Weight reduction - not always good?

[samandw]

Sorry to resurrect an old thread, but I'd like to make a point I didn't see made in the preceding replies.

Given two cars identical accept for the weight, the heavier car will have a greater ratio of weight to aerodynamic drag. When coasting down hills, the propelling force is a proportion of the weight of the vehicle. Where aerodynamic drag is the predominate slowing force, a heavier car could maintain a faster speed down a given slope. Why is this important? Well, because if one car maintains 52 mph EOC'ing down a given slope of the freeway, and the heavier car maintains 60 mph down the same slope, if the driver wants to maintain the minimum 60 mph in order to avoid causing a traffic disruption, guess which car burns less fuel? You guessed it, the heavier car, because the light car will require the engine on and at light throttle to maintain minimum speed (inefficient area of the poweband), while the heavy car will have the engine off.

Just some food for thought.