I have witnessed on a number of occasions people attempting to use CO2 fillers that hadn't practiced in the privacy of their own garage prior to taking the show on the road. I fell victim to my spare tube having a hole in it and using up both of my cartridges before I realized what was happening. And I was saved at the bottom of Mt Diablo by generous bicycle brotherhood. I now carry two tubes and three cartridges, plus Park self sticking patches. Someday I will return the favor to someone else, I always ask as I pass.

On another note CO2 cartridges are reasonably priced if you buy in bulk off of eBay. I got 30 16 gram threaded mil spec for $25.00 shipped. Sure beats two for $9.95 at LBS. And I use the PlanetBike Air Kiss filler which works OK for me.

jw