Have a look at the list of U.S. EPA SmartWay approved low-rolling-resistance, fuel-efficient tires and you'll notice there are no retreads on the list.

They are absent because of the difficulty in quantifying the relative fuel efficiency of a two-part system. Like tractor and trailer braking systems, casing and treads are designed to work together, but a host of variables in both cases makes objective measurements a challenge. Of late, there has been a lot of interest in getting retreaded tires onto the SmartWay list. We should see them there soon, possibly as early as 2011.

Historically, tire manufacturers and retreaders individually provided EPA with data on their retreads, but they often used different test methods. Left to sort the data out for itself, EPA concluded it needed more consistency across the tests and the results in order to make a decision. So, a committee of tire manufacturers from within the Rubber Manufacturers Association was formed and charged with developing a single test method and a reporting system to help EPA sort out the multitude of treads and casings on the market that could conceivably one day become a single retreaded tire.

Part of the challenge has been defining the "retreaded tire" within the SmartWay context. Is it the casing you measure, or the tread? Kyle Jensen, manager of industry and government relations at Bridgestone Bandag Tire Solutions, says while measuring the rolling resistance contribution of the tread alone is difficult enough, measuring casings is equally complex.

"Each retreaded tire is a unique product because of the history of the casing," he says. "Given its age, previous applications, etc., achieving rolling resistance values for each casing would not be easy."

Without a precise definition of a retreaded tire in this context, the default position is that a SmartWay casing should be the basis for a SmartWay retread. That, however, could allow any tread - even a deep lug tread - to be used on a SmartWay casing, and thus be considered a SmartWay retread. That's clearly not the desired outcome.

Typically, the casing accounts for less than half of the tire's efficiency, and there generally isn't a great deal of difference across casing brands of similar design and application. The tread, most agree, has a greater effect on rolling resistance.

"Most of the casing is steel. You can't do much with that," says Roger Stansbie, director of radial truck tire technology development at Continental Tire. "It's the rubber surrounding the steel where you can fine-tune some minor improvements. When we develop a low-rolling-resistance tire, what we're doing is refining the tread compound and the tread design."

The RMA committee is working on the premise that if you de-emphasize the role of the casing - after establishing a rolling resistance standard for applicable casings - and work toward an objective rolling resistance measurement for tread designs and compounds, you'd have a more objective way of determining the fuel efficiency of a retreaded tire.

Larry Tucker, marketing manager for commercial tires at Goodyear, is a member of the RMA committee examining this situation. He says EPA is looking for a way to define a tire that meets its greenhouse gas reduction objectives, and industry is stepping up the plate to help.

"We are going to decide on which test method, what wheel position, and what testing criteria is needed to provide accurate data on rolling resistance by wheel position, by tread design, and by casing," he says. "It will be our responsibility to give the EPA the data it needs to make informed decisions in setting the target values."

Assuming the committee is successful, the next step would be to develop a common mark manufacturers can use to certify their retreads to SmartWay standards. "We have to identify a 'retreaded tire,' which includes the casing and the tread. The marking will have to go on the face or the shoulder of the tread," Tucker says.

"Once we have collected sufficient data on retread tires, our intention is to analyze the data to better understand the range of rolling resistance for retread tires, the effect of the casing on retread tire rolling resistance, and even the effect of the tire retread process itself on retread tire rolling resistance," says Dave Ryan, spokesman for SmartWay. "We need to understand these factors before we can establish retread tire criteria for SmartWay."

If the RMA committee is successful in establishing a measuring system for tire treads that opens the doors to using retreaded tires on any casing – not just SmartWay casings – fleets facing a looming deadline in California will be heaving a huge sigh of relief.

To qualify under the California Air Resources Board rules right now, only SmartWay-certified casings can be used for approved retreaded tires, says Michelin's Baldwin. There just are not enough casings from SmartWay-approved tires in the pipeline yet. If fleets have to buy new SmartWay tires in order to get into California, the budget impact will be huge.

"Our challenge as tire manufacturers, and the retread subcommittee, is to get the data EPA needs in a very timely fashion to they can make a decision in a very timely manner," notes Tucker.