Will low rolling resistance tires save enough gas to justify their cost?

Want to save gas? Well, you could buy a Toyota Prius and get 50 miles per gallon, or you could just swap the tires on your current clunker and get close to five percent better fuel economy. The key is low-rolling-resistance (LRR) tires, which are standard equipment on hybrid and battery electric cars, but rarely make it onto the average cars most of us drive. The Department of Energy says five to 15% of fuel economy is used for overcoming rolling resistance.

Of course, it's not as simple as just switching tires and saving money. The extra cost of LRRs (some run as high as $170 each) means that you'll probably come about even in spending. But your greenhouse gas and local pollution emissions will be better, and that's the main reason people buy cars like the Prius in the first place. Save a gallon of gas, and you also prevent 20 pounds of carbon dioxide from entering the atmosphere. The gas savings are secondary.

The Tire Rack, a big direct-response sales company, recently ran seven different LRRs (three from Goodyear, two from Michelin, and also entries from Bridgestone and Yokohama) through track tests on a small fleet of Priuses, using a set of Goodyear Integrity all-season radials as the base comparison. The results were interesting.

The best performer was the Michelin Energy Saver A/S, which delivered 53.8 mpg in a Prius, meaning a 4.74% improvement. The Bridgestone Ecopia EP100 was next, with 53.5 mpg and a 4.12%. On the other hand, both the Michelin HydroEdge with Green X and the Goodyear Assurance ComforTred (terrible name) actually did worse (down .59 and 2.64% respectively) than the control tires.

Company claims do not always jibe with Tire Rack's findings. Goodyear claims a four percent improvement in highway fuel economy (and 27% less rolling resistance) with its Assurance Fuel Max, the tire that will be on the Chevy Volt, but Tire Rack recorded only a .37% improvement in the testing. A key issue is that the Tire Rack didn't differentiate between city and highway driving, so that could be one explanation.

Matt Edmonds, a Tire Rack vice president, said in an interview that tiremakers have made major strides in producing eco-tires that perform well under both dry and wet conditions. Asked about noise -- a frequent complaint about LRRs -- he said, "We did notice that there was more road noise than usual, but we aren't that familiar with the Toyota Prius so it may have been the car itself."

Some have complained that LRRs hurt hybrid braking distance, but the industry addresses that, too.

Edmonds said that almost none of the tires would save money for the people who bought them. In the best case, you'd save about $52.50 per year if you drove 15,000 miles a year. But carmakers will inevitably be drawn to these tires as they try to meet the new 35.5 mpg federal Corporate Average Fuel Economy (CAFE) standard for 2016.

In effect, all original-equipment tires are eco-tires because carmakers really care about their fuel economy and push suppliers to help with the mileage figures. LRR's should last well, by the way. The Goodyear Fuel Max, for instance, has a 65,000-mile tread wear limited warranty.

Incidentally, you could do a lot to help your fuel economy if you just properly inflate your tires. A Bridgestone study found that 93.5% of European cars have under-inflated tires, wasting 2.14 billion gallons of fuel a year. Americans are definitely no better. And forget about inflating your tires with nitrogen. It sounds great, but Terry Jackson of Bankrate.com points out that nitrogen already accounts for 78% of the air in your tires. Pure nitrogen doesn't make enough of a difference to be worth the effort.

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