Quote Originally Posted by maillotpois

CO2 is heavier than air, you will make your bike heavy and slow if you
use it. Helium is lighter, the only way to go if you want speed and
safety.

If you are willing to live dangerously, Hydrogen is lighter and cheaper
than Helium, but don't smoke while riding your bike if you use
Hydrogen...

Carapace Completed Umber
Lakehurst, New Jersey
I did some numbers. For a 700x23c road tire inflated to 120 psig, you would add 5.5 g (0.19 oz) by inflating with CO2, and save 9.6 g (0.34 oz) inflating with helium, save 10.25 gm (0.36 oz) inflating with hydrogen (H2). Of course, one presume that if you inflate your tire with CO2 while on a ride, you were carrying the CO2 cartidge already and thus you have a net decrease in bike weight of 11 g when you use it (replacing the 11 grams of air in your tire with 16.5 grams of CO2 which you were already carrying). Compare these weight differences to carrying a pump which weighs several ounces to half a pound.