Weight reduction - not always good?

[bbgobie]

Ummm... If your car is super heavy you need more force to accelerate it. Yes it can hold momentum better which is what I think your getting at, but the over all picture of mass is miscalculated here. The energy requried to accelerate a 1 gram car is minimal. It'd take my whole tank of gas to accelerate the 100,000 ton car to 60mph.

[landspeed]

Originally Posted by bbgobie

Ummm... If your car is super heavy you need more force to accelerate it. Yes it can hold momentum better which is what I think your getting at, but the over all picture of mass is miscalculated here. The energy requried to accelerate a 1 gram car is minimal. It'd take my whole tank of gas to accelerate the 100,000 ton car to 60mph.

(I have also read the other posts above).

What I was getting at is a 'sweet spot'. In fact, the idea is that there is a sweet spot for economy. The 1 gram car will actually be worse (aero drag stops you coasting at all), and the 100,000 ton car would be rubbish (due to massive rolling resistance).

The question is, where is this 'sweet spot' - it will be different for each car, and it is pretty unlikely that the car designers will try to achieve it.

The best idea would probably be to reduce aero drag as much as possible, and fit low RR tyres, keeping momentum, but using low RR tyres, and spending most of the time working on Aero rather than weight. Although in stop-start driving the other way round (work on RR *and* momentum) would be more appropriate.

Interestingly.... If RR was the same on the 1 gram and 100,000 ton car, then, the 100,000 ton car would get the best economy if driven on a very very long straight road. You could put the energy into it, at 40% efficiency, then coast the rest of the way, while the 1 gram car would need the engine to be on all the time, so it would be maybe 22% efficient, so only get half the MPGs