Tires have a large impact on vehicles' fuel economy. At an event in New York City last week, executives at Michelin tire said that after discounting engine and other losses, tire rolling resistance accounts for about 20 percent of the energy needed to power a car. Overall, Michelin figures that tires account for about 3 to 5 percent of the nation's CO2 emissions and about 9 percent of U.S. oil consumption.

In a country burning nearly 4 billion barrels of gasoline and diesel fuel per year for transportation, as the United States is, that's a lot of fuel going to turning tires. Doing the basic math, 3 percent of 4 billion barrels is about 120 million barrels a year. Rolling resistance varies with tire wear, condition, alignment, load, speed, inflation pressure, and road texture, so exact calculations are difficult to come by.

Jim Micali, president of Michelin North America, says that the company's next-generation Energy Saver tire can cut rolling resistance by a further 20 percent over its current line of low-rolling-resistance tires. Michelin expects that a 50-percent reduction in resistance is possible in the next 10 to 15 years. A 20-percent reduction in rolling resistance would be equivalent to a 3-percent savings in fuel consumption for drivers.

At the same time, the company turned on a Times Square billboard (in conjunction with similar ones in Berlin, Paris, and Shanghai) to track how many gallons of fuel the company says drivers have saved worldwide by using its current Energy series of high-mileage tires, compared with the industry average for rolling resistance. The number started out at 2,380,056,909 gallons, and it is increasing by 11.6 gallons per second. (See the latest numbers in the online green meter.)

In our recent new-car testing, we have seen that cars and trucks with low-rolling-resistance original equipment tires sometimes sacrifice grip. Some tire suppliers say some auto manufacturers put higher priority on low-rolling resistance over other performance criteria. In testing aftermarket all-weather tires, we have found that it's possible to get a very good performing tire with low-rolling resistance compared to other tire replacement tires. And Michelin says its upcoming line of low-rolling-resistance tires will save energy without shortening tread life or reducing grip.

The state of California is working on developing a rating for tire rolling resistance, which it plans to require tiremakers to print on the tire sidewalls starting in 2009. Meanwhile, to help consumers choose the appropriate replacement tires, the California Energy Commission is developing a complete database of all replacement tires marketed in the state. The database should be available in 2007 or 2008. Today, tires are required to have ratings printed on the sidewall for traction, tread life, and temperature.

Consumer Reports supports increasing consumer awareness of tire efficiency, which is why we test and provide rolling resistance ratings in our tire performance studies. Rolling resistance is one of many key performance attributes Consumer Reports tests as part of its tire ratings.

Giant billboards like the one in Times Square may help raise awareness of the problem to a small degree, although it omits savings by any other tiremakers' products. In the effort to be perceived as a "green" company, it is hard to miss the irony of using megawatts of electricity to deliver the message. Still, if the savings are that big for one brand, there are clearly more gallons to be saved across all brands that offer low-rolling resistance tires. CR recommends that consumers consider a lower rolling resistance tire as a tie-breaker between two or more models, but don't sacrifice the safety of good grip for low rolling resistance.   

--Eric Evarts

updated 7/16