Date: Sun, 02 May 2004 10:03:14 +0100
From: Johannes H Andersen <>
Subject: Re: Fuel consumption figures computer wrong

David Taylor wrote: > > > Looking for changes in fuel consumption may be useful. A new air > > filter in my Saab improved consumption by a couple of mpg. Also > > useful for comparing what you get from keeping a constant speed > > 2 mpg over what distance? This is the precise point that's being made. > Can you say that you didn't be just a little lighter on the loud pedal > for part or all of the journey? The answer has to be no because unless > the test is over precisely controlled conditions, you can't make such > claims other than implied. You're quite right that any claim of improved mpg is difficult to establish. The various controversial 'economy' devices is a very good example of how people can be hoodwinked. We only have the primitive tools we've got. Nevertheless, my point was that relative measurements are probably more reliable that absolute measurements since at least the bias is taken out. I drive approximately 35 miles to work, mostly on motorway without stopping, so I can control the speed. I observe not only average consumption, but also the range of consumptions between various days. I know the road gradients in great details and know where I can expect more and when I can expect less consumption. I also know that the consumption can quickly be destroyed by heavy use of the pedal, so I consciously try the obtain the best figures for a particular day; competing with myself if you like. It is not scientific by any means, but with the right attitude and purpose of mind I believe that you can get closer to the truth.

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