R4 vs. Turf Tires

[MChalkley]

Something I learned a while back from an engineer who specializes in such things is that the ground pressure exerted by a tire is largely dependent on the air pressure in the tire. So, if they're over-inflated, as is usually the case, the damage will be much more severe.

Mark

 

[W5FL]

Interesting observation. Obviously the weight of the tractor at each tire divided by the sq inches on the ground is the pressure on the ground in psi. To a large extent this is dependent on the pressure in the tire. I believe mine show 18 psi rear and 34 psi front with a tractor weight of 8000#.

From Firestones Web Page: The footprint at no penetration/3 in penetration:

16.9x30 R1 Ag Tread 3750#@18psi 216 sq in/540 sq in
9.5x24 R1 Ag Tread 1870@30psi 79 sq in/245 sq in

Assume reasonably equal loading with loader and all wheels filled with ballast. The loading would be about 1/2 of this without a loader and without ballast.

13.55 psi loading on the grass with no penetration
5.0955 psi loading on the dirt with 3 in penetration

That seems like very little ground loading with an 8000# tractor. It would be interesting to see what it would be at lower inflation pressure but I could not find that data.

I imagine that turfs will come in about the lower value of 5 psi and R4 tread will be somewhere between 5 and 13 psi. Wonder if this loading is pretty constant with different size Kubotas?

Tell JimBinMI that I used EXCEL to do the calculations, but he needs to come over and check them. /w3tcompact/icons/smile.gif

 

[Anonymous Poster]

The average contact pressure on the soil at the tire footprint is always about 1-2 psi more than the inflation pressure in any tire be it radial, bias, R-2, R-4, etc. If the tire were simply a tube (a membrane) the average contact pressure would be the same as the inflation pressure. However, since the tire carcus has some stiffness, the average contact pressure is 1-2 psi higher than the inflation pressure. It is important to use the term "average" because it is not uniform pressure. Under the lugs it is higher and between lugs it is much lower. However, when averaged over the entire footprint area the contact pressure is just a little bit higher than inflation pressure. When comparing two different tires on the same tractor, the important consideration is the inflation pressure required in each tire to support the same axle load. Small volume tires require more inflation pressure than larger volume tires. Comparision of footprint areas from a handbook is not very reliable because the published area is always that area that occurs when the tire is carrying its maximum rated load and inflated to the maximum required pressure. Very few tractor tires operate there. Normally the load and the corresponding pressure would be much lower.

 

[JimBinMI]

Wen,

I won't check you, got better things to do. I'm working on being kinder and gentler with you Orange boys!

And just for the record and you can quote me, IF I could have bought more Kubota for equal or less money I probably would be an Orange owner right now! As is was/is I bought more tractor for less money with similar quality, assembled in the good ole USA and I have a great dealer! Even Steve Carver couldn't believe the prices at my area Kubota dealer!

JimBinMI

We boys and our toys!

 

[W5FL]

Now that is a paradox. A kinder and gentler french blue you. /w3tcompact/icons/smile.gif

Steve couldn't believe the prices were that low or that high at your Kubota Dealer?

What were you doing at a Kubota dealer? Are you secretly negociating to trade up to a Kubota with enough HP to run a tiller????