10lb co2 tank.

[Stumpalump]

I have heard that CO2 leaks out faster ( not sure about that) or even worse its not as stabil with temps when in your tire. In other words the pressure swing between a cold tire and a warm tire is more dramatic than with air and nitrogen is the most stabil.

 

[BigSwede]

Yeah, but in real-world use I don't think it matters that much unless you have a race car.