Tractor, Truck or Car - heaviest per square inch?

Bob_Skurka · Apr 27, 2005

The farmer has been there 100's of years, the new guy say's this is great, now get that farmer out of here! 

Yup that is pretty much the feeling of a lot of city to country folks. I've made no secret about the fact that I am one of the folks who moved out to the country. But the lovely Mrs_Bob and I both decided that if we would move out to some land, then we would also adopt the culture as best we could. There are plenty of folks like me who moved out to the country. And there are plenty like the guy down the road who just can't seem to shake the city attitude.

One nice thing about living in a private neighborhood (28 homes on 155 acres) is that we do have rules. While some folks don't like rules, I love them. Because the rules were there FIRST and then the people moved in and had to sign on the dotted line that they accept the rules. Now we have a great case, a guy doesn't like the rules. But I like the farmer and the farmer is protected by the rules. He needs that easement to access my 32 acre field to farm it. The rules say he can. The guy says (among a list of other complaints) that the farmer is destroying his driveway, which is also the easement. First, even if the farmer was destroying it, it is still his right to use it (although he might have to repair it). Second, this thread gives me enough information to show that the farmer is NOT causing the potholes. The brain trust here on TBN is a wonderful resourse.

Me, I'll just enjoy sitting up on the porch watching the farmer harvest this fall like I always do. And when he harvests soybeans I'll remember to close the windows because the dust off the fields is pretty overwhelming, but hey, that is just one more thing I learned to adapt to when I moved out here. And the roar of the tractor, that just means there is a friend out in my back lot who looks out for me and knows that I will look out for him.

Now the kids who run the 4 wheelers through the lovely Mrs_Bob's flower beds, I can live without them . . . but funny thing, they were not here when we moved here, they came into the neighborhood with one of the city dwelling families who didn't adopt the country ways. Good thing there are more folks like me than like them.

slowzuki · Apr 27, 2005

A point no one mentioned, pot holes are not usually signs of road failure. Potholes are the result of poor draining road material or road crown.

Rubber tired vehicles push a wave of water in front of the tire at high velocity and this picks up material and throws it out of the hole, making it deeper each pass.

More trips = deeper / more potholes. Faster speed = more /deeper. Low speed tractors don't tend to cause potholes at the same rate. In the days of horse drawn wagons, I'm told potholes did not generally occur on gravel roads, only rutting in wet areas.

I'd say the homeowner with his faster vehicles and traversing in wetter weather is mostly responsible.

Charlie_in_TX · Apr 27, 2005

( So what does more harm to the gravel road? Absolute weight or weight PSI? )
Niether, driving on a wet gravel road will do the most damage.

JoeL4330 · Apr 27, 2005

For a pneumatic tire, the psi on the ground is the psi in the tire ...a biggggg truck tire might have 80-100 psi in a tire ...deflate a tire some (as long as the rim doesn't hit ...i.e., still pneumatic) and the psi inside AND outside goes down ...that's why the patch gets bigger ...the area of all the patches, times the psi of the tires equals the weight of the vehicle. This should answer the question as asked ...

But, that's for a smoothly rolling vehicle ...once ruts/holes begin, then the vehicle adds kinetic energy from the bounce and the ruts get worse and worse and worse especially from unsprung undamped vehicles (like farm equipment)

Egon · Apr 27, 2005

You fellows are getting me all confused. /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

My empty P/U has 80 psi in the tires. I put a load of 4000 pounds in the back the tire pressure is still 80 psi.

Now somehow me thinks the psi placed on the road by the loaded truck has gotta be a little higher.

Sure hate to see a 110 pound lady in spike heels walking down that road. The psi would just be outa site! /forums/images/graemlins/grin.gif

Egon

JoeL4330 · Apr 28, 2005

80 psi in the tires, 80 psi bearing on the ground ...load up your pickup, the tire patch increases ...so that the area of the tire patches times the psi of the tires equals the weight of the loaded truck.

"air down" (let some air out) to fewer psi, bigger patch, more flotation, but same rule: patch times psi = weight ...UNTIL you overload and/or air down so the vehicle is sittin' on the rim.

Bob_Skurka · Apr 28, 2005

JoeL . . . I think I get it.

Egon wrote: My empty P/U has 80 psi in the tires. I put a load of 4000 pounds in the back the tire pressure is still 80 psi.

Now somehow me thinks the psi placed on the road by the loaded truck has gotta be a little higher. 

I think I thought that too, but the more I think about the whole PSI issue, and the more I read the Goodyear Tire PDF file that I downloaded, the more the PSI thing makes sense.

BUT, along the lines of Egon's very disturbing mental picture of a Fat Lady in spike heel shoes scenario, I still wonder about the concept of the 10 ton combine with tires filled to 20 psi going over a wooden bridge versus a 20 ton combine with tires filled to 10 psi going over the same bidge. Based on PSI, the lighter combine with higher PSI might break some of the rotted deck boards, but based on total weight, the 20 ton combine will not break the deck boards but will collapse the bridge!

So when does weight do more damage than PSI in the tire?

davido · Apr 28, 2005

I am not an engineer and know little about psi and patch etc. The psi in a tire, however is a measurement of the pressure exerted within the confines of the tire, not a measurement of the pressure exerted by the tire on the ground. I do not see how the pressure exerted by four tires that are not attached to any vehicle could be anywhere near the pressure exerted by the same four tires attached to a 10,000 lb vehicle. While the increased contact area due to the squatting of the tires would help distribute the pressure exerted, clearly the amount of damage or wear by these two scenarios would be grossly different.

It seems that if the psi in the tires is in excess of what it takes to keep the tire inflated and the rim off the ground then increased weight would would increase the pressure exerted on the ground. Then again, what do I know.

Egon · Apr 28, 2005

Okay - so I got enough air in my tires the tire patch don't change?? What then??

Egon /forums/images/graemlins/grin.gif

Highbeam · Apr 28, 2005

Well Bob you and I have different mind's eyes. When I think of a 110 lb gal in spike heels I start hooting and drooling. You think of a bad scene involving a fat lady?

There are many TBN wives, mine included, that would say 110 is not that heavy.

Either way, spiked heels do mucho damage. I have seen hardwood floors with dings in them from the high heels of a 150 lber.

A bulldozer puts down about 3-5 psi. If your two footprints add together to be about a square foot, they should, then your weight is being distributed across 144 square inches. If you weigh 144 lbs then you put down 1 psi just standing there. Great but when you are walking I would venture to say 1/3 of each foot or less is in contact with the ground at any one time. Giving us 3 psi for your foot to fall through the muck. The dozer utilizes mucho tracked surface area to distribute the weight so that the effect on a surface is not much more than a person walking through the area.