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June 2008
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A couple of days ago I wrote about some drivers and their sometimes perplexing habits on the road. I guess I'll keep a similar theme for this entry because driving has something I have been thinking about a lot lately. Why, you ask?. Well, the reason is simple. It's the cost of gas. Like everyone I'm not happy with the price of gas lately and am always looking for ways to improve my gas mileage. A few years ago I went out and bought a hybrid car. Because of that I get almost 50 miles to the gallon but with nearly 500 miles of commuting per week I am still looking for ways to cut the big bad gas bill. A few months ago I read a story about how not back up could save you up to 10% on your mileage. What I mean by that is that you pull into parking spots where you can pull straight through and never back up. You also park on the street instead of pulling into your driveway. It seemed impossible to me but I started doing it and my mileage did improve significantly. It didn't go up 10% but it was very noticeable. That may be a little too much trouble for some people, but there is one thing you can do that is very easy and will give you even more bang for your buck. It's called going the speed limit. It turns out that force increases with the square of speed. What does that mean in laymans terms?. Well, it means that it doesn't take twice as much energy to go twice as fast, it takes 4 times more. In other words, if you are travelling 25 mph you are using a certain amount of gas depending on the type of vehicle you drive. If you increase your speed to 50 you don't just double the amount of force the air is exerting on your car, you increase it by 4 times what it was at 25 mph. That means going 65 instead of 55 doesn't just use 18% more gas because it is 18% faster. The bottom line is that by driving the speed limit instead of 10 miles per hour more than the legal limit you will improve your gas mileage by quite a bit. If you drive 15 over then you will find an even bigger savings. It's like instantly paying $2.50 a gallon instead of $3.00. Who wouldn't find that enticing. You might also be amazed at how much lower your stress is as well. I used to speed, and since I started driving the speed limit it is amazing how much calmer I am while driving. And I like saving the 50 cents per gallon as well :-) 1 CommentsLeave a comment |
You'll find that most cars are at maximum fuel efficiency at about 45 MPH. This is due to the fact that engines are most fuel efficient at a particular rpm and then take into account the gear ratios in the transmission that move the vehicle along the road. Once up to speed, it takes very little horsepower to move the vehicle along. I've read that only about 15 to 20 horsepower is necessary to keep a car moving at 55 MPH. Also, once rolling, most of the power used is not moving the mass of the vehicle, but overcoming wind resistence and tire friction. (ask anyone who ever built a pinewood derby car about drag and friction) That's why a few years back, the drag coefficient of a vehicle was very often published and used as a selling point. A drag coeffienct of .4 was considered to be pretty good if I recall correctly. I wonder why they don't publish them anymore? Probably because all the SUVs on the road have more drag than the sails on Mayflower that brought the Pilgrims here.
Tim
Chesapeake