will be discussed in this book.
Functions of a Pneumatic Tire
Fundamental to a discussion of tires is a description of the basic functions required of a pneumatic tire. These may be summarized:
(1) Have load-carrying capacity
(2) Provide cushioning ability
(3) Transmit driving and braking torque
(4) Produce cornering force
(5) Supply road-holding ability
(6) Provide dimensional stability
(7) Provide adequate mileage
(8) Provide steering response
(9) Consume minimum power
(10) Have minimum noise and vibration
(11) Be durable and safe
All, the listed functions essential to a system of locomotion have never been satisfactorily fulfilled except by a pneumatic tire. This is basically due to the unique deformability and damping characteristics of the tire structure.
The range of tire applications seems unlimited. Aircraft for example are equipped with tires even though there is an unwanted weight penalty and even though the tires do not function for 99 percent of vehicle operation. But during the remaining time spent in taking off and landing tires are essential and no substitute has been developed.
Tire Requirements
The basic functions of a tire can be generally grouped into the three areas of (a) vehicle mobility (b) performance and integrity and (c) esthetics and comfort. Each of these areas comprise many different tire requirements that must be considered in engineering a tire.
Tire Requirements
- TRACTION
- TREAD-WEAR
- DURABILITY
- RIDE
- HANDLING
- NOISE
- ROLLING
- RESISTANCE
- BRUISE RESISTANCE
- CUT RESISTANCE
- UNIFORMITY
- STATIC-LOADED
- RADIUS
- FLATSPOTTING
- OVERTURNING
- MOMENT
- DIMENSIONS
- TRACKING
- IMPACT
- RESISTANCE
- FORCE VARIATION
- THUMP
- CHIPPING
- HYDROPLANING
- PITCH
- FLATNESS
- RUMBLE
- HEAT GENERATION
- SEPARATION
- ASPECT RATIO
- STOPPING ABILITY
- STANDING WAVE
- GROWTH
- PUNCTURE
- RESISTANCE
- RIM CHAFING
- DRAG
- HARSHNESS
- FLEET DURABILITY
- SUPPLENESS
- CRACKING
- STONE RETENTION
- NIBBLING
- SLIP
- CUSHIONING
- CORNERING
- ABILITY
- FIRST HARMONIC
- RUNOUT
- SIZE FACTOR
- FLOTATION
- LOPE
- JOINT SLAP
- REVOLUTIONS
- PER MILE
- ENVELOPING
- STIFFNESS
- WOBBLE
- RESPONSE
- CONNICITY
- HIGH SPEED
- SIPING
- DEFLECTION
- BURST
- OZONE
- RESISTANCE
- PRESSURE RISE
- BUCKLING
- SNOW AND ICE
- PLUNGER
- WHINE
- INTEGRITY
- FUEL ECONOMY
- FATIGUE
- RESISTANCE
- RUNNING
- TEMPERATURE
- LATERAL PULL
- COOL RUNNING
- STEER EFFECT
- ROLLING RADIUS
- STABILITY
- FOOTPRINT
- SQUEAL
- TMPH
- ROUGHNESS
- ALIGNING TORQUE
- MEAN GROUND
- CONTACT PRESSURE
- PROFILE
- LOAD CARRYING
- CAPACITY
- VIBRATION
- ANALYSIS
- ROAD HAZARD
- RESISTANCE
- CHUNKING
- BALANCE
- MOISTURE
- RESISTANCE
- WEATHER
- RESISTANCE
- SHAKE
- NONSKID
- INFLATION
- PRESSURE
- SPRING RATE
- HOP
- TREAD PRESSURE
- BEAD DURABILITY
- DIRECTIONAL
- CONTROL
- SLIP ANGLE
- SKID RESISTANCE
- EVEN WEAR
- BEAD UNSEATING
- CORNERING
- STIFFNESS
- PITCH TONE
- TORQUE
- DAMPING
- POWER
- CONSUMPTION
Basic Tire Types
There are three basic types of tires.
First is the bias angle or cross ply tire. In this construction the reinforcing cords extend diagonally across the tire from bead to bead. The bias angle of the cord path to the centerline of the tire is generally in the range of 25 to 40 degrees. The cords run in opposite directions in each successive layer (or ply) of reinforcing material resulting in a crisscross pattern. This type has been a standard construction for years.
Second is the radial tire. In this construction the plies of reinforcing cords extend transversely from bead to bead. On top of the plies (under the tread) is an inextensible belt composed of several layers of cords. The belt cords are low angle (10 to 30 degrees) and act to restrict the 90-degree carcass plies. Increased sidewall bulging is characteristic of radial tires. Radial tires made their commercial appearance in the late 1940’s and first became popular in Europe.
The third design is the bias/belted tire which consists of a bias angle carcass with a circumferentially restricting belt. In the bias/belted tire the carcass angle is generally maintained between 25 and 45 degrees and the belt angle between 20 and 35 degrees.
In addition the angle of the belt is about 5 degrees less than the angle to the carcass. This tire is the latest of the basic tire types and was commercially introduced in 1967 More than 500 million tires are produced annually worldwide.
About half are made in the USA. Of all the tires being produced in the USA today (passenger truck etc.) it is estimated that 50 percent are bias 10 percent are radial and 40 percent are bias/belted. Worldwide (including the USA) the figures are estimated as 50 percent bias 25 percent radial and 25 percent bias/belted.
The development of new technologies for tire production is also very important, some manufacturers such as Hankook are developing innovations to improve the performance of tires.
Tire Components
These can be described as follows:
Tread: The tread is the wear-resistant component of the tire in contact with the road. The tread has to be designed for tread wear resistance traction silent running and low heat buildup.
The tread is normally composed of a blend of oil-extended SBR and polybutadiene elastomers (natural rubber is often used in large tires) that have been compounded by adding carbon black oils curative ingredients and other chemicals and pigments. A compounded elastomer is popularly called “rubber.” The composition of the rubber the cross sectional shape of the tread the number of ribs and grooves and the tread design are important in determining the wearing quality traction and running temperature of the tire.
Ribs: The ribs are the circumferential rows of tread rubber in direct contact with the road surface. Designs are molded into the ribs for traction noise suppression etc.
Grooves: The grooves are the circumferential channels between the tread ribs and are essential for traction directional control cool-running properties etc. Tread wear indicators are molded into the bottom of the tread grooves. These indicate when the tire should be replaced.
Sidewalls: 1 his sidewalls are the portion of the tire contour between the beads and the tread that primarily control ride and support characteristics. The term sidewall is sometimes specifically used to refer to the rubber covering that protects the carcass from curb damage. Sidewall rubber is compounded for high flex and weather resistance.
Shoulders: The shoulders are the upper portion of the sidewall just below the tread edge. Shoulder design affects tire heat behavior and cornering characteristics.
Beads: The beads are composed of high-tensile steel wire formed into inextensible hoops. The bead functions to anchor the plies and to hold the assembly on the rim of the wheel. The shape or contour of the bead conforms to the flange of the wheel to prevent the tire from rocking or slipping on the rim.
Plies: The plies are layers of cord fabric extending from bead to bead and are the reinforcing members of the tire. The plies are turned up around the bead thereby locking the bead into the tire carcass.
Belts: The belts are narrow layers of tire cord material directly under the tread in the crown of the tire. The belts are lower in angle than the carcass plies and act to restrict the carcass plies. Due to their high lateral stiffness the belts permit the tire to resist deformation in the footprint. Belts should be differentiated from breakers which are sometimes used in the crown of the tire. Breakers have nearly the same angle as the carcass plies but do not restrict the carcass plies.
Liner: The liner is a thin layer of rubber on the inside of the tire to contain the compressed air.
Chafers: The chafers are narrow strips of material placed around the outside of the bead to protect the cord plies against wear and cutting of the rim distribute the flexing above the rim and prevent the penetration of moisture and dirt into the tire.
Tire Materials
A tire is a “wonder” of the chemical industry. The components of a tire are nearly all fabricated from synthetic materials. The USA tire industry annually consumes approximately 6.5-billion pounds of tire cord elastomers carbon black oils chemicals pigments and other materials.