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Unread 03-11-2013, 06:32 AM   #31
Ross
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Quote:
Originally Posted by wilson1010 View Post
And this is the reason that one cannot handle any increased amount of weight simply by increasing tire pressure.
More tires can handle more weight. Skinny versus fat depends on the rim. Look at vehicles designed to carry heavy loads. The tires are not much wider like the rims.
The issue is the proper tire with proper rim, on properly equipped vehicles. Vehicles designed to carry heavier load have more tires, not fatter tires, unless they have fatter rims. The setup for heavy weight is not the same as we set-up for off road.

This is a pic of a Heavy Equipment Transport (HET), its load weights over 60 tons. See how many tires. Se how wide the rim is compared to the tire:


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Unread 03-11-2013, 07:18 AM   #32
wilson1010
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Quote:
Originally Posted by Ross View Post
More tires can handle more weight. Skinny versus fat depends on the rim. Look at vehicles designed to carry heavy loads. The tires are not much wider like the rims.
The issue is the proper tire with proper rim, on properly equipped vehicles. Vehicles designed to carry heavier load have more tires, not fatter tires, unless they have fatter rims. The setup for heavy weight is not the same as we set-up for off road.
Agree. More tires more weight. More tires, more contact area. more contact area, lower pressure per tire. Formula= weight of rig/tire pressure in psi/number of tires= contact area per tire.

The maximum load limit of a tire takes into account the maximum safe contact area. Hence, when the maximum safe contact are is reached, one must get a bigger, higher rated tire, or as above, a whole lot of tires.
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Unread 03-11-2013, 07:51 AM   #33
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Originally Posted by MPond View Post
While thatís an interesting argument, itís incorrect. Your theory treats the tire like a balloon, and ignores the fact that tires are rigid and have a structure of their own. While the load on the tire and the inflation pressure do play opposing roles in how large the contact patch is, neither of those properties is linearly proportional to the size of the contact patch, or to each other. A 10% increase in load or a 10% decrease in tire pressure does not equate to a 10% increase in the contact patch. And comparable changes will not offset each other. While the load and PSI can be changed at will, the contact patch will always be limited by the tire geometry.

If you want to see some examples of this, take a look at this article: http://www.performancesimulations.co...on-tires-1.htm

It explores this specific argument, and analyzes the formula that Wilson is proposing: Contact_patch_area = Weight / Tire_pressure

Though not conclusive, it does provide some interesting evidence that there are many other forces as work dictating contact patch, and the wider tires tended to have the larger contact patch, everything else being equal.
This! Thanks for injecting some reason into this trainwreck of a thread
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Unread 03-11-2013, 08:05 AM   #34
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Originally Posted by wolfcreek View Post
This! Thanks for injecting some reason into this trainwreck of a thread
Quote:
Originally Posted by MPond View Post
While that’s an interesting argument, it’s incorrect. Your theory treats the tire like a balloon, and ignores the fact that tires are rigid and have a structure of their own. While the load on the tire and the inflation pressure do play opposing roles in how large the contact patch is, neither of those properties is linearly proportional to the size of the contact patch, or to each other. A 10% increase in load or a 10% decrease in tire pressure does not equate to a 10% increase in the contact patch. And comparable changes will not offset each other. While the load and PSI can be changed at will, the contact patch will always be limited by the tire geometry.

If you want to see some examples of this, take a look at this article: http://www.performancesimulations.co...on-tires-1.htm

It explores this specific argument, and analyzes the formula that Wilson is proposing: Contact_patch_area = Weight / Tire_pressure

Though not conclusive, it does provide some interesting evidence that there are many other forces as work dictating contact patch, and the wider tires tended to have the larger contact patch, everything else being equal.
What is interesting is that Pond, has done the classic mistake of novice Internet users.

He has assumed something to be true because he saw it on the Internet.

Just what reliable think-tank is "Performance Simulations.com", Pond's trusted source?

Well, all I can say is that there is a guy with a computer and an interest in cars and video games living and located in St. Paul Mn. named Todd Wasson who agrees with Pond. He sells a piece of software and the quote from Pond is part of his puffery to get one to buy the software. He has sold 10 copies ($39.95 in e-format). Pond probably could be number 11. Performance Simulations.com is nothing more than that.

Live and learn, Pond.

-------------------------------------------------

For my part, I'd rather believe Boeing Aircraft which has a slightly bigger stake in calculating tire contact patch area:

Quote:
The tire contact area for any tire is calculated by dividing the single wheel load by the tire inflation pressure. If the load is expressed in pounds, and the tire pressure in pounds per square inch, then the area is in inches squared.
http://www.boeing.com/commercial/air...ontactarea.pdf
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Unread 03-11-2013, 08:46 AM   #35
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It's only logical. Try this thought experiment: Take a load range G truck tire (forgot how many plies) and while keeping the outside dimensions the same, keep adding more plies and rubber to it until the space for air is only a thin channel surrounded by rubber and steel, then disappears altogether.

At EXACTLY which point does the tire stop obeying the simple theoretical formula of weight, tire pressure and contact patch area?
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Unread 03-11-2013, 08:56 AM   #36
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Quote:
Originally Posted by MPond View Post
While thatís an interesting argument, itís incorrect. Your theory treats the tire like a balloon, and ignores the fact that tires are rigid and have a structure of their own. While the load on the tire and the inflation pressure do play opposing roles in how large the contact patch is, neither of those properties is linearly proportional to the size of the contact patch, or to each other. A 10% increase in load or a 10% decrease in tire pressure does not equate to a 10% increase in the contact patch. And comparable changes will not offset each other. While the load and PSI can be changed at will, the contact patch will always be limited by the tire geometry.
This^
...

In fact, it sounds familiar, albeit worded much better than I felt like typing out on my phone.

and this:
Quote:
See moronic computation above. I really like that "commutitive property" reference. I almost couldn't type I was laughing so hard.
, besides the autocorrect butchered typo, is clearly over your head. Guess they don't teach that in Ohio. A*B*C=A*C*B.

And I'm flattered you think I'm stalking you, but I still want you to go take that stroll in over the rhine.
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Unread 03-11-2013, 09:16 AM   #37
wilson1010
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Originally Posted by wolfcreek View Post
It's only logical. Try this thought experiment: Take a load range G truck tire (forgot how many plies) and while keeping the outside dimensions the same, keep adding more plies and rubber to it until the space for air is only a thin channel surrounded by rubber and steel, then disappears altogether.

At EXACTLY which point does the tire stop obeying the simple theoretical formula of weight, tire pressure and contact patch area?
I guess you have never seen a flat tire on a semi. How does this sidewall stack up in your fantasy?

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Unread 03-11-2013, 09:38 AM   #38
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I'm so tired of this moron...

Here's a great way for anyone here to see for themselves that Wilson is an idiot, spewing his "theoretical physics". Welcome to the world of applied physics.

This is my favorite way of checking contact patch. Yeah, it's not perfect, but it's quick and accurate. Get a piece of cardboard, jack the vehicle up, and put it under the wheel. Set it down (slowly, no squish factor needed here), and let it sit for a minute. The tread will compress the cardboard where it makes contact. Since the cardboard is one 1/8" thick, there's not much deformation, but there's enough to accurately see what your contact area is. You don't have to take my word for it, and we all know that 10 hours later Wilson will come back with some BS "theoretical" explanation for why it's wrong based on something he finally found on Wikipedia, or tell me I cheated and changed the tire pressure, or whatever else nonsense he can come up with to support his obviously incorrect stance he has dug himself so deep into there is no graceful way out of.

So don't take my word for it, feel free to try it yourself. Seriously, it only takes about 20 minutes. Here's what I did yesterday. 3 tires: a 125/90-16 (factory XJ spare, don't know how wide the wheel is), a 31-10.50-15 Duratrac on a 15x8, and a 33-12.50-15 KM2 on a 15x8, all set at 38 PSI, all on a 4 door XJ.












And here's the big one:






And your summary, and for the math-challenged Wilson, the area already calculated for you. (some slight rounding, but you can see the tape measure in the pictures before this)
The 33x12.50 measured about 6.5"x8.75", or about 56.9 in^2
The 31x10.50 measured about 6.25"x7.75", or about 48.4 in^2
And the spare 125/90 measured about 6.25"x3.5", or about 21.9in^2
How can this be? Same weight vehicle, same air pressure in the tires? It's because tires are not balloons, they are rigid, and have physical constraints, which does include the rim width btw.


Now, what Wilson is really talking about is contact pressure. A 4500lb object with 100in^2 of contact area will exert a pressure of 45 psi on the ground. That doesn't mean there's 45 psi in the tires (it doesn't mean there isn't 45 psi in them either, it's irrelevant).
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Unread 03-11-2013, 09:40 AM   #39
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[QUOTE=wilson1010;15114639]I guess you have never seen a flat tire on a semi. How does this sidewall stack up in your fantasy?

It's irrelevant to what I wrote. Sorry it went over your head.

I'll elaborate: The claim is that a standard tire obeys the mathematical relationship exactly. I'm going to assume that noone would assert that a solid tire obeys the relationship.
When transitioning from a real world tire to a solid tire there would then have to be a point where the mathematical relationship ceases to hold.
There is no logical basis for identifying such a point, as in "22 plies is ok, but when you get to 23, then it no longer holds".
Ergo, the only logical conclusion is that the relationship never held in the first place; it was only an approximation that really only holds for a theoretical tire of infinite pliability.
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Unread 03-11-2013, 09:43 AM   #40
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Wolfcreek, your problem is you proposed a though experiment. I'm sure you can see my point here.
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Unread 03-11-2013, 09:46 AM   #41
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Hahahaha! That is the funniest stuff I have ever seen. A moron trying to disprove the laws of physics with a tape measure and some cardbpoard. I guess that is what they taught at the "Number 1 College in the South" Not just the number 1 college in the south, the Number 1 College in the Whole South including Texas (which most literate people think is in the West, not the south.

:r ofl:

Quote:
Originally Posted by XJNKY View Post
Wolfcreek, your problem is you proposed a though experiment. I'm sure you can see my point here.
Now, what exactly is a though experiment? Help me with that one.

And:

Quote:
Now, what Wilson is really talking about is contact pressure. A 4500lb object with 100in^2 of contact area will exert a pressure of 45 psi on the ground. That doesn't mean there's 45 psi in the tires (it doesn't mean there isn't 45 psi in them either, it's irrelevant).
Of course it does, you moron. How could there be 45psi on the ground and not in the tire? You really have no understanding of pneumatics, do you? You seriously need to open up a textbook and read this for yourselves. 45psi on the ground but not in the tire you're nutz. You need to watch the Tim Allen movie Big Trouble. You're Eddie Ledbetter.
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Unread 03-11-2013, 09:58 AM   #42
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Ok, here's one for you. It isn't pneumatics, but it is still pressure distribution, although transmitted through a less-compressible medium. A gas piston, like in a pneumatic system, or a gun, has a surface area of 1 square inch. The chamber has a pressure of 2 PSI. At the other end of that piston, it tapers down to a geometry that has a surface area of 0.5 square inches. How much pressure is is exerted at the other end of the piston?

By your logic, 2PSI.
By people who understand physics, 4PSI.

You.have.no.idea.what.you're.talking.about.
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Unread 03-11-2013, 10:15 AM   #43
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See guys, this is a typical thread that has been hijacked by Wilson. He will argue for days, until he gets bored.

And each time someone presents a rational, logical argument that doesn't agree with his view of the world he will simply ignore it and make some other argumentative statement.

Usually this goes on long enough that he eventually contradicts himself, and then he runs away and hides until there's a new thread for him to hijack. I've been through this many times with him.

Let's get back to XJNKY's original topic: which tires would be better for his truck, used in a world of applied sciene (you know, where Wilson doesn't live)...
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Unread 03-11-2013, 10:51 AM   #44
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Just for the record; "For the past decade, Berea College has been consistently ranked by U.S. News & World Report as the number one comprehensive college in the South" It was #1 when I graduated in '08. That's from Wilson's favorite textbook, Wikipedia.

Also... he may have me on the Texas thing. Some rankings group them with the traditional "South" and some do not. Not really sure which way US News goes.

And I think I made up my mind on the tires about 2 pages ago. Since the sidewalls will pretty much be the same one way or another, and the skinnies are $30 cheaper per tire, and will hopefully let me squeeze some marginal gain in gas mileage out of that thing, I think I'll go with them. If it was getting enough pavement contact on the factory 245's for them to give it those tow ratings, I guess 255's will still be good enough. If it sinks in the mud because of the SMALLER CONTACT AREA (and subsequent higher PSI of tire contact), I'll just air them down, and refill them when I'm back on pavement. Plus, KM2's are probably going to get me out of things the FC2's wouldn't, just on tread design alone. If I ever do sink it, I'll make sure and take pictures, and bring them right back to this thread .

And as for Wilson... I grew up in the southern tip of what is considered Northern KY, which... to everyone who doesn't live there, is pretty much the same thing as Cincinnati. I've spent time in Cincy, and I hate that place. I can promise you, Wilson is not the only one. That is a geographic region full of some of the most obnoxious, clueless people I've met anywhere I've been. I've never been to NYC, but that may be the only place in the US where people might actually be worse than Cincinnati.

Quote:
Let's get back to XJNKY's original topic: which tires would be better for his truck, used in a world of applied science (you know, where Wilson doesn't live)...
And thank you for trying to help me bring this thread back on track. I still welcome any input from anybody with experience about the tire size/towing issue.
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Unread 03-11-2013, 10:56 AM   #45
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I would look to the owner’s manual and follow their guidance. Call me old fashion but that is what I would do. If more than one size was recommended I would choose which ever tire suited all my needs best.
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