Quote:
Originally Posted by Smoky
Apples to apples:
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You do know that force of drag also has a frontal area component? Drag coefficient is only useful to compare shapes.
CdA = Drag Coefficient * Frontal Area
Insight 5.1 square feet
Prius: 6.045 square feet
mpg difference: 16.6%
CdA difference: 18.5%
The other thing is that if a person is that concerned about fuel economy, he often learns to drive correctly. This means that more chemical energy from fuel is going to push air out of the way (and a little to deform tires, but only a little), and less to heat up brake pads (or the engine/exhaust gas with engine braking, or heat up the battery with inefficient regeneration).
If you eliminate braking, the only factor weight will play is in increasing rolling resistance, which is minimal at most speeds a car will travel in comparison to aero. And note virtually everyone here is decreasing rolling resistance by inflating their tires. 45-60psi would be usual. So aero is an even larger factor.
The "fast back crap" will reduce drag by probably 20-30%. It will add maybe 50kg, at most - or 2% of the weight of a typical truck.