Deuce ground contact pressure

[Tascabe]

OK - having searched this site, manuals and the web and not finding the answer - I am posting in hopes that somebody has the answer before I have to start doing math

I am trying to find the approximate ground contact pressure of an M35A2 with Stock NDT 900X20 tires at the proper road tire pressure of 50psi.

It seems that some of the folks on my road want to raise a stink claiming that my Deuces tear up the gravel road - even though I do not even drive them very often

I want to go back at them with some facts and figures.

I have found formulas to figure this but my math skills are rusty.

I have found some info about the Dodge 5/4 pickup and the 5 tons but not for Deuces.

Does anybody just happen to have this info?

Thanks in advance

 

[Dumpster]

contact pressure

We'll, it's really quite simple.

On an inflated tire, the air pressure in the tire is the contact pressure. With lower tire pressures (IE 15 psi mud & sand) the contact patch on the tire increases resulting in a larger footprint for the tire. At higher pressures the contact patch decreases resulting in less tire area holding up the same amount of weight ( IE 55 psi paved road). Higher tire pressures result in less tire on the road for a given weight resulting in higher ground contact pressures.

an F-250 pickup with 85 psi tires results in higher contact pressures than a 5 ton with 55 psi.

Hope this helps

 

[saddamsnightmare]

May 25th, 2010.

Toscabe:

The other way to figure it out, is that a stock empty WO/W deuce weighs about 13,500 lbs divided by 10 tires in contact with the ground.... Approximate weight is 1350 lbs per tire, divided by 50 lbs tire pressure gives us 27 square inches per tire ground contact....per tire.
Most automobiles and smaller trucks place their weight on four contact points about the size of the palm of your hand in area.... An F250/F350 will have more ground contact pressure on fewer square inches of contact surface. I've had a Dodge 2500 FWD sink far enough here in Texas grass and mud after a rain to need a Ddeuce to pull it out, and the deuce never tears the ground up the way the pickups do.... they leave ruts 6 to 9+ inches deep, versus the deuces 2 or 3" ruts....
Purely empirical, but proveable. Try it some wet day....

 

[Tascabe]

Really that simple huh?

I guess all the formulas I found just had me thinking it was so much more complicated.

But that makes sense I guess.

I knew that the overall pressure would be less than you would think looking at them since all that weight is on 10 large tires but could not figure out how to get the figures.

Found a marine amphibious landing manual that listed the Dodge 5/4 pickup at 10.7psi or 6.1psi depending on its "mobility" rating and the 5 tons at 18.03psi for the front tires and 10.30psi for the rear tires.

 

[Flyingvan911]

Go to a truck scale and weight your deuce. It will only cost 10 bucks or so. You'll get the weight on the front tires (divide by 2). You'll get the weight on the rear tires (divide by . The front tires will each have more weight than each of the back tires. Good luck.

 

[wreckerman893]

Your neighbors are either (A) misinformed (B) clueless (C) just can't stand to see somebody else having a good time with their chosen vehicle.

A large twin axle motor home will put more ground pressure on a road than an empty deuce.

I have seen idiots in 4 wheel drive pickups do far more damage to a dirt road than my deuce ever will.

Unless there is a low weight bridge on that road they have no reason to complain....your taxes pay for that road just like theirs do.

Tell them to go pound sand (in a nice way of course).

 

[militarysteel]

well the front tires alone carry lots of lbs... the engine alone is 3500, plus everything else... sitting right on those front 2 tires. divide that by 2.

 

[cranetruck]

well the front tires alone carry lots of lbs... the engine alone is 3500, plus everything else... sitting right on those front 2 tires. divide that by 2.

That's where 4 front tires have an advantage...
In the image below, the depression in the snow was equal or less than my own foot prints.

 

[hoop]

I do not see contact pressure as being the problem.
If the drive is straight and dry, there will be little to no damage.
But if there are turns and wet and not enough "base" I think it might leave ruts.
I believe the ruts and or loosening of the gravel base will come from "scrubbing" effect not the "contact pressure".

 

[Tascabe]

Well - it is a "Private" road - we all pay into a fund to maintain it.


Problem is that this fall/early winter was wet and part of the road is on top of solid granite - so it heaved when it froze.

Mind you - I did not drive my trucks on it until after it heaved and only once - so it was not from me anyway. Adn in fact - I flattened out a few heaved spots with it.

Mostly I think they want to start drama - they are known for this.

It is a 15mph road anyway and I drive that or slower in the Deuces.

There are some curves (road is ~1.5 miles to my house) but my house is second to last and the last half of the road is fine with no signs of any heaving or anything - so that kind of proves my trucks have littel to nothing to do with problems at the first half of it.

I am not sure facts would do any good anyway - but I will try and teach them something.

And I think wreckerman hit it on the head - they are all 3

Wait until I get more Russian trucks If they think the Deuce is big - they have not seen a URAL 4320 yet!! Or a BRDM-2

 

[stumps]

The average pressure your tires put on the ground is slightly more than the air pressure in the tire. The casing has some capability to remain round even without internal pressure, so that will add to the ground pressure. And, the tire's lugs are quite hard rubber, so they will apply significantly higher pressure to the ground than the air pressure in the tire. That is why they imprint themselves in the ground, and give you traction.

That said, the ground contact pressure of your deuce is quite a bit less than most 3/4 T PU trucks. PU trucks typically run with 60 to 80 PSI in the tires. The per tire weight is comparable. An empty F250 with 4WD is around 5000 lbs, so it puts about 1250 lbs force per tire on the ground. An empty deuce weighs about 13,500 lbs, so it puts about 1350 lbs force per tire on the ground. Fully loaded, the F250 would put 2150 lbs force per tire on the ground. Fully loaded the deuce would put 2350 lbs force per tire on the ground.

Notice I always say PSI when I mean pressure, and force when I mean weight. They are not the same thing at all. PSI are pounds per square inch. That means that if you divided the tire foot print into 1 inch x 1 inch squares, each square would put about the 50 lbs force on the ground with a normally inflated deuce tire. Force is what makes bridges fall, and PSI is what puts ruts in the road.

-Chuck

 

[zout]

How any of your neighbors that access that private road own cars - suv's and pickups.

If they carry home more weight than allowed per axle they will be putting more surface weight per wheel than you are. Put that 10 bags of landscape marble rock in the truck - it fits - same as that bucket full of gravel to repair a driveway that gets loaded in the back of a pickup.

You have seen then elsewhere - pickup box loaded full and front end of the truck high in the air - that is what also adds to road surface getting destroyed.

Fill the back of your car with about 6 bags of cement 80 lbs each and weigh the patch surface.

Just because you have that big truck and tire's that look like you could grind up rocks with them - does not mean much unless you start to distribute weight in it that is not equal per axle.