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Old 04-17-2011, 11:52 AM   #13 (permalink)
utemarksman
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Join Date: Mar 2011
Location: Utah
Posts: 3

ベカちゃん - '06 Subaru B9 Tribeca Limited
SUV
Subaru
90 day: 22.52 mpg (US)

DonQui - '00 Ford Mustang Base V6
Team Mustang
Team Ford
90 day: 33.13 mpg (US)

CRLY - '98 BMW 740 iL
Team BMW
90 day: 20.81 mpg (US)
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Good work on meeting your goal!

I just thought I'd chime in since I am also approaching my milestone value. (30mpg)

I drove my 4-cylender '98 Rav4 by ear and did fairly well at 28 mpg in the winter and 32 mpg in the summer (although that number could have been improved on if I hadn't stripped out 5th gear). Having the manufacturer installed gauges in my Tribeca has helped me adjust my driving style from good to better. Now, with the 6-cylinder Tribeca, I'm hoping to eventually get the same mileage.

As a note on the tire pressure; the manufacturer lists 33psi and I run 38psi. I've tried to run higher but the TPMS lights up when the pressure exceeds 40psi. Starting cold at 38 I find that it doesn't warm up enough over my commute to exceed the 40psi threshold. I religiously check the tire pressure with every fill up. Fortunately my service station is one of the few left that offers free air, so an adjustment of 1-2psi in one tire doesn't put me out $.75 each time to run the compressor.

As a note on re-fueling; Definitely be as consistent as possible. I will go as far as filling up at the same time of day at the same pump at the same station whenever possible. Usually in the early morning when the station is less busy and the ambient temperature is cooler. I've always understood that their was a temperature expansion factor on the fuel but initially thought it was insignificant. That changed when I had to calculate that temperature-expansion coefficient as part of a chemical engineering homework assignment. Remember, your fuel is sold by volume not by mass (weight). I will admit, if your regular commute is short, the expansion factor doesn't really amount to much. However, when your driving over 25k miles per year, the higher cost of less dense fuel eventually adds up.

A note on significant figures; As other posters have noted, accuracy in measurement is vital for retaining significant figures. If there is variability (or "error") in your measurement it reduces the number of significant figures that you can report. At best, for my own uses, I can only justify reporting to one tenth (0.1) mpg and that's probably pushing it. As a side note, my manufacturer-installed computer will only resolve three tenths (0.3) mpg. (With a systematic calculation error of 0.7mpg above actual.)

Another useful tool is the fuel log in the "Garage" section on this site. It allows you to track your FE history. If you keep notes with it it will allow you to see trends. It also allows others to see how you're doing especially if you note the mods or causes for change in the comments sections.

Congratulations on hitting your goal. Now that you're there, do you have plans on improving on that number?
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