mpg sucks on highway

Cruise at 70, I get about 19 mpg.

Cruise at 55, I get 24.

 

16-17 hwy. I got the same with stock tires, 20's, and the 18's I have now. They were all the same height and according to the GPS my speedo is dead on.

 

With my ScanGauge and CC set at 55, it reads 23-24mpg.

With CC set at 70, my ScanGauge reads anywhere from 17-21, depending on road and weather conditions. One of the reason I hate headwinds; mpg drops to 16-17.

Moral of the story? Slow down.

 

Got 25 mpg yesterday on a 400km trip, most of whnich was driven at 110kph

 

Hey, OP didn't say anything at all about stopping... just going...

 

Wow, that's nice... Imperial gallons?

 

http://upload.wikimedia.org/wikipedia/commons/a/a9/Fuel_economy_vs_speed_1997.png

Here is a graph that shows how, no matter what you drive, that you will start to lose mpg after a certain point. This point is determined a lot by wind drag, and the "boxier" your vehicle the more drag it will encounter. Note that the best mpg for the pickup and SUV is around 45 mph.

Edit: I wonder if those "wiggles" in the graphs for for some of the vehicles have to do with automatic transmission shift points.