Measure your cars drag.
auto.howstuffworks.com/question497.htm
And `sweetspot` for optimum speed, re fuel consumption
cut & paste
"In general, smaller, lighter, more aerodynamic cars will get their best mileage at higher speeds. Bigger, heavier, less aerodynamic vehicles will get their best mileage at lower speeds.
If you drive your car in the "sweet spot" you will get the best possible mileage for that car. If you go faster or slower, the mileage will get worse, but the closer you drive to the sweet spot the better mileage you will get."
End of cut & paste.
Ref
auto.howstuffworks.com/question477.htm
Any comments?
Regards
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This method is one which has been looked into extensively by researchers at what was formerly known as the department of Transport Technology at Loughborough - they have developed a number of refinements to make the technique deliver meaningful results. The outline of the method as quoted in the how stuff works page is correct, but, without the refinements in technique will only give very approximate results.
As the method described doesn't cost anything, by all means try it - but think carefully how many decimal places you choose to quote the resulting CDA values to!
Number_Cruncher
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"will only give very approximate results"
And will require a very level road! More common in the US perhaps...
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I have/had a good example of this, having owned a Citroen GS estate that was regularly used for the 350 mile round trip from the Isle of Wight to Cambridge while my daughter was at college. The car was inevitably filled to bursting point, but could manage the same top speed (about 100) laden or unladen, with a mere 65hp, as the hydraulics ensured that it always remained level. It's successor, a Peugeot 305 GT, had 50% more power but could not manage the same speed with the same load, as the nose-up attitude destroyed its aerodynamics.
My current Xedos seems very slippery, with very low wind noise and that strange quality of seeming to get quieter as it goes faster. An illusion, of course, but agreeable all the same...
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If you are keen JBJ, try searching for papers on coastdown by M A Passmore - the subtleties are explained there. Among these extra refinements, for accurate results, it was found necessary to measure local values relative air velocity.
Number_Cruncher
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Don't be fooled by what you think is an "aerodynamic" shape. Some modern boxy hatches have a drag coefficient lower than that of an E type Jaguar.
--
L\'escargot.
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"In general smaller lighter more aerodynamic cars will get their best mileage at higher speeds.
At a constant speed, it'll make hardly any difference at all.
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