^^IME it depended on the season. Late spring, Summer and early fall when the weather was warmer I always got a few extra tires as compared to the colder months. On average when I was running 31's, I would get about 28 tires from 15-35psi, and about 16 tires 5-35psi. With 32's it was about the same, but with 33's it was a lot less, about 20 and 12 IIRC. When I was running CO2 we used to wheel about 3-4 times a month, so I averaged about 4 20lb fill-ups a year.
You might consider running two set-ups, the CO2 for re-seating beads/airing up, as well as running one of the MV50 12vlt electric compressors. They are slow, but work well enough, and would help stretch the CO2, or fill in if you happened to get caught running out of CO2 on a run.
