http://online.wsj.com/article/SB1197...googlenews_wsj

sample quote:

As much as 20% of the energy needed to operate a car is tire-related,
according to some industry estimates.
The lower a tire's rolling resistance, the less energy the car consumes.

A study last year by the National Academy of Sciences in the U.S. estimated that as many as two billion gallons of gasoline and diesel fuel could be saved each year in the U.S. by reducing the average rolling resistance of automobile tires by 10%.

In Europe, adding low-rolling-resistance tires to cars drives up their production costs by about $30 to $45, per vehicle, based on estimates by Credit Suisse Group.

For manufacturers, an easy way to cut a tire's rolling resistance is to reduce the thickness of its tread. The problem, some industry officials said, is that reducing a tire's rolling resistance too much can weaken its traction or shorten the tire's life span.

Germany's Continental AG said its tests indicate that tires designed primarily with low-rolling resistance in mind tend to have longer stopping distances on wet surfaces. The National Academy of Sciences study, however, reported that the safety consequences of reducing tire rolling resistance "are probably undetectable," and that a 10% reduction is
"feasible and attainable within a decade"
through new tire technologies and improved designs.