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CAR
TYRE PRESSURES, TYRE INFORMATION & TECHNICAL TERMS -
Learn
all you need to know about tyres:
Tread
The
tread is that portion of the TYRE that comes in contact with the
road. The tread is a thick rubber compound formulated to provide
a high level of traction that does not wear away too quickly. The
tread pattern is characterized by the geometrical shape of the grooves,
lugs, and voids. Grooves run circumferentially around the TYRE ,
and are needed to channel away water. Lugs are that portion of the
tread design that contacts the road surface. Voids are spaces between
lugs that allow the lugs to flex. Tread patterns feature non-symmetrical
lug sizes circumferentially in order to minimize noise.
Treads
are often designed to meet specific product marketing positions.
High performance TYRES have small void ratios to provide more rubber
in contact with the road for higher traction, but may be compounded
with softer rubber that provides better traction, but wears quickly.
Mud and snow TYRES are designed with higher void ratios to channel
away rain and mud, while providing better gripping performance.
When installing two new TYRES with a deep tread, they should be
placed in the rear to minimize the chance of oversteer.
Tread
lug
Tread
lugs provide the contact surface necessary to provide traction.
As the tread lug enters the road contact area, or footprint, it
is compressed. As it rotates through the footprint it is deformed
circumferentially. As it exits the footprint it recovers to its
original shape. During the deformation and recovery cycle the TYRE
exerts variable forces into the vehicle. These forces are described
as Force Variation.
Tread
void
Tread
voids provide space for the lug to flex and deform as it enters
and exits the footprint. Voids also provide channels for rainwater
to flow out of the footprint. Voids also provide space for mud and
snow to be channeled away from the footprint. The void ratio is
the void area of the TYRE divided by the entire tread area. Low
void areas have high contact area and therefore higher traction.
Rain
groove
The
rain groove is a design element of the tread pattern specifically
arranged to channel water away from the footprint. Rain grooves
are circumferential in most truck TYRES. Many high performance passenger
TYRES feature rain grooves that are angled from the center toward
the sides of the TYRE . Some TYRE manufacturers claim that their
tread pattern is designed to actively pump water out from under
the TYRE by the action of the tread flexing. This results in a smoother
ride in different types of weather.
Sipe
Tread
lugs often feature small narrow voids, or sipes, that improve the
flexibility of the lug to deform as it traverses the footprint area.
This reduces shear stress in the lug and reduces heat build up.
Wear
bar
Wear
bars are raised features located at the bottom of the tread grooves
that indicate excessive TYRE wear. When the tread lugs are worn
to the point that the wear bars connect across the lugs, the TYRES
are fully worn and should be taken out of service.
Contact
Patch
The
contact patch, or footprint, of the TYRE is the area of the tread
in contact with the road. This is the area that transmits forces
between the TYRE and the road via friction. The length-to-width
ratio of the contact patch will affect steering and cornering behavior.
Bead
The
bead is that part of the TYRE that contacts the wheel. The bead
is reinforced with steel wire, and compounded from high strength,
low flexibility rubber. The bead seats against the wheel tightly
to ensure that the TYRE holds air without leakage. The bead fit
is tight also to ensure the TYRE does not shift circumferentially
as the TYRE rotates.
Sidewall
The
sidewall is that part of the TYRE that bridges between the tread
and bead. The sidewall is reinforced with rubber and fabric plies
that provide for strength and flexibility. The sidewall transmits
the torque applied by the drive axle to the tread in order to create
traction. Sidewalls are molded with decorative ornamentation, government
mandated warning labels, and other consumer information.
Over
time, rubber degrades. Ford has recommended that TYRES be replaced
when they are 6 years old to prevent sudden failure, even if the
TYRE looks undamaged. In tropical climates, such as in Singapore,
TYRES degrade sooner than in temperate climates.
Shoulder
The
shoulder is that part of the TYRE at the edge of the tread as it
makes transition to the sidewall.
Inner
tube
Bicycle
TYRES and some passenger and truck TYRES are designed for use with
inner tubes. Inner tubes are torus shaped balloons made from a compound
impervious to air leakage. The inner tubes are inserted into the
TYRE and inflated to give the TYRE its final shape.
Wheel
TYRES
are mounted to wheels, or rims, that bolt to the drive axle. Automotive
wheels are either made from cast metal alloys, or stamped/welded
metal.
Valve
stem
The
valve stem is a tubular rubber shape with a metal valve used to
inflate the TYRE with air. Valve stems usually protrude through
the wheel for easy access for inflation. TYRES are inflated through
a valve, typically a Schrader valve on automobiles and most bicycle
TYRES, or a Presta valve on high performance bicycles. The rubber
in valve stems eventually degrades. Replacement on the valve stem
at regular intervals reduces the chance of failure.
TYRE
Pressure Monitoring System
There
are several types of designs to monitor TYRE pressure. Some actually
measure the air pressure and some make indirect measurements, such
as gauging when the relative size of the TYRE changes due to lower
air pressure.
Load
Rating
TYRES
are specified by the manufacturer with a maximum load rating. Loads
exceeding the rating can result in unsafe conditions that can lead
to steering instability and even rupture.
Inflation
pressure
TYRES
are specified by the manufacturer with a recommended inflation pressure
that permits safe operation within the specified load rating. Most
TYRES are stamped with a maximum pressure rating. For passenger
vehicles and light trucks, the TYRES should be inflated to what
the vehicle manufacturer specifies, which is usually located on
a decal just inside the driver's door.
Speed
rating
The
speed rating denotes the maximum speed at which a TYRE is designed
to be driven for extended periods of time. The ratings range from
99 mph (160 km/h) to 186 mph (300 km/h).
Rotation
TYRES
often exhibit irregular wear patterns once installed on a vehicle
and partially worn. TYRE rotation is the procedure of moving TYRES
to different car positions, such as front-to-rear, in order to even
out the wear, thereby extending the life of the TYRE.
Wheel
alignment
Once
mounted on the vehicle, the TYRE may not be perfectly aligned to
the direction of travel, and therefore exhibit irregular wear, often
quite substantial. A wheel alignment is the procedure for checking
and correcting this condition through adjustment of camber, caster
and toe angles. These settings also affect the handling characteristics
of the vehicle.
Retread
TYRES
that are fully worn can be re-manufactured to replace the worn tread.
Retreading is the process of buffing away the worn tread and applying
a new tread. Retreading is economical for truck TYRES because the
cost of the replacement is small compared to the cost of the TYRE
carcass. Retreading is less economical for passenger TYRES because
the cost is high compared to the cost of a new TYRE.
Flat
tyre
A flat
TYRE occurs when the TYRE deflates to the point that the metal of
the wheel comes to ground level. This can occur as a result of a
wear-and-tear, a leak, or more serious damage. A flat TYRE seriously
impairs the ability of the vehicle to be driven, requiring the vehicle
to be safely removed from the road, and the TYRE to be changed.
Continuing to drive a vehicle with a flat TYRE may result in damage
to the TYRE or the vehicle, and may put the occupants and other
vehicles in danger.
Aquaplaning
Aquaplaning
is the condition where a layer of water is present between the TYRE
and road. aquaplaning occurs when the tread pattern cannot channel
away water at a rate of speed to ensure a complete dry footprint
area. When aquaplaning occurs the TYRE loses traction and steering,
and creates a very unsafe driving condition. When aquaplaning occurs,
there is no responsiveness from the steering wheel. The correction
of this unsafe condition is to gradually reduce speed.
TYRE
Markings
DOT
Code- The DOT Code is an alphanumeric character sequence molded
into the sidewall of the TYRE for purposes of TYRE identification.
The DOT Code is mandated by the US Department of Transportation.
The DOT Code begins with the letters "DOT" followed by
a two numbers or letters plant code that identifies where it was
manufactured. The last four numbers represent the week and year
the TYRE was built. For example, the numbers 3197 means the 31st
week of 1997. The other numbers are marketing codes used at the
manufacturer's discretion. The DOT Code is useful in identifying
TYRES for recall.
E-Mark
All
TYRES sold in Europe after July 1997 must carry an E-mark. The mark
itself is either an upper or lower case "E" followed by
a number in a circle or rectangle, followed by a further number.
An "E" (upper case) indicates that the TYRE is certified
to comply with the dimensional, performance and marking requirements
of ECE regulation 30. An "e" (lower case) indicates that
the TYRE is certified to comply with the dimensional, performance
and marking requirements of Directive 92/33/EEC. The number in the
circle or rectangle denotes the country code of the government that
granted the type approval. The last number outside the circle or
rectangle is the number of the type approval certificate issued
for that particular TYRE size and type.
Mold
Serial Number
TYRE
manufacturers usually embed a mold serial number into the sidewall
area of the mold, so that the TYRE , once molded, can be traced
back to the mold of original manufacture.
TYRE
Use Classifications
TYRES
are classified into several standard types based on the type of
vehicle they serve. Since the manufacturing process, raw materials,
and equipment vary according to the TYRE type it is common for TYRE
factories to specialize in one or more
TYRE
types
High Performance
High
performance TYRES are designed for use at higher speeds. They feature
a softer rubber compound for improved traction, especially on high
speed cornering. The trade off of this softer rubber is lower tread
life.
High performance street TYRES sometimes sacrifice wet weather handling
by having shallower water channels to provide more actual rubber
tread surface area for dry weather performance. The ability to provide
a high level of performance on both wet and dry pavement varies
widely between manufacturers and even TYRE models of the same manufacturer.
This is an area of active research and development, as well as marketing.
Mud
and Snow
Mud
and Snow, or M+S, is a classification for winter TYRES designed
to provide improved performance under winter conditions compared
to TYRES made for use in summer. The tread compound is usually softer
than that used in TYRES for summer conditions, thus providing better
grip on ice and snow, but wears more quickly at higher temperatures.
TYRES may have well above average numbers of sipes in the tread
pattern to grip the ice.
Dedicated
winter TYRES will bear the "Mountain/Snowflake Pictograph"
if designated as a winter/snow TYRE by the American Society for
Testing & Materials. Winter TYRES will typically also carry
the designation MS, M&S, or the words MUD AND SNOW (but see
All-season TYRES, below).
Studded
TYRE
Some
winter TYRES may be designed to accept the installation of metal
studs for additional traction on icy roads. The studs also roughen
the ice, so providing better friction between the ice and the soft
rubber in winter TYRES. Use of studs is regulated in most countries,
and even prohibited in some locales due to the increased road wear
caused by studs. Typically, studs are never used on heavier vehicles.
Studded TYRES are used in the upper tier classes of ice racing.
Other winter TYRES rely on factors other than studding for traction
on ice, e.g. highly porous or hydrophilic rubber that adheres to
the wet film on the ice surface.
Some
jurisdictions may from time to time require snow TYRES or traction
aids (e.g. TYRE chains) on vehicles driven in certain areas during
extreme conditions.
Mud TYRES are specialty TYRES with large chunky tread patterns designed
to bite into muddy surfaces. The large open design also allows mud
to clear quickly from between the lugs. Mud terrain TYRES also tend
to be wider than other TYRES, to spread the weight of the vehicle
over a greater area to prevent the vehicle from sinking too deeply
into the mud.
All
Season
The
All Season TYRE classification is a compromise between one developed
for use on dry and wet roads during summer and one developed for
use under winter conditions. The type of rubber and the tread pattern
best suited for use under summer conditions cannot, for technical
reasons, give good performance on snow and ice. The all-season TYRE
is a compromise, and is neither an excellent summer TYRE nor an
excellent winter TYRE . They have, however, become almost ubiquitous
as original and replacement equipment on automobiles marketed in
the United States, due to their convenience and their adequate performance
in most situations. All-Season TYRES are also marked for mud and
snow the same as winter TYRES. Owing to the compromise with performance
during summer, winter performance is usually poorer than a winter
TYRE.
All Terrain
All-terrain
TYRES are typically used on SUVs and light trucks. These TYRES often
have stiffer sidewalls for greater resistance against puncture when
traveling off-road, the tread pattern offers wider spacing than
all-season TYRES to remove mud from the tread. Many TYRES in the
all-terrain category are designed primarily for on-road use, particularly
all-terrain TYRES that are originally sold with the vehicle.
Spare
TYRE
Vehicles
typically carry a spare TYRE , already mounted on a rim, to be used
in the event of flat TYRE or blowout. Minispare TYRES are smaller
than normal TYRES to save on trunk space, gas mileage, weight and
cost. Minispares have a short life expectancy, and low speed rating.
Run-Flat
TYRE
Several
innovative designs have been introduced that permit TYRES to run
safely with no air for a limited range at a limited speed. These
TYRES feature still load supporting sidewalls and often plastic
load-bearing inserts.
Heavy duty truck TYRES
Heavy
duty TYRES are also referred to as Truck/Bus TYRES. These are the
TYRE Sizes used on vehicles such as commercial freight trucks, dump
trucks, and passenger busses. Truck TYRES are sub-categorized into
specialties according to vehicle position such as steering, drive
axle, and trailer. Each type is designed with the reinforcements,
material compounds, and tread patterns that best optimize the TYRE
performance.
Off-the-Road
(OTR)
The
OTR TYRE classification includes TYRES for construction vehicles
such as backhoes, graders, trenchers, and the like; as well as large
mining trucks. These TYRES are built with a large number of reinforcing
plies to withstand severe service conditions and high loads. OTR
TYRES are used in rather low speed conditions.
Agricultural
The
agricultural TYRE classification includes TYRES used on farm vehicles,
typically tractors and specialty vehicles like harvesters. High
flotation TYRES are used in swampy environments and feature large
footprints at low inflation pressures.
Racing
NASCAR TYRES
Racing
TYRES are highly specialised according to vehicle and race track
conditions. This classification includes TYRES for top fuel dragsters,
oval track racers, jet-powered trucks, and monster trucks, as well
as the large-market race TYRES for Formula One and NASCAR.
TYRES
are specially engineered for specific race tracks according to surface
conditions, cornering loads, and track temperature. TYRES have also
been specially engineered for drifting. Racing TYRES are often engineered
to minimum weight targets, so TYRES for a 500 mile race may run
only 300 miles before a TYRE change. Some TYRE makers invest heavily
in race TYRE development as part of the company's marketing strategy
and a means of advertising.
Industrial
The
Industrial TYRE classification includes pneumatic and non-pneumatic
TYRES for specialty industrial vehicles such as skid loaders and
fork lift trucks.
Bicycle
This
classification includes all forms of bicycle TYRES, including racing
TYRES, mountain-bike TYRES, and snow TYRES.
Aircraft
Aircraft
TYRES are designed to withstand heavy loads for short durations.
The number of TYRES required for aircraft increase with the weight
of the plane. Aircraft TYRE tread patterns are designed to facilitate
stability in high crosswind conditions, to channel away water to
prevent hydroplaning, and for braking traction. Aircraft TYRES are
usually inflated with nitrogen gas in order to minimize the expansion
and contraction due to the extreme changes in temperature experienced
during flight. Dry nitrogen expands at the same rate as other dry
atmospheric gases, but common compressed air sources may contain
some moisture, which would increase the expansion rate with temperature.
Aircraft TYRES generally operate at high pressures, up to 200 psi
(13.8 bar) for airliners and higher for business jets.
Aircraft
TYRES also include heat fuses, which melt when a certain temperature
is reached. TYRES often overheat if maximum braking is applied during
a rejected takeoff or an emergency landing. The fuses provide a
safer failure mode, since the TYRE will no longer explode when overheated,
but deflate in a controlled way, thus minimizing damage to aircraft
or injury to people on the ground.
The
main purpose of requiring that an inert gas, such as nitrogen, be
used instead of air, for inflation of TYRES on certain transport
category airplanes is prompted by at least three cases in which
the oxygen in air-filled TYRES combined with volatile gases given
off by a severely overheated TYRE and exploded upon reaching autoignition
temperature. The use of an inert gas for TYRE inflation will eliminate
the possibility of a TYRE explosion. Federal Aviation Administration
14 CFR Part 25 [Docket No. 26147; Notice No. 90-7] RIN 2120-AD37
Use of Nitrogen or Other Inert Gas for TYRE Inflation in Lieu of
Air.
Motorcycle
There
are many different types of motorcycle TYRES
Sport Touring - These TYRES are generally not used for high cornering
loads, but for long straights, good for riding across the country.
Street - For sport bikes that are generally not going to be riding
aggressively. Riders of this type usually want TYRES that are going
to last a few more miles.
Sport Street - These TYRES are for aggressive street riders that
spend most of their time carving corners on public roadways. These
TYRES do not have a long life, but in turn have very good traction
in high speed cornering.
Track/Slick
TYRES - These TYRES are for track days or races. They have more
of a triangular form, which in turn gives a larger contact patch
while leaned over. These TYRES are not recommended for the street
by manufactures, and are known to have a shorter life on the street.
Due to the triangulation of the TYRE , there will be less contact
patch in the center, causing the TYRE to develop a flat spot quicker
when used to ride on straightaways for long periods of time.
TYRE
construction
Bias
TYRE construction utilizes body ply cords that extend diagonally
from bead to bead, usually at angles in the range of 30 to 40 degrees,
with successive plies laid at opposing angles forming a crisscross
pattern to which the tread is applied. The design allows for the
entire TYRE body to flex easily providing the main advantage of
this construction, a smooth ride on rough surfaces. This cushioning
characteristic makes for major disadvantages of a bias TYRES: increased
rolling resistance and less control and traction at higher speeds.
Belted
bias TYRE
A belted
bias TYRE starts with two or more bias-plies to which stabilizer
belts are bonded directly beneath the tread. This construction provides
smoother ride that is similar to the bias TYRE , while lessening
rolling resistance because the belts increase tread stiffness. However
the plies and belts are at different angles, which lessens performance
compared to radial TYRES.
Radial
TYRE
Radial
TYRE construction utilizes body ply cords extending from the beads
and across the tread so that the cords are laid at approximately
right angles to the centerline of the tread, and parallel to each
other, as well as stiff stabilizer belts directly beneath the tread.
The advantages of this construction include longer tread life, better
steering control, and lower rolling resistance. A disadvantage of
the radial TYRE is that it produces a harder ride at low speeds
on rough roads.
Solid
TYRE
Many
TYRES used in industrial and commercial applications are non-pneumatic,
and are manufactured from solid rubber and plastic compounds via
molding operations. Solid TYRES include those used for lawn mowers,
golf carts, scooters, and many types of light industrial vehicles,
carts, and trailers.
Semi-Pneumatic
TYRES
that are hollow, but are not pressurized have also been designed
for automotive use. The outer casing is rubber as in ordinary radial
TYRES, but the interior has special compressible polyurethane springs
to contribute to a comfortable ride. Besides offering run-flat capability,
the TYRES are intended to combine the comfort offered by higher-profile
TYRES (with tall sidewalls) with the resistance to cornering forces
offered by low profile TYRES. They have not yet been delivered for
broad market use.
TYRE
performance metrics
Tread wear
Friction
between the TYRE and the roadway causes the tread rubber to wear
away over time. Government standards prescribe the minimum allowable
tread depth for safe operation. There are several types of abnormal
tread wear. Poor wheel alignment can cause excessive wear of the
innermost or outermost ribs. Over inflation can cause excessive
wear to the center of the tread. Under inflation can cause excessive
wear to the outer ribs. TYRE manufacturers and car companies have
mutually established standards for tread wear testing that include
measurement parameters for tread loss profile, lug count, and heel-toe
wear. Also can be known as TYRE wear. See also TKPH below.
Dry
traction
Dry
traction is measure of the TYRE ’s ability to deliver traction,
or grip, under dry conditions. Dry traction increases in proportion
to the tread contact area. Dry traction is also a function of the
tackiness of the rubber compound.
Wet
traction
Wet
traction is measure of the TYRE ’s ability to deliver traction,
or grip, under wet conditions. Wet traction is improved by the tread
design’s ability to channel water out of the TYRE footprint
and reduce hydroplaning.
Force
Variation
The
TYRE tread and sidewall elements undergo deformation and recovery
as they enter and exit the footprint. Since the rubber is elastomeric,
it is compressed during this cycle. As the rubber deforms and recovers
it imparts cyclical forces into the vehicle. These variations are
collectively referred to as TYRE Uniformity. TYRE Uniformity is
characterized by Radial Force Variation (RFV), Lateral Force Variation
(LFV), and Tangential Force Variation. Radial and Lateral Force
Variation is measured on a Force Variation Machine at the end of
the manufacturing process. TYRES outside the specified limits for
RFV and LFV are rejected. In addition, TYRE Uniformity Machines
are used to measure geometric parameters including Radial Runout,
Lateral Runout, and Sidewall Bulge in the TYRE factory at the end
of the manufacturing process as a quality check.
Balance
When
a TYRE is rotated it will exert a centrifugal force characteristic
of its center of gravity. This cyclical force is referred to as
balance, or imbalance or unbalance. TYRES are checked at the point
of manufacture for excessive static imbalance and dynamic imbalance
using automatic TYRE Balance Machines. TYRES are checked again in
the auto assembly plant or TYRE retail shop after mounting the TYRE
to the wheel. Assemblies that exhibit excessive imbalance are corrected
by applying balance weights to the wheels to counteract the TYRE
/wheel imbalance.
To facilitate
proper balancing, most high performance TYRE manufacturers place
red and yellow marks on the sidewalls of its TYRES to enable the
best possible match-mounting of the TYRE /wheel assembly. There
are two methods of match-mounting high performance TYRE to wheel
assemblies using these red (Uniformity) or yellow (Weight) marks.
Centrifugal
Growth
A TYRE
rotating at high speed will develop a larger diameter due to centrifugal
forces that force the tread rubber away from the axis of rotation.
As the TYRE diameter grows the TYRE width decreases. This centrifugal
growth can cause rubbing of the TYRE against the vehicle at high
speeds. Motorcycle TYRES are often designed with reinforcements
aimed at minimizing centrifugal growth.
Rolling
resistance
Rolling
resistance is the resistance to rolling caused by deformation of
the TYRE in contact with the roadway. As the TYRE rolls, tread enters
the contact area and is deformed flat to conform to the roadway.
The energy required to make the deformation depends on the inflation
pressure, rotating speed, and numerous physical properties of the
TYRE structure, such as spring force and stiffness. TYRE makers
seek lower rolling resistance TYRE constructions in order to improve
fuel economy in cars and especially trucks, where rolling resistance
accounts for a high amount of fuel consumption.
Stopping
distance
The
use of performance oriented TYRES, which have a tread pattern and
rubber compounds designed to grip the road surface, usually has
slightly shorter stopping distances. However, specific braking tests
are necessary for data beyond generalizations.
TKPH
Ton
kilometre per hour (TKPH) is the measurement of the work load of
a TYRE and is used for monitoring its work so that it is not put
under undue stress which may lead to its premature failure. The
measurement's appellation and units are the same; it is not part
of the metric system even though it uses its base units. The recent
shortage and increasing cost of TYRES for heavy equipment has made
TKPH an important parameter in TYRE selection and equipment maintenance
for the mining industry.
For this
reason TYRE manufacturers of large earth-moving and mining vehicles
assign TKPH ratings to their TYRES based on their size, construction,
tread type, and rubber compound. The rating is based on the weight
and speed that the TYRE can handle without overheating and causing
it to deteriorate prematurely. The equivalent measure used in the
United States is ton mile per hour (TMPH).
References
1. ^ SAE. TKPH application. Retrieved on October 7, 2007.
2. ^ Bridgestone. How to use TKPH. Retrieved on October 7, 2007.
3. ^ Goodyear. New temperature prediction model improves on current
TKPH formula. C.Michael Hogan, Analysis of highway noise, Journal
of Water, Air, & Soil Pollution, Volume 2, Number 3, Biomedical
and Life Sciences and Earth and Environmental Science Issue, Pages
387-392, September, 1973, Springer Verlag, Netherlands ISSN 0049-6979
4. ^ http://www.safetyresearch.net/tires.htm
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