Loaded-tires-air pressure?

[Henro]

Gamemaster,

Everything I have read regarding liquid fill in tires said for maximum level to have the valve stem at 12 O'clock and fill to the level of the valve stem, and no more.

When I filled my rear tires, I put the valve at 12 O'clock and lifted the back of the tractor so the tires were just off the ground, and pumped the liquid in.

I had to stop several times to release air pressure, as the liquid going into the tire displaced air, and the air pressure in the tire increased as the result.

The final step was to let tire pressure go down to zero at the finish. At this time the tire was over filled with fluid, and the fluid was blown out before the air finally started coming out.

When I saw (I used clear plastic hose) that it was all air, with just a bubble of fluid now and then coming out the fill hose, I knew the liquid level was at the prescribed fill level of the valve stem with it was at 12 O'clock.

Here is one caution. Some rims do not have a lip on the inside to hold the tire on if air pressure goes to zero. If you want to lift the tractor wheel off the ground and see if liquid will come out of the valve stem, when it is at 12 O'clock, you may want to be careful, and if necessary, stop and put air pressure back in the tire, then continue to drain fluid out in a drain, repressurize, drain sequence if needed.

As far as when to check tire pressure. I know that some members with far more experience than I have recommend lifting the tractor off the ground before checking pressure in loaded tires. It is hard for me to understand what would be gained in the long run by doing this. I don't do it. I don't see the need myself.

Here is the reason. I prefer to look at my tires, or feel the way they ride and adjust tire pressure accordingly. Now if someone told me I had to fill my tires to a certain pressure, and that pressure was what would be in the tire when the tire was not supporting the tractor, I would have no option but to lift the tire off the ground before measuring what pressure was in it.

But since no one is telling me what my tire pressure has to be, I choose to determine what the pressure in the tire should measure when the tire is on the ground. I think I run about 12 psi normall, but I can tell you last spring, the tires looked a little soft, and measured 4 psi! /forums/images/graemlins/blush.gif Guess I had not checked them for a while! /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif

Now I would be willing to be that once tire pressure is set to some value when the tire is off the ground, that after the tractor was set back on the ground, if the pressure was measured again (probably a little higher now) and recorded, that it would no longer be necessary to check air pressure with the tractor in the air. Simply setting pressure to the higher recorded value would put the "in the air pressure" pretty much dead on.

Boy, that's a lot of words to say, my guess is that your guess is correct. I would as I mentioned above, not let the tire pressure drop to zero though, just incase you have one of those rims that the tire can fall off of. That would make a simple job a real pain, as someone here has posted previously...(Forget who, glad it wasn't me...)

 

[alexinPA]

Very interesting discussion, but nobody except Henro gave a direct answer. What is the loaded tire air pressure should be?
Say, relative to max pressure indicated on the tires? Anybody cares to share this secret?

 

[RoyJackson]

</font><font color="blue" class="small">( Very interesting discussion, but nobody except Henro gave a direct answer. What is the loaded tire air pressure should be?
Say, relative to max pressure indicated on the tires? Anybody cares to share this secret? )</font>


I keep my rear tires at about 15 PSI. I keep the front tires at 20 PSI and increase as required for FEL work.

 

[patrickg]

Something sounds wrong... I can't believe that the instructons would say to fill the tires to the valve stem with the stem at tha 12 o'clock position. The Kubota manual I read says 75% max fill. This would be closer to the 9 O'clock position than 12.
/forums/images/graemlins/confused.gif Pat /forums/images/graemlins/confused.gif

 

[wd45]

The max. pressure should be on the tire. In a lotta years of farming I remember only filling our tires to about seventy five percent liquid, you could go higher I guess, but you would increase your center of gravity also. I never remember raising a tire off the ground to measure the pressure, can't think of any reason to do so. We all do things out of habbit, so just because we didn't do it doesn't mean that's the right way. If I wanted to increase the weight of the tractor above the weight of 75% filled tires, I think I would hang weights on the front or back, the lower the better.

Mike

 

[_RaT_]

I'm pretty sure my rear tires do not indicate a working pressure on them as it depends on the load and the speed. Your manual will state what it should be. My rears do indicate a maximum PSI for seating the tires. I try to put the least amount of air in the rears and not have them pop the bead. Mine are at about 12 PSI and I do not ballast them. I use a low pressure gauge. I think max pressure it reads is 20 PSI.

 

[willfick]

Nine o'clock is half-way up the side; that would be fifty percent. Ten-thirty isn't enough either, since the surface of the fluid will be horizontal rather than pointing at 45 degrees like the hour hand of a clock.Since no one can be expected to be able to easily see where 75% is most instructions use the "up to the stem with the stem at 12:00" as a rough measure. In addition to leaving enough air for bounce the reason for that is stability at speed. What you want is for the fluid to be able to start following the rotation of the tire as soon as the tire starts turning. The faster it turns the more fluid flows over the top of the rim. What you want to avoid is a partially filled tire that becomes more and more unbalanced as it goes faster and faster, and that, if you put on brakes hard, can do all manner of unpleasant.
As to the pressure needed, it's about the same whether the tires are loaded or not. No psi number will be right for all machines. The best rule of thumb I've heard, and this from more than one experienced operator, is that on hard ground the outside end of the tread bar should be just touching the ground.
Wm

 

[Bird]

William, what you say about imbalance as you increase speed, or the results of a sudden stop, certainly make sense; however, I wonder if the speed required to cause those results isn't more than the top speed of most, if not all, tractors. I filled the rear tires on my B2710 to the level obtained with the valve stem in the 12 o'clock position. And I was never able to tell any difference at all in handling, stopping, etc., even when the made the occasional 7.75 mile trip on a paved (asphalt) road to my brother's place. Of course the top speed on the B2710 was 11.9 MPH.

As for what you say about the air pressure, outside end of the tread bar touching, etc. is what I also consider the best way to determine the best air pressure. I've seen some written instructions to drive through a puddle or set spot and then onto dry, flat pavement to look at the tread pattern for just that purpose.

I ran 12 psi in the rear tires on the B2710, while a farmer neighbor with big Deeres, two of which he put duals on the rear when plowing, said he ran 10 psi in his.

 

[rozett]

I was led to believe that if you fill it up to just cover the rim, you will be close enough to 75%.

 

[willfick]

I'd say that having filled them properly you avoided the bad effects. Also, I'm sure you're right about some tractors' never going fast enough to matter.
One like my old Farmall H, on the other hand, a narrow front model with 11.2-38's on the back and capable of making near 17mph with a good tail wind....... /forums/images/graemlins/cool.gif