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Recently bought a 2009 Prius w/ 50K miles. It has Yokohama DB super E tires, which I keep at 40 PSI front, and 38 rear. Using Mobile 1 5W-30. I use it for a long daily commute, there are only a few gentle hills along the way. So almost all the mileage is at hwy speed....and I keep the cruse set at 65mph. The MFD is showing average MPG is 44.5 MPG. But I have heard of people getting 50MPG and over. How are they doing that? I was really expecting to get around 48-50 mpg. And I was expecting the MPG to beat Jetta TDI!
I heard of one Prius owner with the same tires, he is runnning his at 4PSI higher (44/42), and says that the tread wear is still even. You would think it would perhaps wear in the center more than towards the outside. So I was thinking of trying a little bit higher pressure myself. Ideas? I don't really know why Toyota wants the two rear tires to run 2PSI lower than the front. Is there really any point or advantage to that?
One other question: I always used M1 5W-30 in my now retired commute car, an 04 Corolla, and added a little Lucas oil stabilizer. Can I continue to use a quality oil stabilizer like this, or is it not a good idea?
 

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We have a 2002 Prius and have run 44/42 psi in several sets of Michelin tires. They wear evenly, but must be rotated every 5-10,000 miles.

The best highway economy is between 45 and 55 mph, assuming traffic allows that speed. Wind resistance seriously affects mileage; and the faster one drives, the lower the mileage. If you have a lead foot, don't expect good economy.

Use cruise control as much as possible, because this allows the hybrid computer to optimize the ICE and electric motor use for best economy.

In town, the best mileage is when the weather is nice, and you can drive with the windows down, at 42 mph or slower. Above 42 mph, the ICE runs more often. At 42 and below, the computer favors the electric motor.

Accelerate from traffic lights at near full-throttle to reach cruise speed ASAP, to reduce ICE use (the longer duration ICE runs, the more gas is burned). At about 30-35 mph, switch to cruise and use cruise control to bump speed up gradually, 1 mph at a time, to 41-42 mph.

Also, figure out the speed that traffic lights are synchronized at and try to hit all lights GREEN, without stopping. Anticipate RED lights and use cruise control to bump down 1 mph at a time, starting about 1/2 mile from intersections. Watch when the computer switches ICE to ON, and bump down on cruise control to turn ICE to OFF, and maximize coasting time. This will allow you you to maintain reasonable speed over long distances.

If you plan right, you can either roll through all lights on GREEN (even if you have to slow significantly), or roll to a stop without using the brakes. By the way, this will really annoy other drivers. However, smart ones will figure out what you are doing and follow you. When gas was over $4/gallon a few years ago, I had a lot of commuters (large cars, minivans and pickups) that recognized our Prius at the same time everyday, that started following me, instead of passing. Besides, most of the cars that pass you will be stopped, waiting for you at the next RED light; and if you time it correctly, you'll roll right through, and leave them as you accelerate hard when the light turns GREEN.

By the way, by accelerating hard off of traffic lights, this will put you ahead of the traffic, so that when you switch to cruise control and start bumping up 1 mph at a time, you'll be ahead of the pack. About the time you reach 41-42 mph, they'll just be catching up to you. This will reduce the impact of this odd driving technique on other drivers.

By following the above techniques, I have achieved 52-56 mpg on the same commuting route, in the spring and fall. During the winter and summer, when the ICE runs more frequently for heating and air conditioning, I usually get about 42-46 mpg on this same route.
 
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