Quote:
Originally Posted by Ecky
I enjoyed his thread, but there was a *lot* of hyperbole. Suggesting a massive difference in how the car handles turns by removing "parts of the headliner" ? Good ideas, and I'm certain many of his mods helped, but it reads strongly of placebo as well.
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If a person who travels around town (Urban Driving) 98% of the time sticks a boat tail on his car and then posts: "Look my great mpg on the highway!", what do we call that..? 
The same might be said for, for eg: heavier Flat Bottoms..? And..???
Which is the original question!
My point is;
we simply cannot get around the laws of physics:"...What is more significant, however, is that at each level, the actual tractive energy is strongly dependent on vehicle mass, through its influence on the rolling and inertia components. This gives mass reduction high priority in efforts to reduce vehicle fuel consumption...
In the UDDS (urban) driving cycle: (98% of driving)
Rolling Resistance (%): 19
Aerodynamic Drag (%): 14
Inertia (%): 68
In the HWFET (highway) driving cycle: (2% of driving)
Rolling Resistance (%): 29
Aerodynamic Drag (%): 47
Inertia (%): 24
https://nap.nationalacademies.org/re...4/chapter/4#20
Examples to consider:
No mainstream car is going to beat the economy of an E-bike or small motorbike around town and those have the aero of a small parachute!
Then we have velomobiles:
Unbeatable aero, light vs a car, but do cyclists on bicycles (same power, less weight) still leave them behind in stop/go town driving..? It seems so!
If you want to add to your "I don't know where to draw the line" shrug; add hub-motors with regen to the velomobile consideration.
Now the velo's better aero improves regen.
But as 'proven' (should be similar to town driving) in the
hilly country road tests for economy; lightness still wins over more regen!
To me it seems that making parts of the car (weight) that you would be carrying around anyway, more aero (do double duty) is the way to go.
With adding weight to improve aero there's a fine line as to where to stop.
That fine line seems to be drawn be car manufacturers funding research on their specific questions at universities etc.