The Department of Energy says 5 to 15% of fuel economy is used for overcoming rolling resistance. This means your existing car could benefit by 5% or more from low rolling resistance tires. The trick here is that this tire type is almost never produced for your basic or larger vehicles. There seems to be a production focus for hybrids and electrics for this type of tire.

Next, the independent study information: Tire Rack is a group that does tire performance testing. This group has studied various LRR tires against a control tire for a standardized comparison. Note that they do not have separate measurements for city vs highway driving.

Matt Edmonds, a Tire Rack vice president, 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.

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.

The way I see it, we can have the most impact right now by keeping our tires properly inflated. Make it part of your gas station pit-stop.

There is a great chart with comparisons of brands on the related link.