In case you missed the latest from the Click and Clack brothers of Car Talk;
They answered questions from a Prius owner who was told the only place he could get
the proper 'low resistance' tires for his car was the dealer. And, simply, that ain't true no more.
They said tests were done and the info is available at: http://www.tirerack.com/
There are a number of tires that give better performance
than the original factory installed rubber.
In the search box, enter: "When Round and Black Becomes Lean and Green."