Quote:
Originally Posted by jimepting
....I studied your chart and I see a couple things which don't look quite right. First, there is some inconsistency at the 60&70 psi level. In both cases, there were two significant outliers.
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I think we are seeing the repeatability of the test itself. This result does not surprise me, after attempting to perform repeatable coast down tests for several years and coming up short based on my limited measurement techniques.
Quote:
Originally Posted by jimepting
...Second, not mentioned in the methology was warming up the transmission(I guess it has one) and tires. By starting cold and doing the tests in a reverse order of pressure, there is a bias injected in favor of the low pressures.
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I see what you are saying Jim, but I also think that because it takes time to change the air pressure in those tires between each test, that the transmission will not really get warm during each coast down test. There is too much time in between each trial for the heat to accumulate.
So in this case, it may be more desirable and consistent *not* to heat the transmission as it will just as cool for each coast down.
I suppose one could *randomize* the order in which each test is run in order for any *heating effect* to reveal itself in the data.
Quote:
Originally Posted by jimepting
....A question that remains unanswered it "Does roll down distance equate directly to fuel economy?" I'm not at all sure we know the answer to that, but hypermiles, by their actions, vote "no."
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My educated guess would be that coast down distance is proportional to over all fuel economy. Why?
When I do P&G on the way home sometimes, my fuel mileage is highly influenced by how far the car coasts with the engine off. When the ambient temperature gets into the 100's(F), it's amazing how much longer the car coasts on the same stretch of road compared to spring/fall/winter temps, and my gas mileage seems to reflect this.
Look at my seasonal gas log for evidence of this.
Just my observations.
Jim.