We Test the Tips
Edmunds.com
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We Test the Tips
With fuel economy in mind, Edmunds.com drivers test the top four gas-saving tips — and get some unexpected results.
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If you repeat any of them, could you make the following changes? (Some are very hard, or very numerous, to do though.)
Test # 1: Please don't mix changing the braking with the acceleration. Which part affected the results more? No way to tell with the way you tested it. Might have to run it as two separate tests, as brake/accel combinations can multiply very quickly.
Test # 2: Great test: same path, both directions. Could you test other speeds? One old study ( table form: http://cta.ornl.gov/data/tedb29/Edition29_Chapter04.pdf page 4-31, or graph form: http://en.wikipedia.org/wiki/File:Fuel_economy_vs_speed_1997.png ) shows speed matters, but three of the nine tested cars got better mpg at 60 than 50, and one car got better mpg at 65 than 55. However, those cars are now over at least 13 years old, and new cars might have shifted their peaks.
Testing as many cars at as many speeds would be very time consuming, but testing an SUV, hybrid, and either a sedan or coupe should be enough for a general idea if you run it again.
Test # 3: How much did you vary between 65 & 75 not in cruise control? Any braking? How heavy was the acceleration?
Could you test CC on hills and mountains to back up your statement on not using CC in mountains? How hilly/mountainous does it need to be for CC to be worse? How much worse is it than "normal" no CC driving?
Test # 4: What about AC off, windows up? AC on vs AC off is asked far more often than the two you tested: comparing the three would be the best. Also, what speeds was the second (20 mile loop) set run at, and if different, did the speeds make a difference? If not different, could you test different speeds? What about testing AC high (or 65 for auto) vs AC low (or 75 for auto) also? How about a low HP car vs the medium-high HP cars you tested?
Test # 5: Great test, and great you deflated even more when it first didn't make a difference.
Test # 6: Good test. Just a wording question. Was the 2 minutes the total for the 10 miles, or for each stop? It sounds like each for the turn off motor, but like a total for the leave in idle.
I'm most interested in tests #1 and 2, greatly, and a little on test #4 since my car has auto climate control, and I have less direct control of AC than I used to.
Thanks for doing the tests in the first place. I hope you spend the time and effort to redo some of them, with an expanded range of cars and improved testing methods.
1. I drove a convertible with top down & AC off, then with top up and AC on. Top up netted noticeably better MPG.
2. Excessive use of the stater can cause premature wear. How much? I don't know. I do know some starters are expensive to purchase and replace. A failed starter on a clod winter night, in the middle of nowhere, is not worth an MPG or two.
The reason being most of your fuel is used during acceleration, and whether you accelerate slowly (35mpg for prius) or quickly (25mpg), the worst you can possibly do is get 20mpg (prius), whereas the sooner you can get up to cruising speed, you can get conceivably get infinite mpg during the saved not accelerating slowly.
I've tried the 'egg under foot' method of 20-second acceleration in the prius, and I get ~5 MPG less on a tank. The Prius teaches you that it's all about cruising, and if your car has an instantaneous MPG gauge, you too will see the same results in your car. Try it!