I can either file this under "the early bird gets the worm" or "wait long enough and someone else will do it for you."
I intended to write a well-rounded, informed article about low resistance tires inspired by my post about the physics of MPG. Green Seal, however, beat me to the punch in a big way. They wrote a great PDF, found here.
I would just direct you there but then you won't read it and, honestly, neither will I so here's a summary.
is not a measure of a tire’s traction or “grip” on the road surface, but rather simply indicates how easily a tire rolls down
the road, minimizing the energy wasted as heat between the tire and the road, within the tire sidewall itself, and between the tire and the rim.
This means a low resistance tire is not, absolutely, going to grip less or function poorly. Literally rolling down the street requires no grip... the less the better, in fact.
Rolling resistance has traditionally been measured through an official Society of Automotive Engineers (SAE) test procedure known as J1269. It measures the force required to roll a tire against a
dynamometer at a fixed speed of 50 miles per hour.
Good information to know...
The highest and lowest rolling resistance tires we tested differed in efficiency by 60%, indicating that tire choice can have a bigger impact on fuel economy than most people realize. Rolling resistance
differences of 20 to 30% are not uncommon among tires of an otherwise similar size, type, and level of performance. This means an individual vehicle could save up
to 6% of its gasoline use if it were fitted with very efficient tires,
That's a solid improvement.
Keep in mind, you won't see these articles (or myself) urging people to run out and ditch their tires for low-resistance ones. The point is, when the time comes to replace them, do it sooner rather than later and do it in a way that saves you money and saves some oil.
This report does address the life cycle of a tire as well:
Thus, a tire’s rolling resistance is likely to be a larger factor in its life-cycle environmental impact than its composition, longevity, or ultimate fate, though those factors merit consideration
So, if you're getting close, get 'em replaced. With what? Try these:
On a personal note: My rear tires are "cupped" according to my mechanic and are asking to be replaced soon. I am still recording my MPG and intend to see what kind of real-life increases I'll see. I'll post a MPG chart soon!