The mail bag is getting full and it would be the polite thing to do to answer the questions and make room for more. Santa Skip wrote the following after I used the term Tommy Knocker:
“I spent my younger years exploring the ghost towns of CO, to me a tommyknocker was a little elf who lived down in the mine, if he liked you he would show you where the gold, (was) if he didn’t he would cause all kind of problems.”
One of the neat things about traveling is that you get to learn that an expression that you grew up with have different meanings regionally. But this is a new meaning of Tommy Knocker to me.
Chuck wrote the following after my comments on driving at 55 miles per hour:
“I’m posting this as a reality check. I’m getting better MPG at 68-72 mph (2200 rpm) than at 55 mph. I drive a F250 with a V10. With or without the 5th wheel trailer I get better mileage at a higher speed and higher rpm. At my last fill up I got 10.8 mpg. I traveled 107 miles with the 5th wheel trailer and 190 miles without the trailer. In the past if I drove at 55 I would get around 8 to 9 mpg. Has anyone else seen this type of mpg driving faster instead of slower?”
Under real world conditions it is almost impossible to get accurate fuel economy numbers. Back in the dark ages, about 1980 something, the EPA was in the process of certifying fuel savings devices. They invited a group of automotive writers to a test drive to provide the EPA with numbers of fuel economy improvement of the new Volkswagen E Shift light system. It was a computer controlled device that would turn a light on on the dash that would signal the driver when to up shift for best economy. The route was from the tip of Long Island to Newport, Rhode Island. Lots of rolling hills.
VW teamed up the drivers and it happened that Dan Holt, then a writer/editor with the Society of Automotive Engineers publication, and I drew the duty as partners. Now not to say that we were heavy, but between the two of us we exceeded the load carrying capacity of the car, not counting our luggage or our camera gear. Now as every one knows writers have imagination. Dan and I being both engineers decided that we would show some real fuel economy, and here is how we did it.
The first thing that we did was to eliminate rolling resistance. We stopped and pumped the tires up to 80 PSI. The car rode like it had Freddy Flintstone Hard Rock tires. Then we applied some simple junior high school physics. Gravity. We figured with our combined weight, the weight of the car, and gravity, that we could use the engine on down hill runs to get the speed up, and then coast up the next hill. Foot to the floor in high gear going down hill, put the tranny in neutral and shut the engine off for the uphill coast. In several instances on the run we were able to leave the engine off for several hills as well as seeing the tach hit red line in high gear.
VW controlled the record keeping of fuel in each car with a burette attached to the front bumper and at each fuel stop they measured fuel used and filled the burette to the full line and we ventured out again. Well Dan and I placed second in this 50 car run with around 100 miles per gallon. A couple of guys from one of the magazines out did us by a couple of miles per gallon. I think they ran a bit more air in their tires but they used the same techniques. We did show VW that we could get good mileage but it did little for the certification of the Up Shift Light. And we broke speed laws and really had a ball.
The moral of the story, which is a true story all the way, is that determining a difference in fuel economy means measuring apples against apples under like conditions with only one variable at a time. Driving cost over an extended period of time is a valid number.