Letters to the Editor
zzz05
Published Letters: 413 Editor's Choice: 9
-
jackrabbits are highly efficient animals
[Read the article: How to get better gas mileage]
[Read more letters about this article: Here]I'm sorry, but this is one of those urban legends; anybody who's looked into the physics or engineering of the matter can tell you that the gasoline engine is most energy efficient at full throttle and gets less efficient with smaller throttle openings, for the simple and obvious reason that it takes a lot more energy to try to inhale a couple of liters (at least) of air a few thousand times a second through a little gap the size of a pencil lead than it does through a big wide open pipe. That's the reason your car slows down when you get off the gas pedal, not "compression braking", which is physically impossible (air is highly elastic, you get almost as much energy out when you compress the air as you put in). That's also one reason diesels, which don't have any throttle in the air intake at all, are more efficient.
The inefficiency comes in overaccelerating to where you have too much speed, and having to lose it via the brakes. Thus the correct instructions to anticipate stops and start coasting down early. But if you need to accelerate to a speed and hold it, the most efficient way is full throttle, shifting up as soon as you possibly can; low rpms and wide open throttle are obviously the most efficient way to pump air. Of course, with the huge engines they sell these days, it's tough to keep from overshooting; small engines are more efficient is just another way to look at the same thing.
Basic high school physics: To accelerate a certain mass from 0 to a certain speed requires a certain amount of energy, which requires a certain amount of fuel to combine with a certain amount of oxygen, out of the air. That's all that enters into it; the mass of the car, and the net difference in speed. Whether the acceleration is fast or slow doesn't enter into it. But: it's more efficient to inhale that certain amount of air through a small pump (i.e. engine) with a wide open pipe (i.e. full throttle), than through a big pump with a cork blocking most of the pipe (i.e. partially closed throttle). That seems obvious. But it's also more efficient if you're stuck with a big pump to move that air with a wide open pipe than one with a cork in it, even though you get the total amount of air moved more quickly. Which means that, for a given engine in a given car and a given change in speed, full throttle acceleration is more efficient than gentle acceleration to the same speed.
In fact, if you look at those fuel efficiency competition cars that get ridiculously high mpg, the way the stock ones are driven is to accelerate with wide open throttle to about 40 (where wind resistance begins to get severe), shut off the engine and put in the clutch and coast down to a few mph, then let out the clutch and turn on the ignition, which starts the engine, and accelerate full throttle up to 40 again. Repeat as necessary. Very different from the "gentle acceleration" so frequently recommended. And the purpose-built fuel efficiency competition cars don't even have throttles; they just have tiny engines which are operated using the above technique.
Caveat: some? many? cars are set up by the factory so that extra fuel is supplied at full throttle, on the supposition that you've floored it, you must want all the power you can get. How much, and what difference it makes, and where it starts to kick in is highly variable from one model of car to another.
-
and another thing
[Read the article: How to get better gas mileage]
[Read more letters about this article: Here]Also, of course, if you think about it, automobiles are at their most efficient in long distance travel on the interstate, and least efficient in the cities. On the other hand, when moving people from home to work, when 20 different people who live in the same neighborhood work in 20 different companies in 20 different locations, it's a lot tougher logistically to do it with a bus than it is to move people from their homes downtown with a bus; it's tougher to commute 30 miles by bike than to ride downtown; etc. So, practically speaking, ramping up mass transit, bike lanes, downtown walking malls, etc. seems a lot more doable right now, but I'm afraid the average person kind of blocks that out and figures he/she can just keep driving their car around everywhere the same as they do now but get 100 mpg.
In the long run, I suspect pursuing better mileage for cars so that we can all put on our average 30 miles a day because we have to drive all over Hell and back to get our daily chores done is a losing proposition compare to just unsprawling ourselves, with all the added benefits regarding land use, etc.
-
Goldberg book
[Read the article: Various items]
[Read more letters about this article: Here]"'jackbooted stormtroopers'—such are the insults typically hurled at conservatives by their liberal opponents"
-Random House blurb for "Liberal Fascism"
Ah, isn't 'jackbooted stormtroopers' the epithet the ultrarightwingnuts used for the FBI and cops at Ruby Ridge?