Re: metric conversions

[Jeff Goss <jjgoss@xxxxxxxx>]

Neil Lindsey wrote:

> 
> > A long time ago I figured out that a magic number for converting l/100km
> > to IMPERIAL mpg.  The number is 284, and you divide whatever figure you
> > have into to get the other since they are inverse measurements
> 
> Around here not too many people even think about km/100 litres (unless
> you're looking at the sticker on a new automobile that is).  I was
> interested in such a magic number for deriving MPG directly.  I think that
> if you tighten up on the specifications you will see that the number
> actually works out to 282.4.

Looks like rounding error by the number of decimal points.  Of course,
too much math can introduce new errors, as in the extra digits one
lister posted when converting Imperial to US - the number is 4/5 or 0.8,
unless there is a thousandth of a percent or two difference in our
ounces!

I probably won't change my numbers to another decimal point or two,
since all I generally do is a little mental math to check when I want,
where I lose much more than the 1/2% or so.  Factoring in the slop from
differences in filling levels on such a small tank and the fact that
they actually adjust the 'volume' of a litre here to as if it were
pumped at 15C, I don't imagine my little fudge matters much.  Shh, don't
tell anyone but sometimes I just use 280 (mental math can only carry so
much precision!

At least now we have two backups for the numbers and two methods of
doing the conversion...

> 
> What I do is simply divide the number of km I have ridden by the number of
> litres it took to fill the tank and multiply the result by 2.824.  This will
> compute MPG (Imperial).  If you prefer to deal with US gallons, then the
> magic number becomes 2.3523 (or in your terms 235.23)
> 
> Your conversion factors are ok for rough comparisons, but when I compute my
> mileage I want to know exactly what it is
> 
> If you're interested, the math looks like this:
> 
> one mile per Imperial gallon = 1.60935 kilometres per 4.544 litres
> one mile per Imperial gallon = 0.35417 kilometres per litre
> therefore:
> one km/l = 1/0.35417 mpg = 2.8235 mpg (Imperial)
> 
> one mile per US gallon = 1.60935 kilometres per 3.7856 litres
> one mile per US gallon = 0.42512 kilometres per litre
> therefore:
> one km/l = 1/0.42512 mpg = 2.3523 mpg (US)
> 

- -- 

Thanks.

Jeff Goss

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