Tread
The tread is the part of the tire which comes in contact with the road surface. The tread is a thick rubber, or rubber/composite compound formulated to provide an appropriate level of traction that does not wear away too quickly. The tread pattern is characterized by the geometrical shape of the grooves, lugs, voids and sipes. Grooves run circumferentially around the tire, 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 (or non-uniform) lug sizes circumferentially in order to minimize noise.
Treads are often designed to meet specific product marketing positions. High performance tires 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.[citation needed] Mud and snow (M&S) tires are designed with higher void ratios to channel away rain and mud, while providing better gripping performance.
[edit] Treadwear
The treadwear grade describes how long the tire manufacturer expects the tire to last. A Course Monitoring Tire (the standard tire that a test tire will be compared to) has a rating of "100". If a manufacturer assigns a treadwear rating of 200 to a new tire, they are indicating that they expect the new tire to have a useful lifespan that is 200% of the life of a Course Monitoring Tire. In general, manufacturers tend to overstate the treadwear of their tires in an effort to create the impression that their tires last a long time. The ability of manufacturers to report their own numbers makes comparison of treadwear ratings between companies useless. Ratings may still be useful within a manufacturer's own line of tires.
[edit] 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 tire exerts variable forces into the vehicle.[citation needed] These forces are described as Force Variation.[citation needed]
[edit] Tread void
 | The factual accuracy of this section is disputed. Please see the relevant discussion on the talk page.(April 2008) |
Tread voids provide space for the lug to flex and deform as it enters and exits the footprint. Voids also provide channels for rainwater, mud, and snow to be channeled away from the footprint. The void ratio is the void area of the tire divided by the entire tread area. Low void areas have high contact area and therefore higher traction on clean, dry pavement.
[edit] Rain groove
| | The factual accuracy of this section is disputed. Please see the relevant discussion on the talk page.(April 2008) |
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 tires. Many high performance passenger tires feature rain grooves that are angled from the center toward the sides of the tire.[citation needed] Some tire manufacturers claim that their tread pattern is designed to actively pump water out from under the tire by the action of the tread flexing.[citation needed] This results in a smoother ride in different types of weather.[citation needed]
[edit] 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.[citation needed] Sipes also provide greater traction in icy conditions.
[edit] Wear bar
Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tire has reached its wear limit. When the tread lugs are worn to the point that the wear bars connect across the lugs, the tires are fully worn and should be taken out of service.[3]
[edit] Contact patch
The contact patch, or footprint, of the tire, is merely the area of the tread which is in contact with the road surface. This is the area which transmits forces between the tire and the road via friction. The length-to-width ratio of the contact patch will affect steering and cornering behavior.[citation needed]
[edit] Bead
The bead is that part of the tire which contacts the rim on the wheel. The bead is reinforced with steel wire, and compounded from high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air without leakage. The bead fit is tight, to ensure the tire does not shift circumferentially as the wheel rotates. The width of the rim in relationship to the tire are a factor in the handling characteristics of an automobile because the rim supports the tire's profile.
[edit] Sidewall
The sidewall is that part of the tire 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. The sidewall, in conjunction with the air inflation, also supports the load of the vehicle. Sidewalls are molded with manufacturer-specific detail, government mandated warning labels, and other consumer information, and sometimes decorative ornamentation.
Over time, rubber degrades. Ford[citation needed] has recommended that tires be replaced when they are 6 years old to prevent sudden failure, even if the tire looks undamaged. In tropical climates, such as in Singapore, tires degrade sooner than in temperate climates.[citation needed] Tires on seldom-used trailers are at the greatest risk of age-failure but some tires are built to withstand idleness. This is usually done by using nylon reinforcement. In the past rayon was used in tires but it ages quite badly.
[edit] Shoulder
The shoulder is that part of the tire at the edge of the tread as it makes transition to the sidewall.
[edit] Inner tube
Amost all bicycle tires, some motorcycle tires, and many tires for large vehicles such as passengers, semi trucks, and tractors are designed for use with inner tubes. Inner tubes are torus shaped balloons made from a material initially impervious to air leakage. The inner tubes are inserted into the tire and inflated to retain air pressure.
[edit] Wheel
Tires are mounted to wheels that bolt to the hub. The inside edges of the tire are held on the wheel's rim. Automotive wheels are typically made from pressed and welded steel, or composite of lightweight metal alloys, such as aluminium or magnesium. These alloy wheels may be either cast or forged.
[edit] Valve stem
The valve stem is a tube made of steel or rubber with a metal valve used to inflate the tire with air. Valve stems usually protrude through the wheel for easy access for inflation. Tires are inflated through a valve, typically a Schrader valve on automobiles and most bicycle tires, or a Presta valve on high performance bicycles. The rubber in valve stems eventually degrades. Replacement of the valve stem at regular intervals reduces the chance of failure.
[edit] Tire pressure monitoring system
Tire pressure monitoring systems are electronic systems which monitors the tire pressures on individual wheels on a vehicle, and alerts the driver when the pressure goes below a warning limit. There are several types of designs to monitor tire pressure. Some actually measure the air pressure, and some make indirect measurements, such as gauging when the relative size of the tire changes due to lower air pressure. These systems are becoming mandatory in countries such as the United States.[citation needed]
[edit] Inflation pressure
Tires are specified by the vehicle manufacturer with a recommended inflation pressure, which permits safe operation within the specified load rating and vehicle loading. Most tires are stamped with a maximum pressure rating (for USA only). For passenger vehicles and light trucks, the tires should be inflated to what the vehicle manufacturer recommends, which is usually located on a decal just inside the driver's door, or in the vehicle owners handbook. Tires should not be inflated to the pressure on the sidewall; this is the maximum pressure, rather than the recommended pressure.[4]
If tire pressure is too high, the tire contact patch is reduced. This decreases rolling resistance; however, ride comfort is reduced, traction is reduced and stopping distance is increased.
If tire pressure is too low, the tire contact patch is increased. This increases rolling resistance and increases friction between the road and tire. This can lead to tire overheating, premature tread wear, and tread separation in severe cases. As per the NHTSA test: http://www.nhtsa.dot.gov/Cars/rules/rulings/TirePresFinal/FEA/TPMS3.html Braking distance decreases as tire pressure increases. A larger contact patch does not give more traction as proven by the above study.
[edit] Load rating
Tires 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. For a table of load ratings, see tire codes.
Replacing a tire on a vehicle with one with a lower load rating than originally specified by the vehicle manufacturer will often render the insurance invalid.
[edit] Speed rating
The speed rating denotes the maximum speed at which a tire is designed to be operated. For passenger vehicles these ratings range from 99 mph (160 km/h) to 186 mph (300 km/h). For a table of speed ratings, see tire code.
Replacing a tire on a vehicle with one with a lower speed rating than originally specified by the vehicle manufacturer will often render the insurance invalid.
[edit] Service rating
Tires (especially in the USA) are often given service ratings. Mainly used on bus and truck tires. Some ratings are for long-haul and some for stop-start multi-drop type work. Tires designed to run 500+ miles per day carrying heavy loads require special specifications.
[edit] Rotation
Tires may exhibit irregular wear patterns once installed on a vehicle and partially worn. Furthermore, front-wheel drive vehicles will wear the front tires at a greater rate compared to the rears. Tire rotation is the procedure of moving tires to different car positions, such as front-to-rear, in order to even out the wear, thereby extending the life of the tire. It should be noted that with radial tires, once used, the direction of rotation should not be changed (except for emergency use).
[edit] Wheel alignment
When mounted on the vehicle, the wheel and tire may not be perfectly aligned to the direction of travel, and therefore may exhibit irregular wear. If the discrepancy in alignment is large, then the irregular wear will become quite substantial if left uncorrected.
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.
[edit] Retread
Tires that are fully worn can be re-manufactured to replace the worn tread. This is known as retreading or recapping, a process of buffing away the worn tread and applying a new tread.[5] Retreading is economical for truck tires because the cost of replacing the tread is less than the price of a new tire. Retreading passenger tires is less economical because the cost of retreading is high compared to the price of a new tire. However, commercial truck drivers run the risk of "blow-outs", separation, and tread peeling from the casing, due to re-use of the tire casing. To reduce these problems, tire technicians and the retread plant must ensure the casing is in the best condition possible. Tires casings that have problems such as capped tread, cannot be separated, have corroded belts, sidewall damage, or any run-flat or skidded tires will be rejected.
In most situations, retread tires can be driven under the same conditions and at the same speeds as new tires with no loss in safety or comfort.[6] The percentage of retread failures should be about the same as for new tire failures, but many drivers, including truckers, are guilty of not maintaining proper air pressure on a regular basis and if a tire is abused (overloaded, underinflated, or mismatched to the other tire on a set of duals), then that tire (new or recapped) will fail.[7]
Many commercial trucking companies put retreads only on trailers, and use new tires on their steer and drive wheels.[citation needed] This ensures that in the event of problems with a retreaded tire, the driver maintains control over the truck.
[edit] Flat
A flat tire occurs when a tire deflates to the point where the metal of the wheel rim comes to ground level. This can occur as a result of normal wear-and-tear, a leak, or more serious damage. A tire which has lost sufficient pressure to cause it to become distorted at the bottom will impair the stability of the vehicle and may further damage the tire if it is driven in this condition. The tire should be changed and or repaired before it becomes completely flat. Continuing to drive a vehicle with an absolutely flat tire will likely result in damaging the tire beyond repair, possible damage to the rim and vehicle, and will put the occupants, and other vehicles in danger. A flat tire or low pressure tire should be considered an emergency situation, requiring immediate attention to rectify the problem.
[edit] Hydroplaning (or aquaplaning)
Hydroplaning, also known as aquaplaning, is the condition where a layer of water builds up between the tire and road surface. Hydroplaning occurs when the tread pattern cannot channel away enough water at an adequate rate to ensure a dry footprint area. When hydroplaning occurs, the tire effectively "floats" above the road surface on a cushion of water - and loses traction, braking and steering, creating a very unsafe driving condition. When hydroplaning occurs, there is considerably less responsiveness of the steering wheel. The correction of this unsafe condition is to gradually reduce speed, by merely lifting off the accelerator/gas pedal.
Hydroplaning becomes more prevalent with wider tires.
[edit] Markings
[edit] DOT Code
In the United States, the DOT Code is an alphanumeric character sequence molded into the sidewall of the tire for purposes of tire identification. The DOT Code is mandated by the US Department of Transportation. The DOT Code is useful in identifying tires in a product recall.
The DOT Code begins with the letters "DOT" followed by a plant code (two numbers or letters) that identifies where it was manufactured. The last four numbers represent the week and year the tire was built. A three-digit code was used for tires manufactured before the year 2000. For example, 178 means it was manufactured in the 17th week of 8th year of the decade. In this case it means 1988. For tires manufactured in the 1990s, the same code holds true, but there is a little triangle (Δ) after the DOT code. Thus, a tire manufactured in the 17th week of 1998 would have the code 178Δ. After 2000, the code was switched to a 4-digit code. Same rules apply, so for example, 3003 means the tire was manufactured in the 30th week of 2003.
Other numbers are marketing codes used at the manufacturer's discretion.
[edit] E-mark
All tires sold for road use in Europe after July 1997 must carry an E-mark. The mark itself is either an upper case "E" or lower case "e" - followed by a number in a circle or rectangle, followed by a further number. An (upper case) "E" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. A (lower case) "e" indicates that the tire 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 tire size and type.
[edit] Mold serial number
Tire manufacturers usually embed a mold serial number into the sidewall area of the mold, so that the tire, once molded, can be traced back to the mold of original manufacture.
[edit] Codes
[edit] Use classifications
Tires 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 tire type, it is common for tire factories to specialize in one or more tire types. In most markets, factories that manufacture passenger and light truck radial tires are separate and distinct from those that make aircraft or OTR tires.[citation needed]
[edit] Passenger and light truck types
[edit] High performance
High performance tires are designed for use at higher speeds, and more often, a more "sporty" driving style. They feature a softer rubber compound for improved traction, especially on high speed cornering. The trade off of this softer rubber is shorter tread life.
High performance street tires sometimes sacrifice wet weather handling by having shallower water channels to provide more actual rubber tread surface area for dry weather performance.[citation needed] The ability to provide a high level of performance on both wet and dry pavement varies widely among manufacturers, and even among tire models of the same manufacturer. This is an area of active research and development, as well as marketing.
[edit] Mud and Snow
Mud and Snow, (or M+S, or M&S), is a classification for specific winter tires designed to provide improved performance under low temperature conditions, compared to all-season tires. The tread compound is usually softer than that used in tires for summer conditions, thus providing better grip on ice and snow, but wears more quickly at higher temperatures. Tires may have well above average numbers of sipes in the tread pattern to grip the ice.
Dedicated winter tires will bear the "Mountain/Snowflake Pictograph" if designated as a winter/snow tire by the American Society for Testing & Materials. Winter tires will typically also carry the designation MS, M&S, or the words MUD AND SNOW (but see All-season tires, below).
Some winter tires may be designed to accept the installation of metal studs for additional traction on icy roads. The studs also roughen the ice, thus providing better friction between the ice and the soft rubber in winter tires. 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 tires are used in the upper tier classes of ice racing[8] and rallying.
Other winter tires 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 tires, or traction aids (e.g. tire chains) on vehicles driven in certain areas during extreme conditions.
Mud tires are specialty tires 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 tires also tend to be wider than other tires, to spread the weight of the vehicle over a greater area to prevent the vehicle from sinking too deeply into the mud. However in reasonable amounts of mud and snow, tires should be thinner. Due to them having a thinner wheel base, the tire will have more pressure per square inch on the road surface, thus giving them greater traction. This does not compensate when the snow is too deep and the car can not reach the hard snow beneath or move in the first place. In these circumstances a larger robust vehicle would be more adequate to get out of the snow drift or mud patch because they are heavier to compact the snow to get grip.[citation needed]
[edit] All Season
The All Season tire 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 tire is a compromise, and is neither an excellent summer tire nor an excellent winter tire. 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 tires are also marked for mud and snow the same as winter tires, but never with a snowflake. Owing to the compromise with performance during summer, winter performance is usually poorer than a winter tire.
[edit] All-terrain
All-terrain tires are typically used on SUVs and light trucks. These tires often have stiffer sidewalls for greater resistance against puncture when traveling off-road, the tread pattern offers wider spacing than all-season tires to remove mud from the tread. Many tires in the all-terrain category are designed primarily for on-road use, particularly all-terrain tires that are originally sold with the vehicle.
[edit] Spare
Some vehicles carry a spare tire, already mounted on a wheel, to be used in the event of flat tire or blowout. Minispare, or "space-saver spare" tires are smaller than normal tires to save on trunk/boot space, gas mileage, weight and cost. Minispares have a short life expectancy, and low speed rating.
[edit] Run-flat
Several innovative designs have been introduced that permit tires to run safely with no air for a limited range at a limited speed. These tires feature still load supporting sidewalls and often plastic load-bearing inserts.
[edit] Heavy duty truck
Heavy duty tires are also referred to as Truck/Bus tires. These are the tire sizes used on vehicles such as commercial freight trucks, dump trucks, and passenger buses. Truck tires 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 tire performance.
[edit] Off-the-road (OTR)
The OTR tire classification includes tires for construction vehicles such as wheel loaders, backhoes, graders, trenchers, and the like; as well as large mining trucks. OTR tires can be of either bias or radial construction although the industry is trending toward increasing use of radial. Bias OTR tires are built with a large number of reinforcing plies to withstand severe service conditions and high loads.
Dramatically increasing commodity prices has led to shortages of new tires. As a consequence, multi-million dollar trucks can be idled for lack of tires, costing mines millions of dollars in lost productivity. This has led to a stronger effort to recycle old OTR tires. As of 2008, a new OTR tire can cost up to $50,000; retread tires are sold at half the price of new tires, and last 80% as long.[9] Retreading an OTR tire is labor intensive. First, the retreading technician must place the old tire in a buffing machine to remove what remains of the old tread; "skiving" allows this, which is the removal, by hand, of material the buffing misses. Next, the technician must inspect the tire, repairing defects. Lastly, the technician fills holes in the tire with rubber, applies a cement gum adhesive, and places the tire on a machine which will apply a new tread.[10]
[edit] Agricultural
The agricultural tire classification includes tires used on farm vehicles, typically tractors and specialty vehicles like harvesters. High flotation tires are used in swampy environments and feature large footprints at low inflation pressures.
[edit] Racing
Racing tires are highly specialized according to vehicle and race track conditions. This classification includes tires for top fuel dragsters, drift racers, Xtreme off road racing, oval track racers, jet-powered trucks, and monster trucks - as well as the large-market race tires for Formula One, NASCAR, rallying, MotoGP and the likes. Tires are specially engineered for specific race tracks according to surface conditions, cornering loads, and track temperature. Tires have also been specially engineered for drifting. Racing tires are often engineered to minimum weight targets, so tires for a 500 mile race may run only 100 miles before a tire change. Some tire makers invest heavily in race tire development as part of the company's marketing strategy and a means of advertising to attract customers with the same likes.
Racing tires are often not legal to use on normal highway usage.
[edit] Industrial
The Industrial tire classification is a bit of a catch-all category and includes pneumatic and non-pneumatic tires for specialty industrial and construction equipment such as skid loaders and fork lift trucks.
[edit] Bicycle
This classification includes all forms of bicycle tires, including road racing tires, mountain bike tires, and snow tires.
[edit] Aircraft
Aircraft tires are designed to withstand extremely heavy loads for short durations. The number of tires required for aircraft increases with the weight of the plane (because the weight of the airplane is distributed better). Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking effect. Aircraft tires are usually inflated with nitrogen or helium in order to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases, but common compressed air sources may contain moisture, which increases the expansion rate with temperature. Aircraft tires generally operate at high pressures, up to 200 psi (13.8 bar) for airliners, and even higher for business jets. Tests of airline aircraft tires have shown that they are able to sustain pressures of maximum 800 psi (55.2 bar) before bursting. During the test the tire had to be filled with water, instead of helium or nitrogen which is the common content of aircraft tires, to prevent the test room being blown apart by the pressure when the tire was burst.
Aircraft tires also include heat fuses, designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during a rejected takeoff or an emergency landing. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment.
The main purpose of requiring that an inert gas, such as nitrogen, be used instead of air, for inflation of tires on certain transport category airplanes is prompted by at least three cases in which the oxygen in air-filled tires combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature. The use of an inert gas for tire inflation will eliminate the possibility of a tire explosion.[11]
[edit] Motorcycle
There are many different types of motorcycle tires:
| | The factual accuracy of this section is disputed. Please see the relevant discussion on the talk page.(April 2008) |
Sport Touring - these tires are generally not used for high cornering loads, but for long straights, good for riding across the country.
Sport Street - these tires are for aggressive street riders that spend most of their time carving corners on public roadways. These tires do not have a long life, but in turn have very good traction in high speed cornering.
Track or Slick - these tires 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 tires 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 tire, there will be less contact patch in the center, causing the tire to develop a flat spot quicker when used to ride on straightaways for long periods of time and have no tread so they lose almost all grip in the wet.