I added a 5lb C02 tank I made up. http://www.expeditionportal.com/forum/threads/117910-5lb-CO2-tank
A 10lb tank is just too big for the Cayenne.
I have the onboard compressor for the spare but a C02 tanks always trumps a compressor. if I get a puncture, I can plug it and fill from the tank faster than a compressor can fill the tire.
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