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[ST] Gas Mileage and Standard Deviations



With the recent postings on varying gas mileage, and
observing my own range of numbers (average probably 45-47
mpg, best ever 54mpg US), it struck me that the average gas
pump and the variable level that we refill our tanks to
would be more than enough to account for the range.  Assume
a best case of +/- 0.1 gallons, and thus for a typical 4
gallon fillup, 3.9-4.1 gallons.  Assume 50 mpg true mileage,
and that would result in an apparent mileage of 200mi/3.9 =
51.3mpg, or 200/4.1 = 48.8 mpg ( a range of 2.5%).  Most of
us probably don't refill the tanks that accurately, and who
knows how inaccurate the gas pump guages are.  Anyway, it
would seem like a 0.1-0.2 gallon variability is inevitable,
which would just about account for the published ranges from
everyone.  Of course, many times I have estimated my mileage
when putting as little as 2 gallons, which could easily give
an even larger error.

I guess the moral is, if one feels their gas mileage is off,
carefully measure somehow a few tankfulls and average it out
before looking for bike problems.

Rick Hartwick

amateur mathematician (Dietzgen Microglide slide rule lubed
with 4T oil)
00 Sprint ST


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