I was just out on a major highway for a long period of time in my car. This is really the first time. I started doing a little test and I'm not sure if I proved anything or not. This of course is totally un-scientific.

When I got on relatively flat, straight stretches, I would pick a speed, set the cruise then zero out the mileage calculator. After at least a mile I recorded the results. Here is what I got (bear with the weird numbers I'm in Canada so everything is converted from kms and "liters per hundred kms")

50 miles per hour - 63.6 mpg (US gallon)
56 miles per hour - 51.1
62 miles per hour - 45.2
75 miles per hour - 42.8
81 miles per hour - 32.7

So this is with the car warmed up and already at that speed. I was surprised at the drop between 50 and 56 miles per hour although weren't we always told that the optimal speed to drive a car is about 50 miles per hour? Also, once you hit about 80-81 miles per hour the eco light won't come on anymore.

Comments?

Cheers

Gregg