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Old 08-29-2012, 02:25 PM   #28 (permalink)
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The Mistress - '88 Bmw 320i Touring SE
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Originally Posted by MetroMPG View Post
It's interesting to noodle the graph...

But I'm not sure using average speed as a measurement over an entire tank works well as feedback to the driver unless the tank is predominantly highway/rural cruising, and other tanks results are over the same/similar route. (IE - controlling for as many variables as possible.)
The reasoning I decided to measure tank to tank average speed are as follows

1.My range is only 230-270 miles, circa 1 weeks driving

2.I have a basic commute of 250 miles a week- same routes at the same time of day. Therefore the majority of data was recorded on the same return journey

3.The car has a built in average sped function on the OBC

4.Variables I cant control are so large and vary so much over the course of a tank that they even out (e.g. so far this week I've had 2 dry partial commutes (one out, one back not on same day) and 4 wet ones) no to mention the temp going from 20 degrees to 9 and back to 14 in the same 3 day period.

Then there's the traffic and accidents...25 miles in 55mins today

EG: if a tank includes a siginificant mix of city/suburban plus highway motoring, how do you interpret the results & use the average speed number to your benefit?
The average speed figure represents (to me) a function of the above noted components, allowing me to guesstimate fuel costs, and review budgets. I can also check the average to see whether can afford a "spirited trip" home, or whether I have to be mega frugal

Also: does the measurement of average speed include time stopped? (EG: the ScanGauge average speed calculation is not a "rolling" average, which would be more useful. Its calculation includes time stopped.

Consider too that spread out through the year, weather effects will affect the MPG numbers (cold weather = worse mileage; warm = better). How is that separated from the average speed variable?
My ccars OBC counts it as "Key on" speed- essentially if stationary but at position II on the ignition, its calculating..

as above, I've decided that the Scottish weather its too much of a task for one man
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