Tires Ground pressure

[mgoss77]

Does anyone know if john deere publishes any information about the ground pressure of their 3000 or 4000 series. I'd like to figure it out. We have a farm where we need very narrow tractors and tires but it results in ruts. We have a 3520 with ag tires and i would be curious what the differene between ag tires and r4 tires is. I could try to figure out by measuring how much tread is on the ground and the weight of the tractor, but it also depends on the weight on each axle and how soft the ground is.

 

[beenthere]

I'd think Deere would also have a difficult time sorting out all the variables too, but think your idea of "tread footprint" and weight would be the best and easiest.
Ground softness wouldn't change the pressure (seems to me) but would have an effect on the rutting.
I find R-4 tires leave much less rutting, but then they are much wider as well. Less traction that ag tires.

 

[PioneerMan]

I don't think Deere publishes that. I would look online for generic tread contact percentages, should be able to find that. Then measure, or calculate total tread area and divide tractor weight by. So, for example, a turf tire of total contact area of 40 square inches, with 80% contact would be 32 sq in. If a 3x20 weighs 3200, that would be 100 lbs/sq in. Those numbers are not actual, and I think in reality it is a lot less than that. Make sure to use actual tractor weight. Published weight is usually without loader, weights, load if any, operator, fluids maybe, etc.

Airing down helps increase the total footprint, lowering the pressure applied to the ground. But I don't know if there is a formula for the ratio of tire psi to contact area, I can't think of one.

Good luck...

 

[PioneerMan]

There is good info on tires here. I think someone posted a very good tire primer with lots of stats, you may want to search for it...

 

[Zebrafive]

I don't think Deere publishes that. I would look online for generic tread contact percentages, should be able to find that. Then measure, or calculate total tread area and divide tractor weight by. So, for example, a turf tire of total contact area of 40 square inches, with 80% contact would be 32 sq in. If a 3x20 weighs 3200, that would be 100 lbs/sq in. Those numbers are not actual, and I think in reality it is a lot less than that. Make sure to use actual tractor weight. Published weight is usually without loader, weights, load if any, operator, fluids maybe, etc.

Airing down helps increase the total footprint, lowering the pressure applied to the ground. But I don't know if there is a formula for the ratio of tire psi to contact area, I can't think of one.

Good luck...

I think you have the right idea. Tractor weight/ Contact area. If you know the weight of the tractor and precentage front and rear. You will then be able figure out how much weight is on each tire. Check the air pressure in each tire. Divide that into the weight at each wheel and that will tell you how large the contact area is in square inches. Or easier yet, the tire air pressure is contact pressure in pounds/square inch.

 

[PioneerMan]

I have heard before that psi equals contact pressure but I have trouble believing it. Say a small car and a large truck air the tires down to 10 psi. Are both putting down 10psi of pressure on the ground? I believe it is tire pressure, unrelated to ground pressure., but I could be wrong.