Tire pressure

[dryfly2u]

Just bought new kubota 7800.
Back tires have liquid, was wondering what pressure to run in tires, they seem alittle hard now the ride is rough, wondering if softening them up alittle would help. How low can u go without spinning the tire on the rim.

 

[Bird]

Which tires do you have? R1, R4, turf? One way is to drive it through a wet spot onto dry level concrete and see what kind of "footprint" you get. You'd like the tread to contact the ground all the way across. On my B2710 with R1 tires, that was about 10-12 psi.

 

[bnixon]

Hey Bird,

This brings up a question I have....

I put my guage on my rears the other day and water started dripping out of the guage. Is there a special guage for checking filled tires? will the water hurt the air gauge?

I had the valve stem pointing up. I guess this is how you are suppose to check them? It made since to me anyway?

thanks,

 

[Casimir]

I'm not Bird, but I am just about as old, and retiring this week, so there is some similarity /forums/images/graemlins/grin.gif.

Your valve stem should be at the top of the wheel when you check the air pressure, so that the other end opens into the air pocket above the fluid. If you get fluid out of the valve stem in this position, you probably have too much liquid in your tires. I think the rule of thumb is 75% or just below the top of the rim for fluid, and air the rest of the way.

 

[Bird]

</font><font color="blue" class="small">( Is there a special guage for checking filled tires )</font>

Yes, there are air/liquid gauges for filled tires. You can probably get one at most auto parts stores as well as tractor places. They don't look much different, nor cost much different, than a regular air gauge.

</font><font color="blue" class="small">( will the water hurt the air gauge? )</font>

If it was just water, probably not, at least if you got all the water out of it. If you have calcium, or if you leave water in it, it may rust.

I agree with Casimir; I always tried to check the tire pressure with the valve stem at the top (12 o'clock), and in my case, I always had the air hose handy, so I'd give it just a quick shot of air before I put the gauge on just to blow any moisture out of the valve stem.

 

[chim]

I have a 7500 with R4's and run 15 gallons of antifreeze mix in the rear tires. The R4's are fairly hard tires, and last Summer I dropped the pressure till I ran into trouble. That happened at 7PSI. At 10 or 12PSI, I haven't had any problems. If you ran R4's at the max pressure you may as well use wooden wheels.

As you might already know, the liquid load shouldn't exceed 75% of the space...................chim

 

[Anonymous Poster]

Hi,

I've run my WW fluid filled rear tires on the back of my Kubota B2910 at 12 psi for almost a year now without problems...backhoe and loader work mostly, but other things as well such as mowing with the RFM...

 

[chrisjbell]

If the valve stem was pointing up you shouldn't get water out of it. Bird's suggestion to shoot a bit of air into it before checking is a good one - if you do that, the stem is "up", and get liquid then you have too much in the tire. Point the valve stem to about the 10 or 2 o'clock position and drain it until you get just air. Then pump it back up - 10 to 15 PSI seems to be a good number (at least for R4s). You don't want to have the tire filled much above the axle or else you are actually raising the center of gravity. 75% is about right.

 

[RickB]

Adjusting liquid fill level.

For maximum ballast, use 11:00 or 1:00. Do this proceedure with the wheel jacked up, or you will displace too much liquid as the tire collapses on the bottom from the weight of the tractor. There is nothing wrong with tires loaded to "rim height" That has been commonly accepted practice in the Ag world since tires have been fluid-filled. Don't drain CaCL solution where it will do damage.

 

[chrisjbell]

Re: Adjusting liquid fill level.

<font color="blue"> For maximum ballast, use 11:00 or 1:00. </font>

That'll certainly maximize the weight of the tire but I've heard some say that filling too much above the centerline of the wheel raises the tractor's center of gravity. I guess if you're going for max. weight (as in most agricultural applications like row farming) you'd want to do that. For me, on my hills, I want to make the tractor as stable as I can so I don't fill too far, keeping the COG as low as possible.

 

[Anonymous Poster]

Re: Adjusting liquid fill level.

<font color="blue">... but I've heard some say that filling too much above the centerline of the wheel raises the tractor's center of gravity. </font>

It's highly unlikely that ballast added to tires could raise the tractor's center of gravity. The center of gravity of the tractor is certainly above the tractor's axles. A totally filled tire would have its own center of gravity at the axle center... it could not raise the center of gravity of the tractor, unless the center of gravity was below the axle to begin with.

The net affect of filling the tires less than totally full will tend to reduce the center of gravity of the tractor/tire combination [more than a nearly full tire will]. But sloshing needs to be considered. Should a tractor with half-filled rear tires get into trouble, it is possible that the liquid in the bottom half of the tire could slosh up to the top half of the tire..with the net result being that, rather than helping to lower the center of gravity, the liquid actually raises the center of gravity of the tractor during the crisis...

I don't know if this is a real concern or not. I think I read somewhere that it was...or might be. Or maybe I just read that half-filled tires and sloshing can cause problems when running at higher speeds on roads...???

Anyway, I just filled my tires with the valve stem at 12 o'clock...seems to work just fine. There seems to still be enough air in there to give some cushion...

 

[chrisjbell]

Re: Adjusting liquid fill level.

<font color="blue"> Anyway, I just filled my tires with the valve stem at 12 o'clock...seems to work just fine. There seems to still be enough air in there to give some cushion...
</font>

That is exactly what I did when I first filled them - and then I dumped some of the liquid out after reading that they shouldn't be that full /forums/images/graemlins/crazy.gif.

I'm not sure how much of a difference it really makes - I actually went a while with one rear tire filled and the other empty after getting it fixed. It didn't seem to make a huge difference, but I doubt that is a good idea /forums/images/graemlins/blush.gif. But I keep 'em filled up to about 75% - 80% and that seems OK. I'm certainly not the end all expert on the subject, though /forums/images/graemlins/wink.gif.