Low tire pressure = low mileage

I have 6600 miles on my Prius. When I first go my prius I increased my tire pressure to 40 psi. At 5000 miles I got an oil change and my checkup. Took a road trip of 400 miles and got 53-54 mpg.
Just before my fill up at 5500 I put a screw through my front passenger tire. Toyota fixed the tire for $10 and I was on my way.

The last two tanks of gas I have only gotten 45 mpg and was ready to take the Prius back into Toyota and ask them to fix whatever they did to the car.. To make a long story short I decided to check the tire pressure on all the tires again. Three of the tires were at 40 psi and the one Toyota fixed was at 35 psi. I inflated the one tire to 40 psi and not I'm right back where I was on the mileage. 52-53 mpg.

It's really hard to believe that 5 PSI on a front tire dropped my mileage from 52 to 45 mpg. That a 14% drop in mileage due to 5 psi difference in one tire. WOW!!!

Moral of this story, make sure all your tires PSI match.

 

I do agree with you on your points. My driving pattern did not change the last two tanks. The only reason I can think of in seeing a major difference in mileage is the transmission had to work harder to turn the tires with such an difference in tire pressure.

I don't have the average distance but as I said before our driving pattern didn't change. We live 3 miles from downtown and it's all down hill one way. Easy to average 99.9 on the way down and by they time you return home the average is usually 53 or 54. I live 13 miles from work and I usually average 54 or 55 going to work and back. It is not unusual for us to drive 25-30 miles one way and back and see an average of 55. Now mind you that is what the prius says and so far the prius has been showing 2 mpg better than I actually get.

I don't have the exact number but when I filled up I genrally saw 50-55 mpg. Most of the tanks were right around 52.

 

I should also add I generally reset trip A on my car every time I leave the driveway and monitor my mileage while driving. It is really enjoyable to constantly try and improve my MPG.

PS: This drives my wife nuts so when she is in the car I don't do 50-55 mph on the hwy I do 60-65. I also speed up to 65 if traffic is heavy to not upset other drivers (had to throw that disclaimer in).