Tire manufacturers have begun to make serious efforts towards making fossil fueled vehicles more efficient by designing tires with lower rolling resistance. By reducing the amount of energy required to start and keep a tire rolling, the car becomes less expensive to run long term and reduces its impact on the environment by reducing carbon emissions.
Last year, we did an enjoyable test with the Toyota Prius, and then, this past week, we tested the newest entries in the Low Rolling Resistance (LRR) category on our normal fleet of BMW 3 Series. We are still finalizing the results from the most recent test, but I can tell you that the differences in fuel mileage were not huge. However, when the difference is factored in over the life of the tire, the differences can be significant.
You have to be careful with LRR tires since they can have low traction levels when stopping in the wet. Based on last week's experience and last year's testing results, here are a few LRR tires that I suggest:

The Continental ProContact with EcoPlus Technology: I first drove a prelaunch version of this tire at Continental's test facility in Texas and was immediately struck with the ease at which it handled wet stopping tests. It is very comfortable and should wear well with proper rotation and care (which will be easy to achieve since it is a normal symmetric tire).

The Michelin Energy Saver A/S: Performed well in the wet portion of our testing last year and was a pleasure to drive. The tire had great road manners and ride quality.
There are other good LRR tires and most of them provide a good balance of handling, ride quality and wet traction. However, these two are great options in a tire category that will continue to grow.
Last year, we did an enjoyable test with the Toyota Prius, and then, this past week, we tested the newest entries in the Low Rolling Resistance (LRR) category on our normal fleet of BMW 3 Series. We are still finalizing the results from the most recent test, but I can tell you that the differences in fuel mileage were not huge. However, when the difference is factored in over the life of the tire, the differences can be significant.
You have to be careful with LRR tires since they can have low traction levels when stopping in the wet. Based on last week's experience and last year's testing results, here are a few LRR tires that I suggest:

The Continental ProContact with EcoPlus Technology: I first drove a prelaunch version of this tire at Continental's test facility in Texas and was immediately struck with the ease at which it handled wet stopping tests. It is very comfortable and should wear well with proper rotation and care (which will be easy to achieve since it is a normal symmetric tire).
The Michelin Energy Saver A/S: Performed well in the wet portion of our testing last year and was a pleasure to drive. The tire had great road manners and ride quality.
There are other good LRR tires and most of them provide a good balance of handling, ride quality and wet traction. However, these two are great options in a tire category that will continue to grow.

Unfortunately, if you are going to change tires on your vehicle, especially to those which sound like they are vastly different that what you have on the other axle of the vehicle, you want to change all four at once. To do otherwise could cause terrible handling results, and would not be recommended at all.
Best!
If a 15,000 mile-a-year driver’s tire choice could influence their vehicle’s fuel economy by just 4% (i.e., 30.0 mpg to 31.2 mpg) they could potentially reduce fuel costs by $80/year.
Tire Rack began measuring and reporting the influence tires have on vehicle fuel economy during the Toyota Prius Hybrid tire test we conducted in 2009. We go to great lengths to fairly measure and report fuel economy on all of our tests today.
Our goal is to show the relative differences between replacement tires that are often being considered by consumers. However, in addition to measuring fuel economy, we also evaluate on-road manners along with on-track capabilities in wet and dry conditions.
Tire Rack recommends drivers consider dry and wet performance first and look at the tire’s influence on fuel efficiency as a tie-breaker. Our hope is to report on something of interest to many drivers, not push it.