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TYRES
TYRES
Pneumatic automobile tyre
Tires, or tyres (in American and British English, respectively), are ring-shaped parts, either pneumatic or solid (including rubber, metals and plastic composites), that fit around wheels to protect them and enhance their function.
Pneumatic tyres are used on many types of vehicles, such as bicycles, motorcycles, cars, trucks, earthmovers, and aircraft.
History
The first practical pneumatic tyre was made by the Scot, John Boyd Dunlop, in 1887 for his son's bicycle, in an effort to prevent the headaches his son had while riding on rough roads (Dunlop's patent was later declared invalid because of prior art by fellow Scot Robert William Thomson).
Pneumatic tires are made of a flexible elastomer material, such as rubber, with reinforcing materials such as fabric and wire. Tyre companies were first started in the early 20th century, and grew in tandem with the auto industry. Today, over 1 billion tyres are produced annually, in over 400 tyre factories, with the three top tyre makers commanding a 60% global market share.
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Tread
The tread is the part of the tyre 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 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 (or non-uniform) lug sizes circumferentially in order to minimize noise. Sipes are valleys cut across the tire, usually perpendicular to the grooves, which allow the water from the grooves to escape to the sides in an effort to prevent hydroplaning.
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. Mud and snow (M&S) tires are designed with higher void ratios to channel away rain and mud, while providing better gripping performance.
Treadwear
The treadwear grade describes how long the tyre manufacturers expects the tyre to last. A Course Monitoring Tyre (the standard tire that a test tyre will be compared to) has a rating of "100". If a manufacturer assigns a treadwear rating of 200 to a new tyre, they are indicating that they expect the new tire to have a useful lifespan that is 200% of the life of a Course Monitoring Tyre.
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.
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 tire. Some tyre manufacturers claim that their tread pattern is designed to actively pump water out from under the tire by the action of the tread flexing. This results in a smoother ride in different types of weather.
Wear bar
Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tyre has reached its wear limit. 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.
Bead
The bead is that part of the tyre which contacts the rim on the wheel. The bead is reinforced with steel wire, and compounded of high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tyre 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 tyre is a factor in the handling characteristics of an automobile, because the rim supports the tire's profile.
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. 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 has recommended that tires be replaced when they are 6 years old to prevent sudden failure, even if the tyre looks undamaged.
Shoulder
The shoulder is that part of the tire at the edge of the tread as it makes transition to the sidewall.
Inflation pressure
Tyres 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 tyres 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. Tyres should not be inflated to the pressure on the sidewall; this is the maximum pressure, rather than the recommended pressure
If tyre pressure is too high, the tire contact patch is reduced, which decreases rolling resistance. However, ride comfort is reduced, but traction is not always reduced, stopping distance is not always increased. Also, going above max sidewall pressure rarely results in the center of the tyre wearing more than the shoulder
If tyre pressure is too low, the tyre contact patch is increased, increasing rolling resistance, tyre flexing and friction between the road and tyre. This "underinflation" can lead to tyre overheating, premature tread wear, and tread separation in severe cases. Braking distance did not statistically change as tire pressure increased, suggesting that a larger contact patch from underinflation may not be a significant contributor for the conditions explored in these specific tests.
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.
Replacing a tyre on a vehicle with one with a lower load rating than originally specified by the vehicle manufacturer will often render the insurance invalid.
Speed rating
The speed rating denotes the maximum speed at which a tyre is designed to be operated. For passenger vehicles these ratings range from 99 mph (160 km/h) to 186 mph (300 km/h).
Replacing a tyre on a vehicle with one with a lower speed rating than originally specified by the vehicle manufacturer will often render the insurance invalid.
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.
Retread/Remould
TYres 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. Retreading is economical for truck tyres because the cost of replacing the tread is less than the price of a new tyre. Retreading passenger tyres is less economical because the cost of retreading is high compared to the price of a new tyre. However, commercial truck drivers run the risk of "blow-outs", separation, and tread peeling from the casing, due to re-use of the tyre casing. To reduce these problems, tyre technicians and the retread plant must ensure the casing is in the best condition possible. Tyres or casings with problems such as capped tread, tread separation, corroded belts or 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. 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.
Markings
DOT Code
In the United States, the DOT Code is an alphanumeric character sequence molded into the sidewall of the tyre for purposes of tire identification. The DOT Code is mandated by the US Department of Transportation. The DOT Code is useful in identifying tyres 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 tyre 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 tyres manufactured in the 1990s, the same code holds true, but there is a little triangle (ÃŽâ€) after the DOT code. Thus, a tyre manufactured in the 17th week of 1998 would have the code 178ÃŽâ€. 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.
E-mark
All tyres 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 tyre is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. A (lower case) "e" 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.
Passenger and light truck types
Mud and Snow
Mud and Snow, (or M+S, or M&S), is a classification for specific winter tyres designed to provide improved performance under low temperature conditions, compared to all-season tyres. 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 tires 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 tires, below).
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, thus 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 tires are used in the upper tier classes of ice racing[11] 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 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 tires 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. However in reasonable amounts of mud and snow, tyres should be thinner. Due to them having a thinner wheel base, the tyre will have more pressure per square inch on the road surface, thus allowing the tires to penetrate the snow layer and grip harder snow or road surface beneath. This does not compensate when the snow is too deep for such penetration.
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 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 rarely with a snowflake. 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 tires that are originally sold with the vehicle.
been introduced that permit tires to run safely with no air for a limited range at a limited speed. These tires typically feature strong, load-supporting sidewalls. An infamous example of an alternate run flat technology has plastic load-bearing inserts attached to the rim instead of the reinforced sidewalls.
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