Quote:
Originally Posted by Vman455
Has anyone proven empirically that in the case of two cars, with identical Cd and frontal area but different masses, the heavier car will roll faster downhill? Does the increased momentum of a heavy car outweigh (ha!) the increased rolling resistance at some point, and where is that point?
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I can answer this one: yes, it absolutely happens.
My truck, empty and just coasting downhill, will v-e-r-y slowly lose speed as it coasts down one particular hill on my way home. I'll hit the top of the hill at 60, turn off the engine and EOC to about the halfway point, bump start and accelerate back to 60, and hold right at 60 all the way to the bottom.
On a few separate occasions I have had firewood in the back, usually 500-1000 pounds. With a half-ton aboard I'm usually only doing about 55 at the top of the hill. Engine off at the top, coast...coast...
coast. At the bottom it'll crack 70 if traffic permits, and the engine won't be needed at all to carry me through the flatter part in the middle.
It isn't identical vehicles, it's the same vehicle. I love when I get this result, too - trips like this were part of the first tank I ever had that cracked 35mpg.