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Seems like all I can ever find on the tires is "do not exceed XXpsi when setting rim" but nothing about how many psi the tire is supposed to have. Car tires are the same way. "Max air pressure" never operating pressure targets.  And all the pressure text is in super tiny fonts. "Gotta look in the book".

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That's the method I use. Change cores every 2 years. Think I need to make it annual. Last few times (3 units) had to dig out part of the old core.

That's how I do it. WD,220,8070  Not hard,just takes time and not that much. Have to jack each side and takes some jacking on 8070 with squatted radials. Must be held up as I had to remove water valve to get all the old core out. I have a couple spares so I plugged rushing air but you lose a lot of air removing water valve. It works for me. Just pull the cap and see if it's wet inside....time to change.

For the tractors, "gotta lookin the book" is good advice but most of the old tractors ran about 12 PSI in the rears.

As far as cars and trucks, for many, many years the recommended PSI is shown on a decal on the driver's side door column. May even be a federal requirement.

So the thing about pneumatic tires, is that the more weight you put on one, the more the tire squats.  What's happening, is more tire surface is contacting the ground.

A tire with 2000lbs on it, with 10psi, will have a surface contact area of 2000/10=200 square inches. If the tire contact was a perfect rectangle (it's not), it'd be 16" wide by 12" long.  IF you double the pressure (20psi), you'll decrease that contact surface to 100 square inches, which comes out to about 10x10" contact.

Caveat here- This all holds true if the tire contact surface is totally flat (it's not... it's usually a chevron-type tread), and the ground is totally flat (it's not... we're on soil, not pavement).  The result, is that the tread high spots create a higher surface pressure, and compact the soil in... until the composite support of the tread high spots, and the low spots (where the tire has sunk to) equate to the total support load.

Now, in motion, there's a bit of dynamic load that occurs... bouncing, and deforming to suit an uneven surface.  Driving over a laid-over fencepost, for example.  The tire deforms going over that shape, and while it happens, the tire's internal pressure rises a little... the air is being compressed.

When you have FLUID in the tire, it's a different story... because the fluid is NOT compressible.  If the tire is totally full of fluid, it cannot deform in the same way as if it was fully pneumatic.  Not only do you have more weight, you have a tire which might as well be solid... and this makes the tire incapable of doing the deformation-distribution that it would have on compactable soils. 

If you look at the tractive effort demonstrations during the timeframe of the Allis WC's introduction, there was considerable comparison between tractive effort of a spade-tread steel wheel, against a pneumatic tire.  Most were convinced that the steel spades could not be beaten by a rubber pneumatic tire, but in fact, the pneumatic rubber tire's effective drawbar output was HIGHER, because it could deform to increase and distribute tractive effort over soft surfaces, where a solid wheel required extra horsepower just to climb itself out of the hole it was in.

When you fill the tire with fluid, you DO increase the ground contact weight, and you DO increase the amount of total machine load over driven wheels, but you WILL lose the deforming capacity advantage of a pneumatic tire....

And this is ONE of the reasons why manufacturers recommend that you not fill beyond a certain point.

It is also part of the reason why you won't find a sidewall pressure rating other than 'not to exceed when mounting'... because tire pressure IN USE, is determined by field and operating circumstances, not by the road/load circumstances you find on an automobile or highway truck application.  Road tires are load rated because the tire's pressure has a direct impact on how much heat the tire generates internally, and at what loadpoint it will no longer be able to survive safely.  This circumstance doesn't happen in an agricultural field tire, and the agricultural circumstances don't occur on a road tire.

It is important to understand that when you hit a bump with a tire, the tire deforms, and pressure inside the tire rises.  The volume of air in the tire acts as a 'buffer' to distribute this pressure rise, but when that volume is replaced with a liquid (non-compressible), the buffer volume is smaller, so the pressure RISE is much higher, in a shorter time.  This means a good bump could cause a tire or rim to fail... and that's where the air volume LEFT in the tire becomes important... keep the pressure there low, and you'll have better shock absorption... just need enough pressure to keep it from unseating... or if you have tubes, enough to keep the tire and tube from slipping inside the rim.

I replace mine every spring, aren't used in the winter, in the fall I park them in the shed, rotate each tire so the stem is on the top then replace the cores each spring before I move them.  The show girls get blocks under them to keep the tires off the floor.

Put new tires, tubes and rims on the WD45 over 20 years ago, calcium chloride for ballast and they haven't rotted off yet, don't rekon they will in my lifetime.  Also have a little farmall with CC in the rears, been there over 50 years and still in good shape.  Just like anything, knowledge and good practices goes a long way toward production.

And you won’t pull squat.  

Adding calcium chloride to the water DOES increase the weight, AND DOES lower the temperature at which the fluid will freeze.  The density of saltwater is greater than fresh, which is why we float very well in the Great Salt Lake, but not so well in the city pool.  It also does some very unexpected things to submarines that venture into certain waterways in certain parts of the world where salinity is unexpectedly low... or high...

Calcium inside a tubeless assembly will cause significant wheelrot.  (That's a new word I just added to Webster's)... 

A tire/wheel assembly that uses innertubes, will see significantly less circumstance of wheelrot... so long as the tube keeps the caustic contents on it's inner-side, rather than leaking THROUGH it's rubber skin, and... as long as the valve stem and stem adapter maintain a positive seal.  Frequently, you'll find wheelrot greatest around the stem area FIRST, because *unlike Walt*, most people add caustic contents and walk away for three-to-five decades... and those contents become casually migratory.

windshield washer fluid (methanol and water) will usually reduce the freezing point... methanol has it's own interaction with rubber, but it works...  On my little loader tractors, I lay the wheel/tire flat on the ground, unseat the top bead, stick a wedge in it, and pour in Propylene Glycol (pink RV anti-freeze).  It too, has a LOWER density than fresh water, but it needs to be around -25 before it assumes crystalline structure... and I leave plenty of space for air, as my lower back does NOT take the kind of beating the little buggers can dish out when workin' the bucket.

Two important notes about using liquid ballast in tires, rather than iron:

Iron weights in the middle of the wheels have POLAR INERTIA... it takes force to get them spinning, and once spinning, they don't like to stop.  When you use fluid in a tire, the tire can spin up rapidly, and the fluid in side doesn't HAVE to. 

Iron weights have their mass centered on the axis of the tire/wheel assembly... because they're mounted in the middle.  Fluid in a tire... when it's half full... puts that ballast's weight BELOW the axle centerline....

That means the center-of-gravity of the MACHINE is effectively LOWERED by adding that ballast... it'd be the same as having those iron weights always sitting ON the contact point of the tire, not 30" up off the ground.  Imagine having all your suitcase weights suspended below the tractor, an inch off the ground, how much lower the composite center of gravity would be... and how much that would reduce the tipover angle...