Ground pressure

[Hambone]

How do you figure accurate ground pressure?
Total weight divided by square inches of tire contact??


Thanks!

 

[tc35dforme]

Sounds good to me. Figuring the actual contact patch of a tire could be tricky. On hard soil, the tire will sit up with less tread contacting the soil, so higher PSI. On mush, the tire will sink exposing a greater surface to the soil.

 

[bigpete]

That's the basic premise. If you really want to impress the tractor-geek groupie babes out there (they are out there, you know...), you would need to calculate the lbs. PSI for each axle considering total weight distribution. You might even want to do so with loader and implements on and off! /forums/images/graemlins/smile.gif

 

[normde2001]

I'm racking my brain trying to figure out what a person can do, armed with this information. /forums/images/graemlins/confused.gif

 

[bigpete]

<font color="blue"> "...impress the tractor-geek groupie babes out there (they are out there, you know...)" </font> /forums/images/graemlins/grin.gif

 

[slowrev]

Not sure what to do with it either, maybe it has to do with the guy that was trying to plow snow on the frozen pond ?

The only valid thing I can think of is for figuring strength for trailer decking boards or something like that.

 

[Hambone]

Okay, I will come clean.
We need to run a truck in a residential neighborhood. They said we could not run a tandem axle truck, Had to run a single axle.
So, I am trying to make a case that ground pressure is less with a tandem truck versus a single axle.

 

[tc35dforme]

That's weird /forums/images/graemlins/crazy.gif, usually they want as many wheels on the pavement as possible to minimize the damage to the pavement. That's why they have the dumps with the retractable third axle and the cement trucks with the fold -down extra axles.

Is it one of those neighborhoods where you have to mow your lawn in a certain way or the 'owner's association' won't invite you to the Saturday night social ??

 

[zuiko]

It is, that is the whole point of adding dual wheels and additional axles to heavy trailers. Another set of wheels will cut the pressure in half if the load remains constant and the wheels are the same size. Good luck.

 

[keeney]

I don't think the mushiness of the ground is taken into account in the ground-pressure rating. Otherwise, all the numbers would be artificially lowered.

I think the only thing you can use is the tire contact patch area on a hard, flat surface at the lowest recommended tire inflation pressure for the given application.

- Rick

 

[CTyler]

</font><font color="blue" class="small">( Is it one of those neighborhoods where you have to mow your lawn in a certain way or the 'owner's association' won't invite you to the Saturday night social ??
)</font>

Don't forget the roller to make it lay the pattern correctly.

 

[Renze]

Yes, many people with little knowledge have different wishes...

At the park my brother lives, the owners association allows a 6x6 dump truck with rigid tandem on their asphalt roads, but not a tractor and 18 ton dumper on a steered tandem with flotation tires. The tractor and dumptrailer have a lower ground pressure and have less sideway friction (when turning)than a rigid tandem, but because it looks bigger, they dont want it..

My brother has to fool them with similar discussions, ground pressure, sideway friction of tandems, to get construction transport near his house... What arguments he uses in the discussion, depends on what transport he needs to get allowed... /forums/images/graemlins/grin.gif

 

[Hambone]

That is exactly what I said. That is what we also do. But, trying to convince will take some actual facts, to them this is hearsay.
I guess they want it in writing from some expert??
Pretty aggravating. So tomorrow I will be traveling 5 1/2 hours one way to get another truck from another division. Such a waste of time and money, unless of course I am wrong about the pressure.

 

[keeney]

Its probably more of a total weight thing. A Dual-Aale truck or trailer will have a lot more total weight than a single-axle.

Most road restrictions are like 7 or 9 tons "per-axle", though, so this doesn't make a lot of sense.

- Rick

 

[timb]

Hmm. To avoid too much tractor-geek status I guess I shouldn't post the spreadsheet I did at one time comparing ground pressure between the old tractors I know and various sized of modern CUTs and utility tractors. /forums/images/graemlins/tongue.gif

I wanted to know how much worse (or better) the ground pressure would be (which is after all the best indicator of potential rut "damage" to the lawn/ground) from what I was used to with the existing equipment.

But I had to guesstimate the contact patch area - never found anywhere that published that spec.

Tim

 

[normde2001]

Talk about ground pressure, I can recall when all farm tractors had iron wheels, and those iron cleats caused some monstrous ground pressure in the asphalt when a farmer would venture onto the highway. /forums/images/graemlins/frown.gif

 

[bigpete]

timb, Absolutely no offense intended. In fact, I consider myself to be a major tractor geek. Self-effacing humor, you know...

I, for one, would like to see your spreadsheet.

 

[Soundguy]

I work alot with the county and DOT road depts ( civil eng... ).. here's there take on this...

They have to categroically deny a vehicle.. that is by class.. not case by case basis. The more axles a truck/trailer has.. the heavier it can be. By saying one rear rigid axle.. they have pretty much limited that road to 26000 pound vehicles.

Otherwise, a semi, with an over dimensional permit and a 50 ton flatbed could roll in with 6 axles, and carry a 112000 pound piece of equipment...

Thos signs are probably like ours that show a picture of a moving van ( uhaul ) and say.. local deliveries only.. or frontage streets only.. etc.

Soundguy

 

[wayneg]

I believe the ground pressure, in terms of force per unit area, will be equal to the tire pressure. This is where the forces will be in equilibrium.

In other words, a tire pressure of 30 psi will have a ground force of 30 psi. The contact area will then be a function of the weight on the tire divided by the tire pressure.

 

[jmc]

Wayneg,

By that logic, the more air you put in your tires, the more your tires sink in.

I think your theory is true if the only source of tire pressure is the vehicle weight. But that only accounts part of the total tire pressure. Most of it is from the air hose, as a preload to keep the tire in a useful shape.

John