I know a few people have brought air tanks (scuba?) to trails to air up a tire after they wheel... I just want to get a good idea of how much volume it takes to air 4 tires back up to 40lbs or so. I also wonder if a 15inch wheel will be a lot more than a 16 with the same tire size? I can see it logically would be more, but I wonder how much? also a side note... how much do you guys air down when you go wheeling?

I'm assuming you mean the same diameter and width tire, not the same tire size (like, 30.5" x 10.5 or something, not 245/75R16 vs 245/75R15, since those two sizes will be off by an inch of eachother).

so with a tire of diameter D, width W and rim-size of R (15 or 16)...

Air held in either tire is (approx) ( (pi*(D/2)^2*W) - (pi (R/2)^2*W) ) = (pi*2*W)(D/2 - R/2)

So if you were to figure out the difference between the 15" and 16" tire, it would be that 1" difference: pi(R/2)^2*W - pi((R-1)/2)^2*W = pi(16/2)^2*W - pi(15/2)^2 * W = 201*W - 177*W = (24*Tire Width) cubic inches

Obviously there's a lot of room for error there, I'm assuming that the rims are the same width, tires are the same width. I'm not even taking tire pressure into account at all

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Jeff 2005 Jeep Liberty Renegade
4x4, 6spd, Leather, Sunroof, trak-loc, skids/rails, hitch+shackle, hooks, Alpine/iPod, Thule, GPS, CB, Frankenlifted w/ 31" MTRs
Photos Cardomain

when you see some one witha "scuba tank" that is CO2 i think that a 15# CO2 tank can air up over 30
33X12.5X15's from 15 to 30 psi they can also run air tools and are refillabale for about $10
however they cost $200-$400+
if all you want to do is air up tires i would go with a small viair air compressor they start at the same $200
and can go over $500 but they never need to be refilled and if you go with an ARB locker their compressors
star at $175 but all they run is lockers but you wont need to buy theirs because the viair will work just fine
make sence?
i have the viair and an ARB compressor for my locker

I got a Viar and a 5 gal 4 port tank for bagin out trucks... I just wonder if 5 gal of normal air will re-inflate a set of tires. I know the CO2 is a different ball game so i guess that compairison is out of the picture.

I figure I will fill the air tank, before I leave for trips... and plumb the compressor from under the hood to the tank to re-fill it when needed. The duty cycle is not the greatest on those little viar compressors so I dont think they will inflate 4 tires all at a rip.

Tonight I will fill the tank... air down and see how many it will fill with 5gal of air.

Don't forget that everyone airs down their tires to differnt pressures. That means airing up will vary from tire to tire to size to size to weight to weight to tire pressure to tire pressure to temperature to temperature....etc.....

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New KJ Gear - Desert Armor Flak

2004 Renegade Light Khaki - 4" JBA Lift - Rock Lizard Products: Komodo Dragon Rear Bumper, Prototype Winch-mount Front Bumper, Super Skink Sliders - All J's Super Tranny Skid II - 31" Firestone Destination AT's on Moab wheels - Cobra 75W CB w/ stock Antenna mod

[b]Retired, US Military

if you have the compressor and the tank it dont matter how many tires the tank can inflate the compressor will re fill it when the pressure drops below the min pressure setting