Michael Ross wrote:

> It is a bit of a bugaboo that weight is important in terms of energy
> consumption. More important is air drag losses, and rolling resistance.
> In the thought experiment where there are no losses to friction, the
> weight is meaningless except for whatever change in elevation there is
> from start to finish - if you go down overall you actually benefit from
> greater gravitational potential at least for that trip. But, it is
> really a wash in the theoretical sense..
> Yes, it takes more energy to get the heavier vehicle up to speed, but that
> is then inertia, and you get it back with some regen instead of wasteful
> brakes, or you get it back not losing as much speed when going downhill.
> The weight can add to rolling resistance (losses to heat in the tires),
> but this is really second order stuff.  If the heavier car is smoother
> in the air that is very important.

I think you may be being confused by the fact that rolling resistance is 
(relatively) independent of speed while aerodynamic losses increases 
dramatically with speed.

At higher speeds, aero losses will dominate and so can make it appear as though 
rolling resistance is unimportant, particularly if the vehicle is not all that 
aerodynamic.  As vehicles become more aerodynamic, the rolling resistance 
becomes a more significant portion of the total losses.

Rolling resistance force is *directly proportional* to the force exerted by the 
weight of the vehicle normal to the road surface; this is not a second-order 

Similarly, while *some* of the potential energy gained due to an increase in 
elevation or kinetic energy gained during acceleration can be recovered through 
regen on the descent or deceleration, not all of it can be.  The inefficiency 
of the drivetrain works against recovery of energy just as effectively as it 
works against the delivery of mechanical energy in the first place.



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