[RH77]

Well, I'd better comment since I brought-up the whole 55-deal...

My car also gets better FE at 65 than 55 in hilly terrain (which is where I drive). Aero's mention of "Momentum Driving" is spot-on.

Let it be known that I'm not advocating a blanket 55-limit. The core of my argument is that our current speed limits are often beyond that of a vehicle's optimum load, from an aerodynamic perspective. The "Wall of Air" theory. The best example in recent history was the national 55-limit.

I just drove 500 miles in an '09 Chevy Malibu 4-banger, 4-speed. With a constant tailwind of about 10-15 MPH, I got about 31 MPG at 70 MPH (speed limit). I sped up to 75 to outrun a thunderstorm, and the mileage average during that segment was ~28 MPG. In construction zones, 55 MPH yielded ~33 MPG (smaller subset of data). So an argument could be made that 65 would be a good compromise. In the many cars that I've driven, the difference between 65 and 70 had a dramatic impact on FE. 75 even moreso.

The stigma that's attached to "55" will not soon be forgotten. The average person tends to speed. Life is getting faster -- all that mess. Lowering the limit would have a backlash, yes. Just 3 years ago, I remember seeing limits of 75 cropping up and simply enjoyed the speed.

So, what are we to do? Many trucking companies have a 61 mph governor on their tractors. A statistician/accountant somewhere figured the time and money equation. Unfortunately, owner/operators are stuck with per-load requirements to "make the mortgage" on their rigs.

But the "fell asleep because it was too slow" argument doesn't sit right. Driving at 80 mph sleepy, seems to be the same as 55 to me. What about railroad engineers? They don't even have a steering wheel and tend to stay awake at speeds of 45 mph all day and night.

Now for passenger vehicles. Again what to do? Since we essentially have a mixed bag of BSFC maps and Cd's out there on the road, wouldn't it make sense to cap limits at 65?

So, am I foolish for driving a company-paid vehicle at the limit for many hours? I'm a salaried employee, so I'm not making any more money. I could have set the cruise for my old traditional "6-over" and got to the hotel early, so I could plop my arse, watch TV, and post on EM. Honestly, I would rather use fewer gallons of fuel in the process, like Tas.

RH77