Co-authored by Mr. Len Hensel, BSME, MS-PDD Wheel Engineer and Keith Heeres
The tire indexing, tire slippage, or tire spinning on rim problem we are looking at is as it relates to off the road equipment used in earthmoving, construction, mining and other heavy equipment applications. Tires spinning on rims is commonly talked about in automotive, off road recreational vehicles, bikes and motorcycles. Same type problem occurs on the big machines as well but for similar and some different reasons. Tire indexing is the topical term we use in the off the road industry to discuss the problem with tires and wheels.
Many wheel loader operators have experienced situations when they are pulling out of an aggregate pile, the tires are moving but not going very fast. At this point, the operator then realizes that the tire is slipping or tire is spinning on the rim/wheel. The end result can be a chewed up tire bead area which is expensive to replace. Other issues can result that will impact the availability and productivity of the machine. For over the road type of applications, tire indexing can lead to air loss and ride disturbance complaints.
Tire indexing is a problem of all pneumatic tire assemblies that are used with any type over-the-road vehicles or off road equipment. Off road equipment with high engine power/torque is more prone to tire indexing. Typically this would be all sizes of wheel loaders, rubber tired wheel dozers, and container handlers just to name a few. Construction equipment has been noted as experiencing tire indexing but other off road applications such as agricultural, industrial and mining will experience tire indexing as well. Tire indexing has been observed with non-drive axle application such as quarry and large mining haul trucks. Tire Indexing can occur because of high braking forces/torques. A non-drive axle would typically be the front steer positions of a haul truck.
So, what is tire indexing? What causes it? How can this be limited or stopped? What can be done about it? In this article we will address some of these basic questions.
The definition that is used in this article is “the permanent circumferential rotation of one or more of the tire beads relative to the bead seat(s) of the rim”. Along with this, the tire is not slipping on the ground. The tire traction with the ground is able to transfer all the static and dynamic forces from the equipment.
Other terms are used in the off road applications. Some of the terms are:
· Rim slippage or tire slippage or tire slippage on rim
· Rim spinning or tire spinning or tire spinning on rim or wheel
These terms generally mean the same thing.
It is important to note that the wheel is typically bolted to the drive axle so it cannot slip relative to the machine hub. The movement we see is the tire slipping on the rim bead seats. For a person observing tire indexing from the side of the road, it appears that the tire is stationary and the rim/wheel is turning inside the tire. In this article, the tire is the component that is indexing relative to the equipment driveline.
Tire slippage occurs with agricultural tires used in tractor applications. The drive tires have some intended slippage (especially in all-wheel drive configurations) with this type of application while they are under drawbar torque. A certain amount of slip at the ground is needed for efficient operation of the tractor. This type of slip is not addressed in the article.
Tire indexing can occur with passenger tire and wheel assemblies as well. In this application the driveline and braking forces are causing the movement of the tire. The consequences of the tire indexing is ride disturbance (change of tire assembly balance, change in the radial runout) that the driver and passengers that feel inside the vehicle. This type of indexing is not the primary focus of this article. However, cause 1 & 2 discussed later in this article do apply to passage car application.
There is a style of rim mounting called “demountable”. In this design the rim is clamped to the hub of the driveline. With this type of mounting the rim can slip on the hub because of drive or braking torques. We are also not addressing this situation in this article.
Tire indexing is an axle end system issue. Important note: The word system is being used because we have individual components that must work together so the drive or braking torques is transferred through the equipment to the ground.
The basic system components (tires, wheels, hubs, brakes) must work together so the equipment can move or stop when needed. When one component of the system does not function properly, tire indexing can be one of the consequences. When you have a system issue, factors and characteristics influencing it can be a combination of characteristics and not just a single characteristic.
Before we discuss the causes and factors that contribute to off the road tire indexing, we need to review the basics of tires and wheels.
The diagram on the right shows a typical cross section of a radial tire.
When we make mention of “the bead”, “bead area”, “Lower tire bead area” we are referring to item #1.
· When referring to the tire bead seat area we are referring to item #13.
Tires used in off road applications have several types of construction configurations. While many people know what these are, we will review them here anyway.
Tires, regardless of the application, can be separated into two very broad groups, tube-type (TT) and tubeless (TL).
Tube-type tires are constructed with rubber and other materials such as steel, nylon, and polyester. Rubber is a porous material from an air migration standpoint. An example of this would be inflating a balloon until it is big and taught. If we let it stand for a few days it begins to shrink because the air inside is migrating through the rubber wall of the balloon. In the early days of the pneumatic tires a special compound was developed to prevent air migration from occurring. This became the material used for tubes. Tubes have been used in tires for over 125 years and are still used today in over-the-road and off road applications.
The tube is located on the inside of the tire and acts like a big balloon. A flap, which is also made of rubber, is placed between the bottom of the tube and the rim. The flap protects the tube from chaffing against the rim and provides support around the valve slot add area. The tube is inflated through a valve stem which is generally located at the bottom of the tube.
When tire indexing occurs, the tube will move along with the tire because of the frictional forces between the tire and the tube. The valve stem however will not move and at some point the valve will separate from the main tube and cause immediate loss of air.
The tubeless tire was first introduced around 1947. This marked a significant technology advancement to reduce the tire system complexity and improve the reliability of the tire and wheel assembly. The tubeless tire was introduced into the off road applications around 1955. TL tires eliminated one field issue with tire indexing - the shearing off the valve stem. While indexing can still occur, the valve stem is part of the rim now that when the tire moves; it does not affect the valve stem. More than 90% of the tires produced today are tubeless construction. However, tubes can still be installed in these tires for special situations.
The next broad grouping of tires we will discuss is the type of internal tire construction. Each of the construction types we will discuss below can be made as a tube type with tubeless features. But as noted above, the vast majority of tires are made for tubeless operation.
Tires were originally made with rubberized cotton fabric (ply) to provide strength to the tire to resist the air pressure and support the load on the tire. Several ply layers were used with each ply having a different angle relative to each other. This allowed for the proper strength in the tire to be achieved. The plies are wrapped around to the tire bead. With this type of construction 1, 2 or 3 bead bundles will be used depending on the number of actual plies used in the construction. Modern materials used for the fabric plies have allowed the actual number of plies to be reduced, but the strength of the tire has increased. Bias tires tend have a stiff construction and provide good lateral load resistance.
Lateral loads (or forces) are those that push or pull against the sidewall or lower bead area of the tire. Typically these forces are caused by:
- Dynamic forces from maneuvering corners or other turning events
- Travelling on the side of an incline
- Dynamic forces from high center of gravity operations such as material lifts
When multiple bead bundles are used, a wide tire bead aids in resisting tire indexing because of a larger surface area to transmit the torque. Bias tires have a unique pressure pattern in transferring loads and pressures in the rim. More pressure is applied to the bead seat surface as compared to the radial tire construction. This also aids in resisting indexing.
The radial tire construction was introduced to the market place in in the 1950’s. This construction provided many performance improvements compared to bias tires and has allowed performance capabilities to be expanded beyond the limitations of bias tire construction.
Tire durability, TKPH (Tonne kilometer per Hour) ratings and other characteristics improved dramatically. Changes in the manner in which forces are transmitted between the tire and the rim and the lower lateral stiffness characteristics tended to cause an increase in tire indexing.
The main function of the rim is to provide support to the tire and to facilitate the passing of forces from the driveline of the equipment to the tire. There are several construction styles of rims used in off the road applications:
There are standard and heavy duty designs in the market place. Standard or heavy duty designs as it relates to the thickness of the steel material used to form the rim and the overall profile design of the rim. Standard duty designs are typically used in various agricultural applications. The heavy duty designs are typically used in construction applications (motor graders, small front end loaders) and high load applications such as harvester and logging applications. All designs are intended to be used with tubeless tires. However, inner tubes can be used. The rim profile has 50 taper for the bead seat surface to create a tight fit with the tire bead area. Knurling is included with some rim sizes to address tire indexing. Because this is a single piece construction, there are no loose components that exhibit circumferential movement.
These rims are commonly referred to as “flat base” style. They are typically used with tube-type tires in rim diameters from 15” to 24”. Normally a tube and flap is used with the tire to inflate the tire. The fixed flange side of the rim allows for some interference fit with the tire bead. Typically, there is no tire bead interference fit with the removable side of the rim. There is a limited ability to resist tire indexing. There some tube type rim designs that can be converted to a three piece configuration that are used for heavy load applications. Some of the rim designs can be converted to use tubeless tires if an “L” style polymer sealing ring is used.
There is lightweight and heavy duty versions used in the marketplace with the same basic components. These designs are intended to be used with tubeless tires. An O-Ring groove has been added to the gutter band so that an O-Ring can be added to create a tubeless seal. The rim profile has 50 tapers for the bead seat surfaces to create a tight fit with the tire bead area. Knurling is an included feature for the heavy duty design to help in reducing tire indexing.
There are standard and heavy duty rim and wheel designs in the marketplace that use the same basic components. These designs are intended to be used with tubeless tires. An O-Ring groove is used in the gutter band so that an O-Ring can be used to create a tubeless seal. The rim profile has 50 tapers for the bead seat surfaces to create a tight fit with the tire bead area. Knurling is included to help reduce tire indexing. The side flanges are separate components included for design flexibility.
In several of the above rim styles, a feature called knurling has been mentioned. Knurling is a lateral serration feature that added to the bead seat surface to assist is resisting the tire bead from indexing. A good way to visualize the function of knurling is that it provides a means for the tire bead area to grab onto an otherwise smooth surface of the rim bead seats. Specifics of the knurling and when they are recommended to be used are specified by various recognized industry standards bodies such as the Tire & Rim Association (TRA).
With multi-piece rim and wheel designs, the loose components resist circumferential movement through frictional force resistance only. In many cases this is not sufficient to keep the components from rotating. Mechanical locking features are used with all high torque applications. Two basic locking systems used on off road rims and wheels are shown below.
This is the simplest version and was the first one used in the industry. Notches are cut in the bead seat band and gutter band. A lug or driver is attached to the lock ring. The lug fits into the notches so the bead seat band cannot rotate relative to the rim. Notching of the rim components has an impact on the strength of these rim assemblies. Normally when this style of driver pockets is used the operating inflation pressure is limited to a maximum of 65 PSI (4.5 bar) or less.
Note – This tends to be the standard industry practice in North America. In other global regions end users are running at higher pressure levels
There are several versions of this style used depending on the strength that is needed for the application. One driver pocket is welded to the side flange (or bead seat band). A second driver pocket is welded to the outboard surface of the gutter band. A driver key is then placed in between to lock the side flange/bead seat band from circumferential rotation.
With five piece style rims, the flanges are free to rotate with the tire. A driver lug is welded to the vertical portion of the flange and two lugs are welded to the rim back band or bead seat band. These lugs fit and work together to keep the flange from rotating with the tire. Thus adding more resistance to tire indexing or slippage.
Tire indexing involves the Output End of the driveline system. We are defining the output end as the tire, wheel and hub/axle. All of the driveline power, all of the braking forces and all dynamic forces must be supported and transmitted by each element of the tire and wheel system. Each element of the system must then work in concert with each other so that all the forces are efficiently transmitted to the ground. The function of the tire and wheel system is:
The tire and wheel assembly is a pressure vessel. The amount of load that it will support is based on the air volume of the tire and the air pressure necessary to carry that load. The load index (LI) or ply rating (PR) of the tire defines the load capacity it can support. Important note: The rim must be chosen to match the tire capacity/capability.
In operation shock loads must be supported because of rough road surfaces, undulations of the road surfaces, a tire running over road debris and sudden loads being dropped into an equipment body or bucket. In many applications the tires are the only suspension system for the equipment.
Primarily turning forces when a piece of equipment is travelling around the work site. From a wheel perspective, turning (or twisting) generates the highest forces that the wheel assembly must support. This puts the greatest amount of stress on the wheel center as well as the bolts or studs holding the wheel to the hub. Other dynamic forces would be :
The dynamic and static forces from the equipment and driveline are passed through the flange and bead seat surfaces of the tire and rim interfaces noted as “A”.
There are no mechanical fastenings of the tire to the rim. Frictional forces generated by the inflation pressure on inside of the tire holds the tire in place and resists circumferential, transverse and lateral movement. More air pressure means more fictional force to resist the dynamic forces. Less air pressure means less resistive forces.
The bead seat area of the interface has additional features to aid in resisting indexing. The bead seat area of the tire is designed to have a certain amount of interference fit with the bead seat of the rim.
The interference is to create an air seal in the static and dynamic state and to aid in stopping circumferential and lateral movement of the tire bead areas. Knurling is an added feature to provide a mechanical means of holding the bead in place from circumferential movement.
Generally, the tire tread does not slip on the ground. While this can happen in emergency braking or other situation, the tire generally has good traction with the ground. Radial tires (seem to) have improved traction characteristics with construction and mining tires. The limitation of the tire and wheel system for transmitting torque to the ground is the tire and rim interface(s).
Anything that reduces the frictional forces of the inflated tire will allow or contribute to tire indexing or tire slippage on the rim. Even with ideal conditions between the fit of the tire to the rim bead seat surfaces indexing can still occur.
One of the simplest issues that can contribute tire indexing is tire air pressure that is too low. As mentioned above, frictional forces between the tire and rim bead area resist the dynamic forces that cause indexing. If the air pressure is too low, then the tire can move. Low air pressure can occur because of poor maintenance practices of a work site, or operating the tire with air pressures that are too low for the application. The following practices will help to avoid or minimize tire indexing.
Another universal cause regardless of the application is using too much tire lubrication when fitting the tire to the rim. A tire lubricant is used to reduce the frictional resistance of the tire beads on the rim bead seat surfaces so the tire beads will slide into the correct position. It is important to follow the tire manufactures tire mounting recommendations. It is also important to:
If too much lubricant is not good, insufficient amount of tire lubricant can be equally bad. If the tire does not slide onto the bead seat surface of the rim, then the tire beads may not be positioned as intended. If the tire beads are not in the correct position then the performance and durability of the tire will be impacted. Additionally:
As mentioned above, it is important to follow the tire manufacturer’s mounting recommendations and procedures.
Assuming we have used the correct amount of lubrication, the next issue in mounting the tire that can contribute to indexing is a tire bead that is not properly seated. It was noted above, that insufficient lubrication can keep the tire from seating. Insufficient air pressure (too low) to “seat” the beads can contribute to tire indexing because the tire bead will not be in the correct position on the rim impacting the interference fit and resulting in insufficient frictional forces resisting drive or braking torques. Most tire bead areas are designed to have an interference fit. Extra force is needed to push the tire into the correct position. The “seating pressure” is generally higher than the operating pressure for the tire. Seating pressure vary depending on the type of tire.
During the mounting process, before the assembly is inflated the driver keys must be installed. The outboard drivers are intended to stop the rim components from rotational movement. Many times, the keys are missing to begin with and they are missed as one of the steps for mounted a new tire on the rim.
With any problem solving activity, all aspects of the issue should be evaluated.
* Used with permission from Tire and Rim Association.
Below is a method used for measuring the rim bead seat diameters. Not typically available at the field level but is used at the factory level to verify dimensions.
* Used with permission from Tire and Rim Association.
* Used with permission from Tire and Rim Association.
Every brand of tire is designed and engineered to provide excellent durability and service life for the desired application. Each Engineering group has their own set of design standards and design principles that they believe are correct for a particular tire/application. The resulting differences can be observed in how the tires perform in the field and fit to the bead seat surfaces. With tire indexing, some brands or sizes within a brand can be better choices to minimize or eliminate tire indexing for the application. Factors that have an influence on tire indexing are:
The manner in which the equipment is operated can have an influence on tire indexing.
Equipment manufactures make a good attempt to have the various components matched so the operators have a good experience operating the equipment. However driveline efficiencies and tire technologies have improved, the drive and braking torques being passed to ground has increase. This is good for productivity of the equipment, but the forces being applied can be greater than the tire and rim interface can resist. In these situations it may be necessary to consider moving to an assembly with a larger bead diameter.
Tire indexing is an action that normally occurs in such small, minute amounts that it can be virtually undetectable unless the tire and rim components are marked on the tire, flange, bead seat band and rim/wheel. This way you can witness the physical movement of the tire and the wheel components.
The tire, side flange, bead seat band gutter band and hub have been marked prior to a tire indexing study. The paint marks are all aligned at the start of the evaluation.
A tire and wheel assembly component after the assembly has been used.
Tire indexing is virtually impossible to stop unless all the factors that cause it are addressed properly. The "tire is going to move no matter what you do". The question is, “how much”?
The term “fretting damage” had been mentioned above as a consequence of tire indexing with multi-piece rim and wheel assemblies. Fretting is an engineering term which describes the damage to contact surfaces when they are subjected to contact pressures and exposed to repeated movement (slippage) or vibrations. The movement does not need to be large, repeated minute motion is sufficient for fretting damage to occur.
Mr. Len Hensel, BSME, MS-PDD
Len has over 39 years of industry experience in providing wheel system solutions for the mining, construction and agricultural applications. He has worked extensively with the entire major off road equipment manufacturers and off road tire (OTR) companies to provide designs that meet the needs of new applications, pushing the envelope for greater load capacity and durability. He has worked in leadership positions in off the road wheel industry new product development, application engineering, new design validation, research and development projects, and quality assurance. He is a member of the Society of Automotive Engineers (SAE), participated in development of international standards (ISO) related to off the road wheels, and a past member of the Tire and Rim Association (TRA) representing the rim and wheel industry manufacturers.
Contact: [email protected]
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.
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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.