Speed, Fuel Ecomony and More

This labor day I traveled from Colorado to Iowa and was frustrated by the fact that the miles per gallon that I was getting was not near where I was when I traveled from Colorado to Massachusetts. It was a difference of 5 miles to the gallon - that is huge in a big car like a Crown Victoria. I had gone from 24mpg to 19mpg in the space of 12 months and I had been keeping up on the service of my car. Not only that, I had the car checked out before I left.

Around town I usually get 20/21mpg and the lower number on the highway was a shock.. until I realized one very small thing, and it is the size of a foot. This trip was 90% driven by my roommate and her speed ranged from 75/85mph. However, when we drove to Massachusetts last year, I drove about half of the time and when I drove I rarely drove over 60 so it averaged about 65/70 between the both of us.

That didn't seem like a big difference to me but it was enough for me to notice the 5mpg difference in our trip. And recently Consumer Reports tested speed vs. fuel economy found that there is a noticeable difference based on the speed that you drive.

The car's trunk and back seat were filled when driving to the east coast; but pretty empty going two states over and the tires were up to snuff on both road trips, the only difference that I can tell is the speed traveled and that the Crown Vic was a year older.

However, when it came to driving to the east coast we had no rush, where as the trip back from Iowa meant a few more hours of sleep before work the next day, so speed was of the essense. Some might say the time saved would be worth the loss of the miles per gallon, I just didn't realize the difference would be that noticeable.  Personally I'm fine with any speed, but not to sacrifice safety in the process, and that has to be gauged by the person driving and the surroundings.

Have you found a difference in your mpg depending on speed, lightness of the car, tire pressure, etc?