Quote:
Originally Posted by 2000mc
Sure you could have vehicles with the same rolling resistance and wildly different CD, but when I think of specific examples they seem to have a positive correlation. You say .5 CD I’m thinking hummer H2 has some serious rolling resistance, You say .25, I’m thinking insight.
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Yes, you are right - I was exaggerating so people could more clearly see the point. But what about 0.28 vers 0.35, or 0.25 versus 0.30 (etc?). You can see that rolling resistance will often be little different, so the same illogicality applies.
Quote:
Originally Posted by 2000mc
I always thought the 5/10 was more just a rule of thumb
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Rules of thumb expressed in precise numerical relationships is, I think, really dumb. There is typically very little evidence that supports them, but their simplicity is seductive. A dangerous combination!
I cover the topic here -
Deceptive Rules of Thumb in Car Aerodynamics: