My real undisclosed inventions evolve around building a car based on my absolutly redicoulous phylosophy that a car engine should be about 500 gram in stead of 500 kg. I've assumed this position as it allows me to search for ways to make the relatively much more ridiculous "current" car designs at least a few 100 kg more efficient. For example, what we call aerodynamics is probably the most amateurish profession we have. As the reality of the tornado can not be denied neither can the self powered vortex engine of Victor Schauberger. Jacques Cousteau's Calypso II could sail upwind beyond any doubt. So, it should be possible to build a self-sustaining vehicle shape with less then zero drag. For starters, why not fill the body with helium?
It turns out that helium is a lot lighter than air. The difference is not as great as it is between water and air (a liter of water weighs about 1,000 grams, while a liter of air weighs about 1 gram), but it is significant. Helium weighs 0.1785 grams per liter. Nitrogen weighs 1.2506 grams per liter, and since nitrogen makes up about 80 percent of the air we breathe, 1.25 grams is a good approximation for the weight of a liter of air.Howstuffworks "How Helium Balloons Work"
There already are bike frames with helium.
.....An empty car can be something like 10 kg. :-)