Tires: Doing the Groundwork

What were the design engineers waiting for before they designed those huge trucks with capacities of several hundred tons? Tires. They waited until such companies as Michelin had developed the strength and flexibility necessary to support the vehicles and their loads. What is one of the most common causes of downtime at construction sites, especially at those sites where there is sharp debris scattered around? Tires. There are solid (as opposed to pneumatic) tires available, as well as sealants that have proved their ability to negate punctures, but construction workers can prevent some tire damage through good housekeeping at the site and by treating tires as if they were as important as booms, buckets, hydraulics, and engines. Tires are that important to contractors and anybody else who uses vehicles.

The manufacturers contacted for useful information about tire care all referred us to the Rubber Manufacturers Association in Washington, DC (www.rma.org), saying that a large amount of useful information is available for contractors and other tire users. The association has many publications, including those for truck tires and off-highway tires, and more than 20 bulletins covering such topics as retreading and repairing shops, tire explosions, inspection procedures, the misapplication of tires, and flammable substances in tires. The association’s publication, Care and Service of Off-the-Highway Tires, addresses underinflation, overloading, types of load scales, speed, grade, length of haul, curves, and demounting techniques for rims. Your tire distributor can also likely acquire this helpful information for you.

For vehicle and equipment drivers, tires are their contact with the ground, sometimes several feet below them. Tires are the workers that keep them moving safely and in reasonable comfort to the right place at the right speed. The tires of any construction vehicle or machine are expensive components, and their design and quality have improved dramatically, but contractors should accept that much of the responsibility for keeping tires in good condition is theirs. It’s not as if the necessary care and maintenance are difficult. When you weigh the time spent in tire care against the costs of downtime or components ruined long before their scheduled time, there is no argument. However good the tires are when you buy them, they will not respond well to negligence or abuse. “The key is checking tires regularly,” advises Vickie Johnson, market segment manager for the Earthmover Group of Michelin North America headquartered in Greenville, SC. “Routine management improves operating efficiency, promotes higher levels of productivity, and eliminates preventable major repairs.” All of those benefits add up to a better business.

Tire manufacturers (such as Michelin, Continental General, Goodyear Tire & Rubber, and Bridgestone/Firestone) recommend simple, regular maintenance throughout the construction season. Before operation, a visual inspection of the tires will show signs of irregular wear in the tread or on the shoulder of the tire. Keep an eye open for bubbles or bumps caused by foreign objects or air infiltration. If there are any, have the tire repaired before they lead to tire failure. Try to impress on your personnel that tire failures are not only expensive, but they can also be dangerous to drivers and operators. In fact, they are hazards to everybody at the site, because tires do not always go flat in a peaceful, gentle way. If you notice deep cuts, cracks, or other major problems during the visual inspection, don’t operate the vehicle or machine and don’t let anyone else operate it. A qualified service person should evaluate the severity of the problem and make the proper repairs. Unskilled people should not repair tires for the obvious reason that an incorrectly or badly repaired tire can cause even worse problems. Tires are able to continue working reliably and safely after damage is repaired correctly, so don’t trust that repair to somebody who just happens to be handy and not too busy at the time. (And you have priced tires lately, haven’t you?)

The correct air pressure is important to every tire. Check for the recommended tire pressure every day on vehicles and machines in constant use. This is not a visual check, but it takes only a matter of seconds to check each tire. It involves more than the driver or operator thinking the tires look good enough. The owner’s manual will tell you the correct pressure based on a standard load, but your tire-distributor representative should be able to tell you the best pressure for the tires at your site and for your specific applications. Obviously you should never operate a vehicle with flat tires. Nor should you operate one with distorted or damaged rims or wheels, cracked studs, or missing bolts, because the next level of damage will probably affect the entire vehicle or machine. A well-planned and faithfully followed tire and wheel maintenance program might be your least expensive insurance policy for vehicles and drivers.

“The most important aspect of tire maintenance is maintaining correct air pressure,” stresses Jack Dutcher, national engineering manager for Bridgestone/Firestone Off Road Tire Company headquartered in Nashville, TN. “Since it is actually the air pressure in your tire that carries the load, you must make sure that you have enough air pressure, but not too much. Too much can cause flexing in the wrong areas, with the casing becoming rigid and susceptible to rock cuts and impacts.” He suggests that users check a tire when it is cold, meaning when it hasn’t been operated for 24 hours. That might not be possible, so it becomes important to check all the tires on a vehicle at the same time. “All tires on a machine should be compared to each other so that you can spot abnormalities,” advises Dutcher. “A tire that is operating at a higher or lower pressure than the others on the same machine indicates a problem should be investigated.” There are other aspects, apart from the tires themselves, that can affect performance. Are the loading and dumping areas causing rock cuts? Do the haul roads have super-elevations to maximize speed, minimize spillage, and minimize excessive tire forces? Is alignment part of your maintenance routine? What about springs and struts? Uneven springs or struts can cause an uneven load distribution that can be worse than a poorly placed load.

Visual inspection of tire pressure is not accurate enough because some of today’s tires operate at air pressures as much as 15% or 20% lower than yesterday’s standards. Letting a worker judge the suitability of a tire by his impression (probably based on past, and now inaccurate, experience) of the tire’s pressure could cancel all the benefits of the new lower-pressure tires. Caterpillar chose Michelin 44/80R57 XKD low-pressure-technology tires for its 240-ton-class 793 haul truck, with one of the main reasons being the influence of low tire pressure on the life of the tire. After 5 million tire miles and 100,000 truck-logged hours of actual use at various sites in North America, the 44/80R57 XKD demonstrated up to a 15-20% reduction in overall cost per ton; an increased resistance to cuts, punctures, and tears; and better gradeability and machine handling. The comparison is made to a Michelin tire of previous design. The low pressure is only one aspect of the advanced design of the tire’s structure, and the same good results would not occur by just lowering the pressure on a different tire already in use. Checking the tire pressure is not a casual inspection; it is adherence to a balanced technique for saving money.

If the alignment is wrong, the tires will be unable to do their job as designed and will suffer unnecessary wear. Continental General Tire has an interesting indicator that tells drivers and fleet managers if there is an alignment problem and does so soon enough to do something about it. The Visual Alignment Indicator is a set of five small sipes, or grooves in the tire tread, molded to various depths. These sets are spaced evenly around the tire on both shoulder ribs. Naturally, the shallowest grooves wear away before the deeper ones, and by comparing the indicators on the inside and outside shoulder ribs, the user can detect uneven wear (in as little as 3,000 mi.).

In addition to their increased load capacity and lower pressure, the tires developed by Michelin for those huge dump trucks have lower profiles, which makes them radically different than conventional types. The lower profile limits the external diameter and offers two obvious advantages. The vehicle and loading heights are kept to a minimum so that the center of gravity and the dynamic load transfer are kept low, which should improve vehicle stability and safety. And although they have increased carrying capacity, these tires have diameters similar to existing tires, which means that users can transport and handle them using existing equipment.

Moving and storing tires are also key factors in a practical maintenance system for vehicle and machine owners. Grabbing and lifting tires with a crane hook can damage the bead area, so it is better to lift them by means of flat straps under the tread. Heat close to tires can cause damage (even to the extent of explosion). When work is required on parts of the wheel (e.g., the rim) and involves such procedures as welding, remove the tire before proceeding. The same aversion to heat has also influenced the design of tires. The radial construction of tires (where the tread and sidewall function separately) claims cooler running as one of its advantages over bias construction (in which the crown and sidewalls are formed by the same ply construction). For storage, too, coolness is important to tires. Exposure to direct sunlight can cause premature aging; arc-welders, mercury vapor light bulbs, and ultraviolet rays are also unkind to tires. A cool, dry place is ideal for storage. Stand the tires upright (on their treads), not in stacks where the bottom tires can be weakened by the weight on top of them.

Contractors know that the footprint of steel or rubber tracks on excavators and cranes can play a significant role in the maneuverability, stability, and safety of the machines; it is the same with tires. The footprint of a tire is the area of tire tread that contacts the ground. A large footprint can improve both traction and flotation so that the tire rides on the surface of the soil to reduce soil compaction and slippage. With radial tires, the sidewall deflects and places more of the tire on the ground to create a larger footprint and spread the weight of the machine or vehicle. The improved traction and flotation can increase productivity, especially on rough terrain. It is the flexibility of the radial tire, rather than mass or rigidity, that is its true strength, because it allows the tire to sustain less damage when going over sharp objects and helps absorb shock. With fewer punctures, the tire will last longer.

A better footprint is the goal with the track option offered by the Melroe division of Ingersoll-Rand for its Bobcat skid-steer loaders. In most seasons and on most ground, the standard tires for these loaders are perfectly adequate, offering good traction but not damaging the surface. With tracks replacing the standard tires, however, the loaders can cope with poor ground conditions common to some months and thereby extend the working year for the machines. The tires do most of the work most of the year, but they can be replaced for special projects and then go back to work as the season changes. Sometimes tires are not the ideal solution for construction machines, because tracks (especially rubber tracks) can also provide a better footprint on sensitive ground, like that in some residential work. The ground pressure of ASV’s Posi-Track HD4500 Series loader is only 3 lb./in.², even though it is a heavier model than the successful 2800 Series. The loader comes standard with a universal quick-attach suitable for dozens of attachments and can have engine power of either 85 or 115 hp. This loader, with rubber tracks and a light footprint, can travel across finished surfaces, such as lawns and golf courses, without causing costly damage. It also moves through mud and swamps or up steep inclines without difficulty.

Haul trucks working constantly at quarries and mines experience some of the worst road conditions for off-highway vehicles, but the same problems can exist for contractors at remote construction sites, especially for the transportation of materials and equipment to and from those sites. German manufacturer Erlau has designed and produced tire-protection chains for several decades and has developed the Plus-Link, a patented design that projects at right angles to the tire and is secured to rings that are parallel with the tire. “A combination of transverse and angled grooves with a stepped configuration provides outstanding grip and creates larger surface areas of hardened steel,” explains Jürgen Beer of Erlau. “Pressure on the tire is supported and absorbed, thereby ensuring the utmost durability throughout its entire service life. The broad contact area of the link reduces the ground pressure, while the smooth shapes of the chain contours present no places for rocks to snag.” Erlau asserts that the cross-section of this new link absorbs tractive and torsional pressures relative to the adjoining ring. Another design from Erlau has been the Granite-Link, with a ring diameter of 0.8 in., for large machines with gross weights of more than 150 tons.

Chains are not all the same. Different configurations tend to be appropriate to different ground conditions or machine styles. They can serve on a variety of construction and quarry machines. Potential users should check with experienced owners and with the manufacturers to ascertain which types of protection and which configurations might be the most practical for their particular vehicles, machines, operations, and site conditions. Can chains save the user money? The Australasian office of RUD Chains reports that tire costs have been reduced by 76% at a large iron-ore mine in Western Australia where chains have been fitted to the front wheels of a CAT994 wheel loader with 50/80×57 tires, directly saving the company over $450,000 per year in operating costs and increasing machine availability. “Perhaps one of the most important reasons for the consideration of a chain fitting is to guarantee the maximum availability of major quarry production units, like a face loader, at all times,” suggests Peter Nuttall Jr. in an article from RUD Chains about the applications and developments in tire-protection chains. “Chains do not interfere with the many advantages that come with using pneumatic-tired loaders, such as the softer ride, the flexibility, and the better mobility. But at the same time, they give excellent protection from expensive damage and downtime by completely protecting the vulnerable tread and sidewall areas of the tires.”

RUD recommends that an experienced chain fitter handle the fitting and train site personnel in maintenance procedures. Trained chain fitters can carry out fitting quickly and efficiently, with little disruption of the owner’s operations. For example, to fit two chains to a CAT 988B would take approximately three hours. No special tools or equipment are required to fit or maintain tire chains. “The chains can be fitted over any tire, no matter whether it is an L3, an L5, brand-new, worn, or slicks,” Nuttall explains. “The only recommendation is that the tires have a sound casing with no serious cuts or damage.” The tire pressures and operating style of the loader remain largely unchanged with a chain fitting, but it is preferable to maintain low speeds to ensure maximum lifetime of the chains.

Debris from demolition, chunks of discarded metal, nails, concrete, and broken glass and wood-all hostile materials lying on the ground-have damaged too many tires with punctures, preexisting tire damage, or excessive wear. Invented in Australia, the AirBoss puncture-proof tire system has steadily gained popularity worldwide. These solid tires carry machines across sharp, cutting, abrasive obstacles with less likelihood of failure than pneumatic tires. AirBoss Tyres reports that contractors and operators have also said that the tires give a better ride on such rough terrain, but the most common praise seems to be for the costly downtime avoided by having no punctures on equipment that must be busy to be profitable. SETCO uses 100% natural rubber with shredded wire (of 70,000-psi tensile strength) to manufacture its solid tires. These tires have been successful with wheeled loaders at construction sites where ground debris can destroy standard tires and at such locations as landfills and scrap yards, where the environment is hostile to tires by the very nature of the materials there. SETCO solid tires also work on skid-steer loaders (such as those from Case, Gehl, and Bobcat) and backhoes (from Caterpillar and Deere, for example). Solid tires can run for thousands of hours.

The heart of the AirBoss system is the 10-16.5 tire for skid-steer loaders, but new sizes match almost all skid-steer makes and models. For backhoe/loaders, AirBoss has developed a one-piece 12/12.5-18 tire for the machines’ front wheels, a size that can also fit site dumpers that have an operating weight of up to 5 tons and small wheeled loaders up to 10 tons. In addition to being puncture-proof, the heat-resistant material used in the manufacture of this tire allows a machine to travel on the highway with no heat buildup. Small and medium trenching machines also use these tires. AirBoss hopes to offer tires suitable for all construction machines working on abusive ground, and it now offers one-piece cushioned tires (26×12.00-12 or 23×8.50-12) to give good flotation, extra stability, and a smoother ride for mobile access equipment such as self-propelled access platforms and scissor lifts. There is also the 17.5-25 earthmoving tire suitable for larger materials-handling machines, such as the Volvo L70 wheeled loader. The significance of the latter tire model is that it places the puncture-proof system into that large market sector that includes machines with operating weights between 8 and 12 tons. With this earthmoving tire, as with other segmented tires, damaged segments can be replaced individually even when the tire is fitted to the host machine.

Ultraseal is a preservative for increasing tire longevity and safety. “It will convert any pneumatic tire into a self-sealing tire that will maintain air pressure and coat the inner surface of a spinning tire without succumbing to the shearing stress associated with centrifugal force created within a rotating tire,” explains Liz Aguirre, president of Ultraseal International Inc. in Los Angeles, CA. Ultraseal has been successful for 30 years, with recommendations from users as diverse as state Departments of Transportation, landfills, school districts, construction companies, public utilities, and mining operations. The process involved is chemical. Once Ultraseal is installed, it lies dormant at the bottom of the tires until the tires have been installed on the vehicle. Once the tire has been driven a minimum of 3-5 mi., the sealant disperses throughout the entire inner air cavity of the tire and wheel. The flexing of the tire and normal heat buildup allow Ultraseal to locate and eliminate common air-loss problems (usually called porosity air migration and bead leaks). When a tire is punctured, Ultraseal coats the surface of the penetrating object to prevent air loss. When the object is removed, the rubber recovers and the wound immediately closes. Normal operating temperatures for this product are -40° to +302° F.