With approximately half of today's construction fleets running on bias-ply tires and the other half shod with radials, it's important to understand the benefits and impact on operating costs of each type. While North American construction fleets lag Europeans in the adoption of radial tires, their market share continues to grow.

"The larger the equipment, the higher the percentage of radials," says Dave Wright, manager - global OTR product support, Goodyear Tire & Rubber Co. "It continues to go toward radials. It's just a matter of how long will it take to completely change over."

The replacement market demonstrates the different adoption rates by size. "For the smaller machines that have a 23.5 R 25 or smaller, the market is about 40 percent radials, but it's climbing," says Tomas Bennett, market segment manager for forest and construction, Michelin North America. "You get into the bigger machines with a 26.5 or a 29.5 and it's about 50 percent. The large mining trucks are 80-percent plus."

This trend is being driven by the advantages of radials in many applications. "While the upfront purchase price of a radial is slightly more than a bias, in the end the total cost of ownership is almost always lower," says Rob Mills, marketing product manager, Bridgestone/Firestone Off Road Tire Co. "Radials offer lower fuel consumption, better traction and flotation and improved cut resistance in the tread area, and run much cooler than bias."

"Radial advantages are pretty much across the board," agrees Wright. Typically they offer longer tread wear and a smoother ride.

These characteristics make them an obvious choice for transport equipment, such as articulated dump trucks and rigid-frame haul trucks. "Transport machines were probably the first to use radials," says Bruce Besancon, key account manager, Earthmover Group/Michelin North America. "In most cases, those were the ones with the highest rate of tire usage. They could factor in the savings they were achieving out of the radials quicker than those on other products."

"Construction trucks operate at high speeds and carry tremendous loads," says Mills. "Radials really show their advantages here. Better traction, less heat and less rolling resistance all lead to better performance, increased productivity and improved operator comfort."

Work tools such as wheel loaders and scrapers are now moving toward radials. "The work tool tires have taken longer to switch over," says Wright. "In Europe, loaders are 100 percent on radials due to longer tread wear and ultimately operator comfort. In North America, the changeover has been much slower, I think due to the fact that the stability is not the same."

Puncture & cut resistance

"Radials are about 80 percent more resistant to cuts and penetrations in the tread area," says Mills. This is due to differences in construction between radial and bias-ply tires.

A bias-ply tire is made of layers of rubber-coated, criss-crossed plies of fabric placed at angles of approximately 30 degrees. Nylon is the commonly used fabric. The tire is constructed to form a single working unit.

A radial tire is constructed in two parts. The casing has one layer of rubber-coated steel cables that arc from one bead to the other. Then several rubber-coated steel plies make up steel belts that are placed under the tread to stabilize the crown. These belts resist cuts and punctures.

"You have to cut through a number of steel belts to cut all the way through the tire in the tread area, where you are going through fabric on a bias-ply tire," says Wright.

This often results in less downtime due to punctures. "It's not uncommon to see a reduction in flats by 80 percent," claims Bennett. "If you put a pencil to it and just said you want to reduce your flats 20 percent, it would more than pay for the tire."

When cuts do occur, the radial tires are often more repairable. "If the radial tire is damaged, it only damages a very small portion of the tire," says Besancon. "If a bias-ply tire is cut in the sidewall, it affects 25 to 35 percent of the overall structure of that tire."