Understand Tire Ratings to Match Off Road Tires to the Application

Tire selection determines, in part, how well your earthmoving equipment can do its job. And with more applications switching to radials, the number of options you have to choose from has increased, making selection a bit more complicated.

"In the past, construction was largely a bias market," says Cara Junkins, Titan. "Over time, radials have become more readily available. They give the end user another option. But he needs to know what his specific operation is and what his risks are, then decide which will be the best tire."

Today's newer equipment is also typically larger and more powerful, yet runs on the same size tires. "As the equipment gets more powerful, you get closer to the limit of that tire," notes Steve White, Michelin. "Making the right choice is in some regards more difficult, because you have to take that important factor into consideration."

Selecting the right tire is also important if you intend to implement a retread program. "A tire's casing is approximately 75% of the tire construction weight," says Roger Best, senior field engineer, Off Road, U.S. and Canada Commercial Tire Sales Division, Bridgestone Americas Tire Operations. "Consider choosing major tire brands when purchasing new tires, because major manufacturers have invested heavily in research and development of premium casings, which are likely to be better candidates for retreading."

Equipment type and travel needs
To ensure you make the right tire choices, start by matching to the equipment type. Off-road tires are classified as "E" for earthmovers such as scrapers and articulated or rigid dump trucks; "L" for loaders and dozers; and "G" for graders.

"The forces and conditions in which each tire works are different," says White. "A loader tire will typically need more sidewall protection because of the areas in which it works. A transport tire may not have the same level of sidewall protection, but it's designed to take the stresses of the load at higher speeds. In the case of an articulated dump truck, the tires flex in different directions as it makes a turn.

"That's why it's important to have the proper tire for your application," he adds. "Each is designed for the forces it encounters."

Some manufacturers offer dual-marked tires, which are suitable for transport and loader applications. For example, an E-3/L-3 can be used on a loader or transport vehicle. "Don't try to crisscross tires unless it's dual marked," says Junkins. "If you have a loader, use an L tire; if you have an earthmover, use an E tire."

Earthmover tires also carry travel restrictions, so you will want to consider how far and how fast your equipment will be traveling. An "E" tire is designed to travel a maximum of 2.5 miles one way at a maximum speed of 30 mph; an "L" tire is designed for 250 ft. at 5 mph; and a "G" tire can travel unlimited working distances at 25 mph.

"A loader tire has a slower travel speed because loaders typically pick out of a pile and dump in a truck," says Junkins. "Because they travel at slower speeds, they can carry a heavier load. That's why it's important to match the tire to the vehicle. A loader tire's bead and carcass are designed to handle a heavier load, where an earthmover tire of the same size and ply rating won't carry the same amount of load unless it's dual marked."

If you travel further or faster than these parameters, you may want to consider a radial tire, which is more forgiving of the heat buildup created in these conditions. Radials are becoming more available and, in fact, they're all that Michelin manufactures. There are differences in the construction, and each offers advantages in certain applications.

"Investing in a radial tire in an application where sidewall cuts are the main reason for tire removal may not work," says Best. "Radial tires are more susceptible to sidewall cuts due to the flexing in the sidewall, where bias tires are very rigid in the sidewall. The radial tire has a very stiff tread due to the use of several steel belts within the construction design of the tire.

"The downside to bias is with the inflexibility comes an increase in the chance for heat and impact breaks," Best continues. "Although the bias tire can have steel belts to help protect the casing, it will ultimately not perform as long as the radial tire."

Tread depths and compounds
Within each tire classification, you have a selection of tread patterns/depths, such as E1, E2, E3, E4, etc. Essentially, tread depth increases as the number increases. For example, an E2 tire provides a nice balance between tread and void to provide good traction in sand and soft soils. An E3 tire will have more tread than void to provide resistance to rock damage, yet provide adequate traction. An E4 tire has tread depths of 150% of E3 tires for greater resistance to rock damage.

Compounds used in tire construction can also affect selection. "Certain compounds are resistant to cuts and abrasions, where others are designed for higher speeds," says White. "Generally, there are compromises. A tire that is cut resistant is typically run at slower speeds.

"You need to know where you're using the tire. Also, consider that you can reduce your speed or your load," he states. "Consider the downtime if you tear up tires. I've seen operators 'floor' the vehicle to get to the pile for loading, race to dump it, then race back to wait in line for several minutes, rather than running at a more reasonable pace and maybe waiting for just a minute or two."

Application is one of the determining factors in selecting the appropriate tread pattern/depth and compound. "Application affects tire selection because of the need to match the tread pattern with the type of service," says Best. "There is no point in putting an aggressive traction pattern tire into an application that is highly abrasive with hard, compacted roads. The converse would be applying a rock-type pattern into an [application] that has very soft conditions with lots of water and mud."

As the application changes, so should the tire choice; take running a loader in a pit operation with shotrock, for example. "Most of the time, you're loading a truck and running short distances, so an L5 bias tire with a cut-resistant tread would be appropriate," Junkins says. "But let's say you aren't loading a truck; instead, you're running 300 yds. to a conveyor. Now your decision changes because you're running further than what the tire is designed for. Under these circumstances, you would have to look at either switching to a radial, or running with a tire with a shallower tread depth and/or compound."

Admittedly, it can be difficult to determine the right tread design for construction sites, since you're faced with a "mixed bag" of applications and conditions. "Oftentimes, you're working in many different types of jobs," says White. "For one month, you might be working in muck and rock, then the next month, you might be in dry conditions."

A larger fleet may be able to set up equipment with different tires for specific applications. However, a smaller fleet may have to compromise, White notes, since it may not have the resources to change for each application. "Maybe you're in a loader application. You choose an L2 tire for traction, but you may often end up in rock, so you move to an L3. It gives up a little bit of traction to have a little more protection. That may be the better tire for you," he states. "It all depends on your needs and what you've typically faced in the past."

TMPH ratings
A professional dealer or OTR manufacturer representative can help ensure you make the appropriate tire choices for your jobsites.

Utilizing the resources of field engineers and product managers, an OTR tire manufacturer can perform an on-site TMPH (ton mile per hour) study. TMPH is the working capacity of the tire, as well as a function of its maximum allowed internal operating temperature. In simplistic terms, it's a heat index.

Several factors are used to determine the operational TMPH for a given jobsite, including load, speed, distance, number of cycles and type of equipment. Once the jobsite TMPH is determined, the correct tire can be recommended for maximum performance.

"If the tire's TMPH rating is lower than the operational jobsite TMPH, the tire is not suitable for this application, in which case a change in compound, construction or tread pattern should be considered," Best says. "However, if the tire has a higher TMPH rating as compared to the jobsite TMPH, the tire is suitable for this application.

"Jobsite conditions can also be changed or modified to adjust the operational TMPH. Reduced speeds and load reduction can be made," he continues. "But real life predicts this is unlikely. In fact, chances are better that both loads and speeds will increase compared to the snapshot time period when jobsite conditions are observed."

Thus, to ensure optimal performance and longevity, select tires that effectively match or exceed the current jobsite TMPH, then re-evaluate as conditions and/or applications change.