I know they're doing it with
nitrogen -- the idea being the tires will not lose air quite so quickly.
Helium, according to a
NASA quiz, should be good for bikes!
Here's another site where some
aeronautical engineers discuss the pros and cons of helium-filled tires. It seems that it will depressurize rather quickly . . . a bad thing . . . but maybe not so bad for crits??
See ya' at the top!