Tire Construction
BASIC COMPONENTS
The construction of Off-the-Road tires depends, to a large extent, on the intended use of the tire. However, there are common components, to all Off-the-Road tires, including the tread, carcass, beads, breakers and sidewalls. Tubeless-type tires have an inner liner.
TREAD
The tread is the outermost covering of the tire, and is the only part that normally comes in contact with the road surface. It, therefore, must be designed to protect the body of the tire from cuts and wear. Depending on the intended use of the tire, the rubber compound applied to the tread will be changed to customize cut resistance, heat resistance and oil resistance. The tread pattern also has a large effect on the performance of the tire.
CARCASS
The compressed air in a tire supports the load placed on the tire. The carcass forms a semi-rigid frame for the compressed air, but is flexible enough to absorb some shocks and jolts. The carcass of Bias tires consists of a number of rubber-coated layers of fabric called "plies."
BEAD
The bead fixes the tire to the rim to support the load.
BREAKER
The breaker of a Bias tire is rubber-coated layers of cord between the tread and carcass, binding the two together. The breaker prevents cuts in the tread from reaching the carcass and helps absorb shocks.
SIDEWALL
The sidewall is composed of a flexible, crack-resistant rubber, and protects the carcass from damage. For jobs where chuckholes, large rocks, etc. are a problem, tires with high cut-resistant sidewalls can be used.
INNER LINER
The inner walls of tubeless tires are lined. The liner is made of an air-impermeable rubber compound and is comparable to tubes in tube-type tires. Tubeless tires generally weigh less than comparable tube-type tires and are simpler to maintain because the tube and flap are eliminated.
STEEL BREAKER
The steel breaker tire has steel cord breakers that give it very high cut resistance. It is especially useful where sharp rock is a problem, and is applicable to loader, dozer, dump truck and occasionally earthmover type tires. The adhesiveness between the steel cord and rubber, however, is more susceptible to heat damage than that of nylon cord and rubber. Accordingly, steel breaker tires should not be subjected to conditions where heat generation is great. Because of the difficulty involved in retreading steel breaker tires, they should not be used for jobs where more easily retreaded tires can be used. Steel breakers that extend to the sidewall are also available for jobs where high sidewall cut resistance is required.
RADIAL TIRES
The radial tire has two carcass components, both consist of steel. The first is a single bead to bead carcass ploy which carries the load and supports the tread. The carcass ply runs at a 90 degree angle in relation to the tire bead. The second is low angle steel belts which are placed on the top of the carcass ply and under tread rubber to minimize tread distortion.
TIRES BY TYPE OF VEHICLE
DUMP TRUCKS
(TRA Codes E-1, E-2, E-3 and E-4)
Since dump trucks must travel under heavy load at high speeds, over relatively long distances, tires for dump trucks must have high heat and wear resistance. Sometimes high resistance to cuts is also necessary.
SCRAPERS
(TRA Codes E-2, E-3 and E-4)
Scraper tires, of which the wide base type is the most common, should have the same properties as those for dump trucks. Superior flotation and traction are also occasionally required.
FRONT-END LOADERS
(TRA Codes L-2, L-3, L-4, L-5, L-4S and L-5S)
Since front-end loaders operate on rough ground, cut and wear resistance are vital and the tires must provide stability for the loader body. Flotation and traction properties may also be necessary, depending on the working conditions. In certain cases, such as the wet and rough conditions of underground mines, the L-4S and L-5S with smooth treads are used because of their high wear and cut resistant properties.
TIRE DOZERS
(TRA Codes L-2, L-3, L-4 and L-5)
Since a tire dozer is used not only for dozing and leveling, but sometimes for pushing a motorscraper, tires with better traction than loader tires are necessary. Other requirements vary widely depending on job conditions.
MOTOR GRADERS
(TRA Codes G-2 and G-3)
The motor grader, which is used for road leveling, clearing and snow removal, needs tires that provide high traction and directional stability. Other characteristics depend on job requirements.
TIRE ROLLERS
(TRA Code C1)
Tire rollers use wide tread tires that uniformly distribute weight because of their primary use in compacting road surfaces.
STRADDLE CARRIERS
(Industrial Service)
Straddle carriers are special vehicles that are mainly used at seaport areas to carry ocean-going freight containers. These tires require extra heavy-duty performance, and wear and heat resistance, because straddle carriers operate continuously and turn frequently.
TOWING TRACTORS
(Industrial Service)
Towing tractors are used to move large aircraft. Thus, these tires mainly require extra traction.
TREAD DESIGN
The tread pattern is designed to produce varying degrees of traction, cut, flotation, wear and heat resistance. So selection of the proper Off-the-Road tire depends on the job and the conditions. For example, different tread patterns are used to produce maximum traction or flotation on sand, mud and rock. There are five basic tread patterns: rock, traction, block, rib and smooth.
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ROCK PATTERN
The rock pattern is specially designed to prevent cuts caused by sharp rock. Its large ground contact area provides maximum contact area provides excellent wear resistance. Characteristic grooves running across the direction of the travel mark the most popular tread pattern for Off-the-Road tires.
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TRACTION PATTERN
The traction pattern tire has a directional tread design, which means the direction of mounting on the rim is important. For example, the mounting direction should place the tread facing one way on the drive wheels to produce proper traction, while on the free rolling wheels, the tread should face the opposite direction.
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BLOCK PATTERN
The block pattern tire is mostly characterized by wide tread width and rounded shoulders. Under heavy loads, the block pattern's large ground contact area creates low ground contact pressure, for good flotation properties. Therefore, it is well suited for use on soft, muddy ground. This pattern is also called the "alligator" or "button" pattern.
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RIB PATTERN
The rib pattern tire has grooves running parallel to the direction of travel and gives high directional stability. The rib-lug pattern, a variation of the rib pattern, has lugs on the shoulders of the tread. Rib pattern tires are mainly used on free-rolling wheels.
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SMOOTH PATTERN
The smooth pattern tire, designed for tire rollers, has no grooves. It is used for compacting and leveling. A smooth pattern tire can also be used on loaders in underground mines because of its high wear and cut resistance. The smooth pattern for loaders, however, has two narrow grooves that are used to measure tread wear.
TREAD THICKNESS
According to the Tire and Rim Association, Incorporated (TRA), there are three general classifications of tread thickness for Off-the-Road tires: regular, deep and extra-deep. Deep and extra-deep are 1.5 and 2.5 times thicker than regular, respectively. The thicker treads have greater cut and wear resistance. The TRA codes are classified as follows:
Extra-Deep Tread: L-5, L-5S Deep Tread: E-4, L-4 and L-4S Regular Tread: E-2, E-3, G-2, G-3, L-2 and L-3
Although thicker treads give greater wear and cut resistance, they also generate and retain more heat. Accordingly, work conditions for tires with thick treads should be thoroughly evaluated to prevent heat separation and other heat-related damage. Deep and extra-deep tread tires have almost the same overall diameter, which is larger than regular tread tires. When replacing regular tread tires with deep or extra-deep tread tires, the larger overall diameters of the thicker tread tires should be taken into consideration.
SIZE IDENTIFICATION AND ASPECT RATIO
The size of an Off-the-Road tire is normally indicated by tire width, rim diameter and ply rating. The nomenclature for this is as follows:
| Tire Width (inches) | Rim Diameter (inches) | Ply Rating |
|---|---|---|
| 21.00 | 35 | 36PR (narrow base) |
| 26.5 | 25 | 20PR (wide base) |
A narrow base tire has an aspect ratio (tire height/tire width) of 96~98% and a wide base tire has an aspect ratio of 80~82%. Widths of narrow and wide base tires of the same diameter are shown below:
| 13.00-15.5 | 21.00-26.5 |
| 14.00-17.5 | 24.00-29.5 |
| 16.00-20.5 | 27.00-33.5 |
| 18.00-23.5 | 30.00-37.5 |
For example, the overall diameters of 18.00-23.5 E3 and 23.5-25 E3 are 63.5 inches and 63.8 inches: almost the same. According to TRA guidelines, tires with an aspect ratio of 65~70% are called super low profile tires and provide high flotation and stability and are usually indicated as follows: tire width/aspect ratio-rim diameter (40/65-39). Some low profile tires are also indicted by overall diameter x tire width-rim diameter (42 x 17-20). A suffix, NHS, TG or K may be attached. These are TRA designations used to differentiate between tires requiring certain conditions. NHS: Not for highway service, TG: Tractor-grader tires, not for highway use, and K: Compactor tire for use on 5 drop center or semi-drop center rims having bead sears with nominal minus 0.032 diameter.
TIRE SPECIFICATION CODE
It is most critical that Off-the-Road tires are properly matched to the job and road conditions anticipated. Accordingly, Off-the-Road tires are classified by three types: regular tire, cut-resistant tire and heat-resistant tire. The regular type provides general performance for use under standard conditions. Where many obstacles pose cut damage, cut protected types are most suitable. And under good road conditions where higher speeds can be attained, heat-resistant types are recommended. Yokohama follows the above classifications.