Pavement researchers at the Virginia Tech Transportation Institute (VTTI) are examining the use of cost-effective single wide-base tires in place of dual tires on big rigs. Sponsored by a grant from the Michelin Americas Research and Development Corporation, the research uses field-test data and computer simulation to address the concerns of U.S. pavement engineers that wide-base tires may cause a significant increase in pavement damage on roadways. Pavement deterioration presents serious economic, safety, and traffic concerns. The American Society of Civil Engineers estimates that $1.3 trillion is needed to repair the nation's infrastructure over the next five years.

"People were really interested in our results," said Dr. Imad Al-Qadi, Charles E. Via, Jr. Professor of Civil and Environmental Engineering at Virginia Tech and leader of VTTI's Roadway Infrastructure Group. Wide-base tires offer many economic and safety benefits for the trucking and transportation industries, including improved fuel consumption, saving as much as 1000 gallons of fuel per year in a typical tractor-trailer; increased pay load; increased driver comfort; improved handling and braking; lessened repairs; and reduced tire costs.

Michelin first approached VTTI's Roadway Infrastructure Group in 2001 to measure the pavement damage caused by wide-base and dual tires. Researchers tested a new wide-base tire developed by Michelin to lessen pavement damage. Previous generations of wide-base tires caused concerns because of their size, shape, and high pressure levels. The new tire offers a wider, flatter footprint; uses a stronger, crown-belt tire wall; and operates at the same tire pressure as dual tires.

Pavement researchers at VTTI tested tires under different loading and environmental conditions and at different speeds and tire pressures to fully understand the pavement's response to both kinds of tires. The tests were performed on the Virginia Department of Transportation's state-of-the-art Smart Road, which includes 12 different pavement test sections designed and instrumented by the Roadway Infrastructure Group. These sections contain embedded sensors to measure strains, stresses, frost depth, moisture, and temperature.

The tests showed that the wide-base tires induced approximately the same damage as the equivalent dual tires. In addition, researchers determined that the largest contributing factor to pavement damage is the axle load, or weight carried by the truck's axles, rather than the tire pressure, as was originally believed. Tire pressure was only found to be a factor at shallow depths.

Based on these results, VTTI received another grant from Michelin to develop computer-simulated models that can determine the effects of wide-base tires on any roadway in the world. Starting in Jan. 2003, researchers began using a computer-based technique called Finite Element Analysis (FEA) to create simulated pavement models that allow them to predict pavement response and damage from moving tires.

These models provide similar pavement responses to those measured during testing on the Smart Road; however, researchers can "change the effect of the environment and loading as well as the properties of the pavement system in order to look at any different loading and materials used, " said Al-Qadi. The models are significant because they are based on real-world, rather than hypothetical, information. "People usually develop a theory and then test. We wanted to see first if this would work before we develop the model," said Al-Qadi.

VTTI's research has increased national and international interest in wide-base tires, and many engineers and trucking professionals are considering making the switch. Al-Qadi was invited to discuss the results of his group's study last November at the Canadian Transportation and Equipment Association Annual Meeting & Manufacturers Conference in Toronto. "Canada is currently considering using the single wide tire," he said.

For more information about this project, please contact Dr. Imad Al-Qadi at (540)231-5262 or alqadi@vt.edu.

Written by Ennis McCrery

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