Off the road tires – my explaination
What is a tire? A tire or tyre is a ring-shaped vehicle component that covers the wheel rim to protect it and enable better vehicle performance. Most tires, such as those for automobiles, trucks, all types of working equipment, provide traction between the vehicle and the road while providing a flexible cushion that absorbs shock. So "no", they are not just made from black rubber. Tires and wheels is my main focus, so I spend my days dealing with a wide range of customer inquiries about these products. In most cases, it all starts with knowing the tire size to answer a customer’s question or to solve the tires and rims issue.
OTR (Off-the-Road) tires vary in size and chemical composition depending on the type of tire necessary for a particular job or job site environment. Since my job focus is off-the-road I will mostly limit my discussion to heavy equipment that operates off the road. There are however many other applications that require wheels that are made from non-rubber materials such as polyurethane mold on designs. A tire manufacturer designs their product around the sizes, types and dimensions of products produced by wheel rim manufacturers are currently making. However, there are special applications custom wheels and rim and tire packages need to be created based on an equipment manufacturers unique performance and design requirements.
For now, sticking with rubber tire products, the design and manufacturing of OTR tires by the tire company is an exact science in creating a rugged rubber compound that can take a beating on the job site, i.e. moving huge loads of earth in construction and mining. OTR tire companies employ engineering teams to develop the specialized chemical compounds for their OTR tires. Off road tires and off road wheels fitted for off road vehicles come in many tire sizes. Construction machinery, earthmoving equipment, agricultural machinery and mining equipment all take wheels and tires made in varying sizes, tire diameter, tread patterns, load carrying capacities and tire speed ratings. Off road wheels and tires are an important consideration to any company building machines in the heavy equipment industry. During the machine design process engineers take into consideration the machine performance requirements and come up with a package of wheel and tire packages they consider ideal to make a machine perform most efficiently. Simply put, rims and tires are essential.
The tire manufacturing process takes all the materials that compose a modern pneumatic tire such as synthetic rubber, natural rubber, fabric and wire, along with carbon black and other chemical compounds, and combines them into amazingly high tech tire designs. All tires consist of a tread and a body. The tread provides traction while the body typically provides containment for a quantity of compressed air. Before rubber was developed, the first versions of tires were simply bands of metal that fitted around wooden wheels to prevent wear and tear. Early rubber tires were solid (not pneumatic). Today, the majority of tires are pneumatic inflatable structures, comprising a doughnut-shaped body of cords and wires encased in rubber and generally filled with compressed air to form an inflatable cushion. Pneumatic tires are used on many types of vehicles, including cars, bicycles, motorcycles, buses, trucks, heavy equipment, and aircraft.
The indispensable team - the tire, the air pressure and the wheel.
There are two aspects to how pneumatic tires support the rim of the wheel on which they are mounted. First, tension in the cords pull on the bead uniformly around the wheel, except where it is reduced above the contact patch. Second, the bead transfers that net force to the rim.
Air pressure, via the ply cords, exerts tensile force on the entire bead surrounding the wheel rim on which the tire is mounted, pulling outward in a 360-degree pattern. Thus, the bead must have high tensile strength. With no force applied to the outer tread, the bead is pulled equally in all directions, thus no additional net force is applied to the tire bead and wheel rim. However, when the tread is pushed inward on one side, this releases some pressure on the corresponding sidewall ply pulling on the bead. Yet the sidewall ply on the other side continues to pull the bead in the opposite direction. Thus, the still fully tensioned sidewall ply pulls the tire bead and wheel rim in the direction opposite to the tread displacement and matching the total force applied to push the tread inward. New tires are designed to operate at a range of recommended tire pressure readings. Maintaining proper air pressure is essential to optimal tire performance.
Pneumatic tires are manufactured in more than 450 tire factories around the world. Over one billion tires are manufactured in the tire manufacturing industry annually, making the tire industry a major consumer of natural rubber. Tire production starts with bulk raw materials such as rubber, carbon black, and chemicals and produces numerous specialized components that are assembled and cured. Many kinds of rubber compositions are used. The following information describes the components assembled to make a tire, the various materials used, the manufacturing processes and machinery, and the overall business model.
A tire carcass is composed of several parts: the tread, bead, sidewall, shoulder, and ply.
Image By MagentaGreen (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Tread. The tread is the part of the tire that comes in contact with the road surface. The portion that is in contact with the road at a given instant in time is the contact patch. 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 tire 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 and evacuate water. Tread patterns feature non-symmetrical (or non-uniform) lug sizes circumferentially to minimize noise levels at discrete frequencies. 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.
Tire 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.
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. These forces are described as Force Variation.
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.
The bead is the part of the tire that contacts the rim on the wheel. The bead is typically 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 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 is a factor in the handling characteristics of an automobile, truck or type of equipment, because the rim supports the tire's profile.
The tire sidewall is that part of the tire that bridges between the tread and bead. The sidewall is largely rubber but reinforced with fabric or steel cords that provide for tensile strength and flexibility. The sidewall contains air pressure and transmits the torque applied by the drive axle to the tread to create traction but supports little of the weight of the vehicle, as is clear from the total collapse of the tire when punctured. Sidewalls are molded with manufacturer-specific detail, government mandated warning labels, and other consumer information, and sometimes decorative ornamentation, like whitewalls.
The shoulder is that part of the tire at the edge of the tread as it makes transition to the sidewall.
Tires are mounted onto wheels that most often have integral rims on their outer edges to hold the tire. Automotive wheels are typically made from pressed and welded steel, or a composite of lightweight metal alloys, such as aluminum or magnesium. These alloy wheels may be either cast or forged. The mounted tire and wheel assembly is then bolted to the vehicle's hub.
Steel wheels for heavy equipment, earth moving equipment and a variety of construction machines are made from thick sheets of steel plate or from hot formed steel sections produced at steel mills. The steel used is made of special formulations made to give the steel enhanced performance characteristics for use in wheels. Off the road wheels are manufactured in many design profiles, thickness and different manufactures are known to provide special designs promoting niche specific enhancements that also promote their unique brands. Off road rims come in a range of standard sizes and rim profiles. There are also several custom wheels and tires out in the market place as well. Those are usually niche products designed for special use cases.
The beads of the tire are held on the rim, or the "outer edge" of a wheel. These outer edges are shaped to obtain a proper shape on each side, having a radially cylindrical inclined inner wall on which the tire can be mounted. The wheel's rim must be of the proper design and type to hold the bead of the appropriately sized tire. Tires are mounted on the wheel by forcing its beads into the channel formed by the wheel's inner and outer rims.
What constitutes an OTR tire? Tires seem like very simple things, don’t they? Many people assume that a tire is just a basic round piece of rubber that is inflated by a tube. In the retail industry, there are thousands of different variants of tire depending on the manufacturer and the use that it will be put to. Off-the-road tires or, OTR tires, are built to take a massive amount of weight and roll through conditions that would stop most cars dead. They all share 3 common types of construction: bias, belted bias and radial.
Bias – A Bias tire means that it is of cross ply construction. It uses cords that stretch from bead to bead. A bead is a bunch of high tensile steel wire that ties the tire to the rim. The cords are laid in layers at opposing angles of approximately 35 degrees to form a crisscross pattern. The tread is then adhered over that pattern. The primary advantage of a tire with this construction is that it allows for the entire body of the tire to flex. This flexibility allows for a comfortable and smooth ride even on uneven or rough terrain. The down side of bias tires is that they have less traction and control at higher speeds.
Belted Bias – An OTR tire of this type starts out with similar construction to the bias. It will usually have two or more of the crisscross layers that we mentioned before but it then has corded or steel stabilizing belts that are attached underneath the tread. Those belts and crisscross layers are at differing angles similar to the Bias tire listed above. This construction really improves the tires performance when put up against non-belted bias tires. Belted Bias is an improvement on the bias because it retains the comfortable ride but the increased stiffness of the construction lessens the rolling resistance at high speeds.
Radial – A radial tire is in some ways the opposite of a bias tire and in others it is combination of Bias and Belted Bias. Radial utilizes cords that extend from the beads and across the tread but they are at right angles to the centerline of the tread. The cords are parallel to one another and stabilizer belts are put into place beneath the tread. All those things come together to strengthen the tire and provide a longer life for the tire, better control at high speeds and lower rolling resistance as well. The disadvantages are that the ride is much rougher at lower speeds and OTR tires will not see as much of a self-cleaning ability.
Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plastic compounds via molding operations. Solid tires include those used for lawn mowers, skateboards, golf carts, scooters, and many types of light industrial vehicles, carts, and trailers. One of the most common applications for solid tires is for material handling equipment (forklifts). Such tires are installed by means of a hydraulic tire press.
Semi-pneumatic tires have a hollow center, but they are not pressurized. They are light-weight, low-cost, puncture proof, and provide cushioning. These tires often come as a complete assembly with the wheel and even integral ball bearings. They are used on lawn mowers, wheelchairs, and wheelbarrows. They can also be rugged, typically used in industrial applications, and are designed to not pull off their rim under use.
Tires that are hollow but are not pressurized have also been designed for automotive use, such as the Tweel (a portmanteau of tire and wheel), which is an experimental tire design being developed at Michelin. The outer casing is rubber as in ordinary radial tires, but the interior has special compressible polyurethane springs to contribute to a comfortable ride. Besides the impossibility of going flat, the tires are intended to combine the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to cornering forces offered by low profile tires. They have not yet been delivered for broad market use
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. Tires should not generally be inflated to the pressure on the sidewall; this is the maximum pressure, rather than the recommended pressure
Inflated tires naturally lose pressure over time. Not all tire-to-rim seals, valve-stem-to-rim seals, and valve seals themselves are perfect. Furthermore, tires are not completely impermeable to air, and so lose pressure over time naturally due to diffusion of molecules through the rubber.
The tire contact patch is readily changed by both over-and-under inflation. Over-inflation may increase the wear on the center contact patch, and under-inflation will cause a concave tread, resulting in less center contact, though the overall contact patch will still be larger. Most modern tires will wear evenly at high tire pressures, but will degrade prematurely if underinflated. An increased tire pressure may decrease rolling resistance, and may also result in shorter stopping distances If tire pressure is too low, the tire contact patch is greatly increased. This increases rolling resistance, tire flexing, and friction between the road and tire. Under-inflation can lead to tire overheating, premature tread wear, and tread separation in severe cases.
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 code.
The tire speed rating denotes the maximum speed at which a tire is designed to be operated. For passenger vehicles, these ratings range from 160 to 300 km/h (99.4 to 186 mph). For a table of speed ratings, see tire code.
Tires (especially in the U.S.) 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 (800 km) or more per day carrying heavy loads require special specifications.
The treadwear rating or treadwear grade is how long the tire manufacturers expect the tire to last.
Rolling resistance is the resistance to rolling caused by deformation of the tire in contact with the road surface. As the tire 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 tire structure, such as spring force and stiffness. Tire makers seek lower rolling resistance tire constructions to improve fuel economy in cars and especially trucks, where rolling resistance accounts for a high proportion of fuel consumption.
Pneumatic tires also have a much lower rolling resistance than solid tires. Because the internal air pressure acts in all directions, a pneumatic tire can "absorb" bumps in the road as it rolls over them without experiencing a reaction force opposite to the direction of travel, as is the case with a solid (or foam-filled) tire.
Tires for Off-The-Road applications, such as mining, earthmoving and port applications, are required to be specialized and tough and mounted on steel rims. OTR tires are offered in a wide range of designs in both Radial and Diagonal constructions and are popular with machine manufacturers, mining companies and ports. The off the road product portfolio includes tires for the entire spectrum of OTR machines like loaders, graders, bulldozers, rigid dump trucks, articulated dump trucks, straddle carriers, empty container handlers and reach stackers, agricultural equipment, ATV, RTV, UTV machines, earthmover equipment, backhoes, industrial equipment, Lawn, garden, and turf machines, material handlers, military type vehicles, off-road flotation type machines, construction, mining, skid steer, rough terrain telehandlers, Man lifts, telehandler and telescopic lifts. Most importantly off the road tires are engineered to last long and provide efficient service.
OTR tires are manufactured for the world’s largest construction vehicles such as haul trucks, wheel loaders, backhoes, graders, rough terrain forklift, and trenchers. OTR tires are designed as either bias or radial construction. The OTR tire industry is increasing the use of radial tire designs due to the improved performance of radial tire designs. Companies dependent upon OTR tires should walk away from tire products not covered by a warranty that promises a quick response to any malfunction pertaining to their products.
Joedamadman at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
OTR Tires and heavy duty tires are classified by the type of vehicles they are used on. For example
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, heavy duty tire 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.
Rubber 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 motor scraper, 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.
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.
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.
Tire Specification Code. It is most critical that Off-the-Road tires are properly matched to the job, oem wheels, 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.
OTR tire designers utilize state-of-the-art testing, destructive and non destructive testing, to make sure the inner workings of the tire will hold up when pushed to their limits, but also focus on a tread specific to what the customer requires. This testing is vital when a company’s reputation is on the line. For example, there is a rigorous testing process that judges the heat created by OTR tires when in use which gauges exactly how heat is spread throughout the interior of the rubber. This test is important to discover how much pressure the tire can endure. Tire engineers use techniques such as computer modeling, ndt testing, x-ray inspection, and strenuous road testing to ensure OTR tire designs provide the performance required to conquer every environmental condition. Tire construction may appear to be a simple process but it far from that.
OTR tires keep heavy mining and construction equipment moving forward under dangerous conditions coupled with the pressure of meeting mining and construction production timelines. The thorough computer modeling and testing conducted by tire engineering teams improve the life span of OTR tires by developing better tire designs. Better designs mean less downtime from tire failures and cost savings to the customer.
These categories only represent the basic construction of OTR tires. There are many more OTR tire varieties available that are designed for special environments and conditions. Such as tires for equipment used in:
Agricultural, ATV, RTV, UTV’s, road graders, heavy equipment, earthmover, backhoes, industrial equipment of all sorts, lawn, garden, and turf equipment, wheel loader, material handling, military type equipment, off-the-road earthmoving, construction and mining equipment, skid steers, rough terrain telehandlers, man lifts, and telehandlers.
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