ConsumerReports Blog 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 trillion 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 trillion barrels is about 120 billion 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. I wonder what kind of crazy milage we could pull out of the current Prius/Civic with tires that were rated at 50-percent less rolling resistance!
I am currently collecting data using my 2004 Prius on MPG vs tires. I ran the original Goodyear integrity tires for 44.5k miles (almost two years) and Michelin MXV4+ "Energy Saving" tires for 55k miles (two years, no longer available in our size). My data showed that the MXV4s matched the GYs in warm weather and did better than the GYs in cold weather (the use of OrganoSilicates in the rubber compound helps to keep the tire flexible in cold weather) managing to produce a 0.6 MPG overall improvement. I am now running Nokian WR tires. They appear to have increased my car's efficiency by about 2 MPG (an additional 4% savings - a surprisingly good result), but since they have only gone 1.5k miles, I will have to wait a few more months to get valid data. Nokian appears to be ahead of Michelin to date in producing LRR tires. I have a spreadsheet that tracks and analyzes this data which can be found in other discussion groups. JeffD
<div class='quotetop'>QUOTE(F8L @ Nov 19 2007, 12:42 AM) [snapback]541483[/snapback]</div> Well, using the 3% saving for 20% reduction in rolling resistance metric, a 50% reduction in rolling resistance should get to 7%-ish saving. At a baseline of 50 mpg combined, 7% works out to 3.5 mpg improvement. Which isn't chump change. I think that this is an example of a number of participants working together to improve the efficiency of the car. It is possible to achieve a corporate average of 50 mpg; it just requires motivated participants that are willing to see how far they can exercise their creativity.
If this new tire makes that much difference in comparison to Michelin's current LRR tire, how much of an improvement is it compared to their regular tires, or tires from other manufactures? This is where an Energy Star rating system for tires would come in handy. And if governments would further increase CAFE and fuel efficiency standards for all vehicles, auto manufactures would be demanding tire makers supply better OEM LRR tires.
