mattyfatty182

Looking to do some snow runs this weekend. I don't want a compressor yet, but I was looking at buying a 10 gal 135 PSI air tank from sears.

http://www.sears.com/sr/javasr/produ...id=00915201000

Like I said, could I bring 8 tires (all 31' s) back up to 30 PSI from about 15, or am I SOL?

Jeffires

I had one of those, and once the gauge dropped below about 60psi or so it was hard to bring up a tire- the valve on mine was always acting funny though.

SoCal4Running

for 8 tires your SOL

mattyfatty182

Damnit

I'll ghetto 'wheel it though. I'm bringing the whole compressor...tank and all. 30 gallons at 150 PSI should be enough, eh

edit:
Yeah, that's going in my bed.

hotlavaaaa

How about a hand pump? Just a thought.

digital0ne

bicycle kick pump strapped to the front grill. makes the babes go woohoo!

seriously thought...

I'm curious as to why you are staying away from a compressor... any particular reason?

mattyfatty182

Too expenisive, and I don't wheel enough with 31's to justify airing down all the time.

It would be nice, but it's money better spent somewhere else.

mt_goat

I'm going to guess you could air up 2 31"tires from 15 to 30psi with that tank before the process started going very slow. But that is just a guess.

mike_d

if i did my math right a 31x1050x15 tire is about 25 gallons. so to fill a tire to 30PSI above atmospheric pressure would require 50 gallons of air. (atmospheric pressure is about 15PSI. so you need 2x the air at atmospheric pressure to put 30PSI in your tire).

but since you only want to go from 15 to 30PSI in your tire, you'll only need 25 more gallons. so 8 tires * 25 gallons is 200 gal of atmospheric air.

the 10gal tank at 135PSI is equivalent to 90gal at atmospheric pressure.

so in the best case you could get 4 tires from 15 to about 28ish PSI with that tank. but it would take a very long time because by the time you got to the last tire, the pressure in the tank would be so low that it would take forever for the air to go into the tire.

note: this is just a rough back-of-the-envelope calculation to get an idea of how much air you need.

4Hummer

Why not just use an electic air pump. the one that plugs into a Cig lighter ?

Thats what I use. takes awhile. But it gives you a chance to chat with your buddies about the trail, and check over your rig for any damage.

Takes me about 45 min to air all four tires back up to 30 PSI from the 6 psi I run em at.

mattyfatty182

So from ~15 it would take me probably 20 minutes. Two cars is going to be 45 minutes on the safe side.

I already have this compressor, and it's here at my house. I don't want to buy something that I don't have to (ie those cigarette lighters compressors)..it's easier to just throw the big compressor in the bed; plus it will give me some wieght over the rear axles!

jimbo74

its not going to work, a air tank wont use all of its pressure or air... it will work to a certain point, then the pressure inside the tank will be equal or greater than whats in the tire and you will be screwed, spend the $10 @ walmart and get an electric one... watch out though, they heat up... you might need to let it take a break when topping off your tires, in addition to the big ass tank you are bringing with you

4Crawler

iTrader: (3)

I have the full scoop on how much air is needed for filling various sized tires plus all the math worked out:

http://www.4crawler.com/4x4/CheapTri...uchAirForTires

That tank would bring 4 - 31x10.50 tires from 15 to ~30 psi.

mattyfatty182

I assume you are talking about the 30 gal (big one), right?

I read most of your page, but math has never been my specialty.

You calculated that a 20 gal at 150 PSI should fill a 4 cubft. tire from 10 to 30 PSI. Okay, so according to your chart a 10.5"x31" holds 2.2, which is rougly half your example. I am also not airing down to 10 PSI, somewhere about 14 or 15.

So I should be able to fill 8 Tires from 14 PSI to 30 (maybe less in the back) with a 30 gallon at 150 PSI?

4Crawler

iTrader: (3)

I picked the 10 gallon tank the Jim mentioned at 135 psi. If you want to see the math, 10 gal = ~1.25 cu.ft. volume and 135 psi, and 31x10.50-15 tire 2.2 cu.ft. (ea.) and start at 15 psi:

1.25*135 + 4*2.2*15 = starting volumes and pressures = 300.75

Now solve for the final pressure after it has equalized in the tank and 4 tires:

P * (1.25 + 4*2.2) = 300.75 = P * 10.05, or P = 29.9 psi

Or for 8 tires:

135+1.25 + 8*2.2*15 = 432.75

P * (1.25 + 8*2.2) = 432.75 = P * 18.85, P = 23 psi.


Basically take whatever size tank you have at whatever pressure and multiply those two numbers. Then multiply the number of tires times the volume of each tire times the starting pressure in the tires and add that product to the first (tank) number. Then add up the total volume of the tank and tires and divide that into the total you calculated and that is the final pressure.

EWAYota

96LtdYota

you people take wheeling to a whole new level... i just bring my little trusty target cig lighter inflator

KING

I was just about to start a thread asking the same question but rather using a 7 gallon air tank from Wal-Mart.

I had a 300 psi air pump powered via the cigarette lighter and it only took two uses for it to burn out. I paid $60 for it at Auto Zone. After the experience I had with this one, I was looking for an alternative to air up tires.

Tell me more about this "trusty target inflator" you use and how much you paid for it and how many psi is the pump rated for?