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Jesus I got 34 mpg!!

2K views 10 replies 10 participants last post by  Keepittrill 
#1 ·
Today for about 100 miles I was averaging 34 mpg!! My engine was already warm before I started the measuring. I was driving slow, 65 to 70 miles per hour due to some traffic on the highway. I notice as soon as I started to drive faster than 70 mph, the averaging begin to drop. It seems that the highway MPG is affected significantly by your highway speed. No wonder during my vegas/grand canyon trip I was only averaging 23 mpg, because I was driving 90 to 100 mph.

My car is 28i, has 17K miles as today.
 
#3 ·
26 has been the best we've had in terms of highway MPG, and that was in the 80 mph range and ECO Pro mode. Around town we can barely pull 20 mpg in ours x28i. Pretty disappointed.
 
#8 ·
Its actually a lot worse than that.

The so called "Force of Drag", Fd, is indeed proportional to the square of the velocity. However, the power required to overcome the aerodynamic drag is proportional to the cube of the velocity. Therefore it actually takes nine times as much energy to say increase from 40 mph to 80 mph.

See the following link:

http://en.wikipedia.org/wiki/Drag_(physics)

The following quote is from this link.

"Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power."
 
#9 ·
I picked up my 2.8i in April and have put just over 5k miles in a mixture of highway and suburban driving. My consumption via the computer seldom goes below 23 and averages well over 24 in my mixed driving. "Real" miles divided by gallons is usually about 3/4 mpg less than the computer.

I recently had a single day 300 mile interstate round trip with about 15 miles of pure urban driving in the middle. Sustained 75 mph on the highway, but "gentle" throttle to hold hills and move in and out of lanes. My "real" mpg was just shy of 30 and the computer showed over 31.

Am I happy? You bet!




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