Quote:
Originally Posted by Ken Fry
......Unless you have really awful tires, your Crr cannot be .0137 -- so this figure is taking into account final drive and transmission friction, which is not perfectly constant -- part of it is hydrodynamic. The usual coastdown test calculations assume one constant drag, and one exponential......
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One other forum member calculated that my Crr should be closer to 0.008 or so, and this seems reasonable if it's warm outside.
The above Crr of 0.013 that you are referring to is probably fairly accurate because this was measured in the dead of winter, during some very cold temperatures. Obviously the Crr in the winter will be at least 20% greater than in the warmer months in the summer. This was pretty obvious from all the coast down tests, whether I published the results on EcoModder or not.
Surprising, the Cd did not change as much, since the equations listed on the Instructables consider barometric pressure and temperature (air density) and thus correct for any change in these values, giving a reasonably stable Cd number, no matter what season the coast down testing was recorded.
At this point in time I have no reason to either agree or disagree with my findings, but simply publish what I found, so for me a more thorough investigation will need to wait until a more refined process is developed.
Jim.