Tire and track manufacturers are developing new products for special off-road applications in the construction industry. The result is potentially longer life and lower life cycle costs for these seemingly mundane, but key, elements of any earthmoving operation.

By Charles D. Bader

Why another article on tires? Because they represent essential considerations to construction operations, and the earthmoving-vehicle manufacturers are well aware of that fact. Don Stretch summed it up effectively once when, as senior sales consultant for Caterpillar in Peoria, IL, he stated: "Proper tire selection, application, maintenance, and operator training are very important factors in earthmoving economics. Wheel tractors, loaders, scrapers, trucks, motor graders, et cetera are earthmoving vehicles whose productivity and payload unit cost depend greatly on tire performance."

And Cat continues to stress that fact, sometimes surprisingly so. Recently the company introduced a remarkable feature for wheel loaders called Aggregate Autodig. Using operator-programmed controls, the system permits consistent full loading of buckets with sand or aggregate. The operator approaches the stockpile normally, and when the system detects that the bucket has contacted the pile, a quick lift is automatically initiated. Then the machine goes through an algorithm of lift-and-tilt motion to finish loading the bucket. The entire process results in full bucket loads in a matter of a few seconds. In pointing out the benefits of Aggregate Autodig, Cat lists maximizing the payload per bucket, reducing operator error and fatigue, increasing productivity, and - you guessed it - longer tire wear.

According to Cat's Bill Campbell, "Tire wear on wheel loaders is most affected by operator technique and traction aids [for example, limit strip differentials, no-spin differentials, and traction control systems]. However, while these traction aids can improve traction in poor underfoot conditions, they can actually increase tire wear in good conditions due to tire scuffing caused when the machine articulates. With the Aggregate Autodig system, the programmed quick lift loads the front tires, thereby improving tractive effort. With this automatic loading of the tires at the beginning of the loading cycle, tire slip is minimized, thereby increasing tire life."

With this kind of emphasis placed on tire life and maintenance, it is not surprising that the tire manufacturers all have aggressive programs to improve tire performance, introducing new models to enable contractors to gain the best possible cost-effectiveness for all their earthmoving vehicles and all their principal applications.

What's New in Pneumatic Tires?

Segmented tires on a Case skid-steer.

Dennis Munns, manager of material handling equipment for John Deere in Moline IL, states, "Before you can even start talking about new tire developments, you should stress that radial tires are not being used nearly enough in the construction industry. I'd say that 80% of all construction vehicles should be running on radial tires and the other 20% should only be using bias-ply tires if they have special applications where rocks and other debris might get caught in the sidewalls of a radial tire."

Chris Rogers, Bridgestone's general manager of marketing in Nashville, TN, agrees with the choice of radial tires for most construction applications and says the construction industry probably uses a higher percentage of bias-ply tires than any other industry. But, he contends, "The larger earthmoving equipment found in quarries and mines have now become radialized with very few bias tires being used. And we see a continuing shift to radials for smaller machines, such as graders and scrapers. There are more manufacturers of radial tires addressing the construction market now, and this, along with the lower operating costs associated with radials, is accelerating the industry's conversion to radials."

Regarding the most significant new trend in tire design for construction vehicles, both Rogers and Munns agree that it is the increasing popularity of low-profile radial tires. "They have been out for three years now, and it is only recently that they have become popular among contractors," Rogers says. "Not only is this acceptance trend caused by greater familiarity with a new product, but it is being driven by performance issues. For loader applications sensitive to stability needs, low-profile technology improves stability by lowering the sidewall height of the tire without changing the outside diameter. This is accomplished [by] changing the aspect ratio to create a wider footprint and lower sidewall [and], in some cases, sizing the rim diameter to create a lower tire sidewall height. Stability is improved in this instance through reduced sidewall flex and movement. The cost differential is only 10% to 15% now, and that should narrow as sales volume increases."

That already might be happening. Tomas Bennett, market segment manager of Michelin North America in Greenville, SC, reports that Michelin's new XLD 65 low-profile radial tires, designed for small- and medium-wheel loaders, are priced only about 3% higher than comparable conventional radials. "They are taking the industry by storm now," he claims. "The architecture adds extra stability, gripping, and traction that help loaders increase productivity through faster acceleration, increased cycle time, and greater bucket penetration and fill. The numbers speak for themselves. Compared to our Michelin 23.5R25 XHA, which has proven to be the industry's most cost-efficient tire for wheel loaders, the XLD-65 provides 12% increase in ground contact area, 24% lengthening of tread pattern edges, and up to 10% greater bucket penetration and fill with the additional gripping and traction provided by this new 65-series tire.

"What's more," he continues, "the XLD 65's low-profile design allows loaders to accelerate faster and with less effort, allowing operators to make more trips faster, increasing productivity. Also, the tire's increased working deflection and reduced sidewall height provide excellent shock absorption. The lower center of gravity and innovative low-profile architecture reduce vertical oscillations, decreasing rolling resistance and pitching. These features also provide better lateral stability, especially with a loaded bucket."

Each XLD tire adapts easily and cost-efficiently to all existing loaders, including the same wheel size, rim, side clearance, bucket width, and vehicle transmission. However, Bennett says, "in new vehicle sales, OEMs [original equipment manufacturers] tend to recommend the use of our larger-rim tire for even better traction."

Bennett cites two other new Michelin tires that he says have gained good acceptance by contractors. One of them seems an unusual marketing choice: the XTS, an all-new radial tire specifically for midsize scrapers that, he reports, provides long tire life, resistance to damage, and a large ground-contact area.

"Compared to our previous scraper tire, the XTS has 8% more rubber in the tread and shoulders, which, when combined with the square shoulder design, provides excellent protection in tough operating conditions, therefore helping to decrease downtime and improve cost per hour. It also delivers excellent flotation, which contributes to its exceptional performance. The tire's cool operating temperatures and low susceptibility to damage from impacts and penetrations help increase productivity, while the low-rolling resistance helps improve fuel economy. All of these attributes help deliver low operating costs," Bennett maintains.

Michelin's introduction of a new model specifically for the limited scraper market must have seemed risky, but the move appears to have paid off. Out for a little more than a year, the XTS already has generated "a big increase in sales" over the scraper tire it replaced in the Michelin line. And it earned the company one of Construction Equipment's Top 100 New Products awards.

Also earning a top-100 award was Bennett's third choice, the Michelin XZSL Stabil'X' "The first and only radial tire for skid-steer loaders yet on the market." Bennett says the XZSL is a steel-belted radial tire with a steel casing and special rubber compounds that increase resistance to cuts and abrasions for fewer flats and longer tread life. It delivers enhanced traction and handling and a smooth, stable ride. The XZSL also features an aggressive, nondirectional tread pattern that leaves fewer marks on concrete and pavement.

This also was a bold marketing move because the skid-steer market traditionally has been a price-sensitive one that almost exclusively uses low-cost bias-ply tires. However, Bennett explains, "Michelin market research identified niche skid-steer market segments, such as asphalt work, demolition, and concrete applications, where bias-ply tires tended to wear out in as little as three months. Because the XZSL has been outwearing bias-ply tires in these applications by three to six times and is less expensive than foam-filled tires, it has proven to be quite popular in these severe environment applications.

"And what's more, it now appears that the XZSL will be ideal for the new compact mini-loaders in these applications."

Selecting the Right Tire

The expected load on each tire heavily influences how the best tire size and capacity for a given application are determined. This depends on the total vehicle weight and weight distribution. The total weight is the sum of the weight of the typical load of material being hauled and the bucket size added to the empty weight of the vehicle. The weight distribution between the front and rear tires varies, depending on the vehicle. For example, when a wheel loader is fully loaded, it is estimated that 80% of the total weight will be borne by the front tires and only 20% by the rear tires.

Comparing the resultant calculation of the tonnage each tire can be expected to carry with the tire manufacturers' tire-load and inflation charts will determine which tires have the capacity to handle that load. "You might find that your first choice of tire size does not have the capacity to handle the loads you're demanding," Munns warns. "So you'll be forced to consider a larger-tire option. Or perhaps you'll find that smaller loads will handle the loads nicely. The point is, these charts will give you firm capacity numbers on which you can base your final decision."

Temperature is another vital parameter in selecting the right tire for a given application. According to Caterpillar Performance Handbook, the ton-mph formula was developed to predict tire temperature buildup. This system is a method of rating tires in proportion to the amount of work they can do from a temperature standpoint. It utilizes the product of load x speed to derive an index of tire temperature buildup. Maximum tire level-off temperatures of 225°F for fabric-cord tires and 200°F for steel-wire tires are the limits that Cat recommends. Even at these temperatures, failures might be initiated by overstressing the tires. Some companies rate fabric-cord tires at 232°F or, on occasion, as high as 244°F. These higher temperature levels are questionable under average field conditions.

Goodyear has developed a measure that it calls the Work Capability Factor (WCF) to help select the right tires for load-and-carry loaders, which increasingly are being used as transport vehicles. When a loader is used to haul material farther than 50 ft. at speeds above 5 mph, the WCF should be applied (as described in the sidebar) to calculate the right tire for that application.

"To find the right tire for the application," Goodyear advises, "consult the published Work Capability Factors for haul lengths of less than 2,000 feet one way that have been established for each size and type of Goodyear dozer and loader tire. Then select the tire whose WCF rate meets or exceeds the job WCF requirement. If you have a multiple choice of tires whose WCF rate is more than the job requires, always select the tire with the lowest rate that will meet the requirement. In this way, you will always have the optimum tire - that is, the best tire for wear and durability, as well as being adequate for heat resistance."

Overcoming Excessive Flats

Flat tires are an annoying interruption in any situation, but when they occur too frequently and/or at a remote job site, they can be prohibitively expensive. Based on feedback from contractor customers, AirBoss in South Haven, MI, calculated the potential cost to a contractor when a flat occurs in the field. Table 1 shows the calculation for a Bobcat 800-series machine. The table assumes a job site that is not a great distance from a tire dealer so that the repair, including drive time, could be completed in two hours. Obviously this time could be much greater for operations at a remote drive site. Similarly the assumed hourly wage, including benefits, was just $12.50, and this will be much higher in many parts of the country. Even using these conservative assumptions, however, the total cost of each flat tire was calculated to be $225.

Because of these persuasive economics, contractors who work in environments where flats are quite common are likely to consider flatproof tires. One such contractor is Craig Kucharski of Craig Excavating Co., who reports that his vehicles were "continually climbing curbs and constantly encountering nails, metal, pieces of wood, concrete, rocks, and fallen trees. In fact, I spent $5,000 on tire repairs and replacement tires in the 12 months prior to installing AirBoss. Besides eliminating flat tires and eliminating my stress worrying about flat-tire downtime, the AirBoss tires are wearing great and the traction is excellent."

Although Kucharski settled on AirBoss segmented tires, he had a variety of flatproof tire types from which to choose. One such solution is to use totally solid rubber tires, such as those offered by Setco of Idabel, OK, and AirBoss. Setco Sales Manager Stephen Hadley describes his company's solid tires: "The 100% natural rubber is adhered directly to a rim. The rubber is reinforced with shredded, 70,000-psi tensile-strength wire for strength, cut resistance, and extended tire wear. If you do cut the tread face of a Setco tire, you've simply added another tread void for traction."

Hadley concedes that solid tires have not been widely used at construction sites other than demolition sites. "Solid tires simply don't have the traction that a typical construction site requires." AirBoss President Jerry Van Vlack agrees that solid tires - including his - don't have much place in the construction industry. He is convinced that his company's segmented tires are the answer to ending flats at even the most severe construction-site environments.

"A segmented tire," he explains, "consists of a large steel rim onto which 20 or 22 thick segments of rubber tread are bolted. Not only are these segments much thicker than typical pneumatic tire treads, but individual tread segments can be replaced as they wear out. Our segmented tires have an average of 55% greater traction and double the shock absorption of comparable-size pneumatic tires. And, of course, they are completely puncture-proof."

AirBoss's most popular segmented tire is its Altrakka III, which is used for grading and excavation work mounted on skid-steer loaders, backhoe loaders, tool carriers, wheel loaders, or trenchers. "It offers a flatproof solution to contractors who are having flat problems with standard pneumatic tires," Van Vlack says. "We encourage prospective buyers to enter their operating cost data into our flat-tire cost analysis form. Contractors who normally operate at sites covered with rubble, rebar, nails, and the like are astonished at how much they will save just by switching to our puncture-proof segmented tires. Avoiding as few as two flats per tire over the 18-month tire life will completely offset the higher initial price of Altrakka III tires." (This is corroborated by the data presented in Table 1.)

So far AirBoss sells primarily to end users, although its tires also are available to OEM dealer networks. In addition, equipment rental companies are becoming more of a market for AirBoss segmented tires. George Gillis, a branch manager for Hertz Equipment Rental, provides insight into why rental companies are interested: "We installed four 17.5x25 [AirBoss segmented] tires on a 621C Case front-end loader. The incidents of flats and downtime were eliminated. Prior to installing the AirBoss tires, the machines had 30 flat tires in a three-week period. Now this has been a trouble-free operation for over 1,000 hours."

"They can and do charge a rental premium on vehicles with segmented tires," Van Vlack points out, "and they are attracted by the cost-of-ownership savings as compared to foam-filled tires, which are really the main competition for segmented tires."

Neil Ganz, managing director of Galaxy Tire West of Hayward, CA, undoubtedly would challenge that statement. Galaxy produces a foam-filled punctureproof tire, although the company uses a polyurethane fill that it insists is much superior to conventional foam fill. "Our Soft Flex-Super Fill tires also provide 100% protection against flats, but they ride like air-filled tires," Ganz claims, adding that polyurethane-filled tires cost more than pneumatic tires, but they provide a number of offsetting savings:

• They substantially reduce downtime by eliminating flats and reducing the shocks and stresses to the equipment.
• They eliminate the need to constantly monitor tire air pressure. Once filled with the polyurethane, they will remain pressurized to the correct pressure for the life of the tire.
• They can be retreaded three times without any deterioration in the performance characteristics of the fill.

"Galaxy's poly-filled tires are approved for use by every major equipment manufacturer that has tested them, as well as by suppliers of critical components, such as axles. What's more, they do not void the warranties of these OEMs. And both the cost of the tire and the cost of the fill are covered by Galaxy's warranty, which extends through multiple retreadings."

Now Galaxy is branching out into other specialty tires. Its new L-6S super heavy-duty bias-ply tire has a 40% deeper tread than does an L-5, but its overall diameter is exactly the same. With 24 actual plies, it can withstand severe cuts that would cripple a tire with just 12 actual plies.

"Originally we planned to market the L-6S as a poly-filled tire," Ganz recalls, "but then a customer, American Ref-Fuel, changed our minds. For years, American Ref-Fuel foam-filled every tire. When we came out with the L-6S, they decided to test the first set to see if the added depth and additional plies would result in less severe cutting and, therefore, less downtime. The results were so positive that today they run 12 Volvo machines without foam fill, saving thousands of dollars in the cost of the foam and repairs to the machines.

"Moreover, with its deeper tread and a super-strong carcass, the L06S can be retreaded too. So far every Galaxy L-6 tire has been retreaded an average of three times. With this added life, we are convinced that the L-6S has the lowest cost per hour of any tire in the world used on these super-severe waste operations."

How About Tracks?

In the article "Getting Over the Terrain: When to Use Tracks or Tires" in the March/April 2000 issue of Grading & Excavation Contractor, John Deere's Kirk Kessler stated that determining whether wheeled or tracked equipment should be used for a specific job is a pretty simple thing. "If you've got a situation in which you're either working on grades that are too steep for a rubber-tired machine to negotiate or your ground conditions are so poor that you don't have the tractive effort and get stuck too easily with the rubber-tired machine, you use tracks. If you're concerned about ground compaction - you don't want to compact the ground too much - then switch from tires to tracks."

But which tracks? Steel is the dominant material for tracks because steel tracks can provide the traction needed for most applications. In many instances, however, either rubber or polyurethane pads or rubber tracks are desirable in order to minimize the impact on the surfaces that the vehicles operate on. "If you're always working in dirt, you won't need to protect the surface," maintains Barry Stoughton, president of BLS Enterprises in Elk Grove Village, IL. "But if you're working in an area of paved streets, on asphalt or concrete, or even on grass, steel tracks could tear up the surface that you're working on. That would dictate the use of rubber pads or polyurethane-covered steel pads.

"While rubber pads have certain applications, they have a tendency to chunk out in rough environments. In contrast, polyurethane has a longer life, lasting two to three times longer than rubber pads. The polyurethane-covered steel pads wear like they're being sanded down versus chunking out - but they are significantly more expensive."

Bridgestone Industrial Products of America markets continuous rubber tracks and rubber pads. Drew Minwegan, director of OEM products, explains the rationale for rubber tracks: "Tires and steel tracks each have unique features [that] can make them ideally suited to specific applications and environments. However, a gap exists when equipment and the operating environment would be best served by a blend between these two drive mechanisms. This gap is effectively bridged by the combination of the positive attributes of both tires and steel tracks by utilizing rubber tracks. These tracks enable a machine to operate in conditions where low ground pressure and high tractive effort are needed while minimizing the damage to the operating surface."

Offering excellent traction and durability, continuous rubber tracks appear to be a viable choice for any compact construction machine. In the construction industry, they are used on skid-steer loaders, mini-excavators, asphalt pavers, dozers, tracked carriers, and boring and trenching machines.

"Mini-excavators have become the largest category of construction vehicles using our rubber tracks," Minwegan says. "Long popular in Japan, these vehicles are now a rapidly growing portion of the construction equipment base in North America, and our continuous rubber tracks are ideal for that vehicle size and application. Continuous rubber tracks have a metal infrastructure that is entirely embossed with a continuous rubber loop. This allows vehicles to go across finish surfaces, to eliminate track noise, and to absorb the shock from ground impact for a smoother ride."

Many aftermarket suppliers sell over-the-tire tracks and rubber track conversion kits, thereby providing users with the flexibility to convert their smaller vehicles from tires to tracks and back again. For example, Mattracks Inc. of Karlstad, MN, supplies a rubber track conversion system for 4x4 1.5-ton trucks and service vehicles. Marketing Manager Del Wright says the system is particularly well suited for providing crew access and emergency access via the four-wheel-drive trucks to and from remote work sites before any roads are in place. He claims that they work equally well in sand, mud, or snow and that a tire can be removed and replaced by a track in less than half an hour.

BLS Enterprises distributes an over-the-tire system, called Protrac, for skid-steers. These tracks use bolt-on replaceable/interchangeable pads that are fully reusable, thus allowing low-cost maintenance. The system can be provided with either (1) a rubber shoe assembly that provides maximum protection when used even on easily damaged surfaces or (2) a magnesium shoe assembly that offers better traction in muddy, swampy, or wet conditions.

While conceding the flexibility benefits afforded by interchangeable tire-to-track-to-tire systems, Minwegan says Bridgestone made a conscious decision to design and market its continuous rubber tracks as part of an undercarriage system, thus optimizing track performance. "When you put tracks over tires, you are pulling in opposition to where you need your chains to be," he says. "Therefore, we pass up that conversion flexibility and work with the vehicle OEMs so that the contractor gets an optimized undercarriage system with integrated tracks."

So there you have it. The OEMs and the tire/track suppliers are working inventively and effectively to produce products and systems optimized for each construction vehicle and each construction application. And the construction industry is beginning to respond to these developments and expanded choices and see them as a part of their overall contractor productivity enhancement programs.

Author Charles D. Bader is with Dateline II Communications in Los Angeles, CA.

GEC - July/August 2003

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