Could cars be designed with extra large donut tires filled with helium to make them lighter and more fuel effi-cient?
Great Idea, we could also make the cars out of rubber and that way they would just bounce if they run into something.
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At which point you find that the extra large tyres are heavier than standard ones.
The air in a tyre is not very heavy compared to the tyre (though for safety reasons it does need to be inflated to the right pressure).
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Helium doesn’t really have enough lifting power to make a big difference. To get an average person off the ground would take about 8,000 regular-sized helium balloons. And of course a car weighs much more than a person. Even with giant monster truck tires, you would see little difference. Way to think outside the box though. Keep at it.