Tire Air Pressure

[DenisM]

New to tractors and I had a question about the tire pressure to run in my tires. When I inflate the rear tires, which are 24" R-4's, to the recommended pressure of 20# both tires are cupped so that the centers of the tires hit the ground but not the edges. The fronts do not do this; they had even ground contact across the entire tire.
The cupping is very noticable. On a vehicle this means the tires are way overinflated.
Any ideas, comments or suggestions.

Thanks
Denis

[RoyJackson]

Who recommended 20 PSI? I've got 14-15 PSI in my R-4 tires.
You don't want excessive pressure in the rear tires, Some slippage is necessary for best traction.

[DenisM]

I have a Mahindra 4530 and 20# is the figure recomended in the owner's manual.

[RickB]

Rear tire pressure is dictated far more by the load they cary than what a manual says. As you suspect, your tires are overinflated at 20psi. You can probably drop them down to 10 or 12 and still not get the sides of the tread on the ground. My simple rule of thumb on tractor rears is if they look like they are too soft, they are. A little sidewall flex is not a bad thing; better ride, better traction, less compaction.

[Bird]

Like the other guys said, probably 12 psi would be good. When you said "recommended" air pressure, are you talking about the number of the sidewall of the tire? That's usually the maximum recommended. Another way some use to determine the right pressure is to pour water on a paved surface and drive over it to see what your track looks like when you go from the water to a dry surface. You'd like that track or tread to show all the way across.

[art]

Most industrial tires are leaving our shop at about 10lbs pressure for the rear.

[Farmwithjunk]

Most industrial tires are leaving our shop at about 10lbs pressure for the rear.

AMEN! Personally, I think MOST people run far more pressure in rear tractor tires than is necissary. Ride suffers as well as traction. Most inflation info from tire manufacturers is based on maximum load carrying capacity per tire at a maximum allowable speed. I can't remember ever running more than 15 lbs in any tractor tires and generally around 9 to 12psi. All the R4's on the back hoes belonging to the general contractor I work for are kept at or around 10 to 12psi.

[Egon]

On my Kubota B7100 I've got 15/20 in the rears and 30+ in the fronts.

[3RRL]

On my Kubota B7100 I've got 15/20 in the rears and 30+ in the fronts.

That's exactly what I have Egon, but I vary mine as I need it.
I check the "footprint" on the rears depending what I've got on the back. I need more pressure when carrying a heavy backhoe than with the rotary cutter or even the boxblade on. Then I lessen the pressure in the rears to 10 or 12 sometimes.
I put 30 in the fronts when doing heavy dirt work with the loader, but reduce it to 25 when doing lighter grapple work and even down to 20 when just mowing.

I have a compressor by the tractor so it doesn't take but a minute to set the correct tire pressure ... and check the foot print. I have Ag tires and work on dirt, never on asphalt or concrete. I think that has something to do with it too. Plus it's not like I'm switching all the time either. I'm only at camp on the weekends, so whatever chores I have lasts me that time ... sometimes several weekends in a row. So there is really less changing of tire pressure than my post implies.
But that's what I do.

[jimmysisson]

Without intending to steal the post, how do people check pressure in calcium-filled tires? With the valves as high as possible there's still liquid at them. Seems like they'd spoil the tester. I don't worry about putting live air to the tire, figuring the hose pressure is greater than the tube pressure, but how do you test? My old farming neighbor used to like to see the outside end bars of the ag tread just touching flat ground.
Jim