The inner diameter of a 40 cal. bullet shell happens to fit nicely over a valve stem cap. All you have to do tap the shell onto the cap with a hammer. These went to the same friend who got the retractable bullet pen.
Safety first: The shells were already expended by the time I got them. Never attempt to use a live round for any kind of project. Serious injury or death can occur.


































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try to weight that empty shell, I'm sure it's more than several grams and the weights for balancing are stepped by 5 grams.
50 km/h divided by 60 minutes is approx 833 m / min divided by the length of 16" (40cm) wheel is 833 m / (0,40 m * 3.1415) is 833 m / 1,2566 m is about 662 rotations per minute. http://www.google.sk/search?q=(50000+%2F+60+)+%2F+(16+inch+*+PI)
Driving at highway's allowed 130 km/h makes nearly 1700rpm. http://www.google.sk/search?q=(130000+%2F+60+)+%2F+(16+inch+*+PI)
Attach 20cm ribbon to an 10g screw and try to rotate it at approx 5 rpm in your hand (which is pretty fast) to get the feeling about the power of centrifugal force. And now imagine the power of centrifugal force that is applied to axis of the wheel by every nonbalanced gram of weight at highway speed.
adjective Physics
moving or tending to move away from a center. The opposite of centripetal .
great idea though!
But seriously . . .who needs air in their tires really? ;^)