Well i'm a little confussed as to the amount of air to run in my tires. Lately in the forums posted people are running much higher lbs. than what the recomended lbs. should be, as i can understand the advantages of a couple a couple of lbs. but 15 to 20 i don't understand. CONFUSED IN CALGARY CA.

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99 honda 450es locked,27" xts,

 

Same here, some guy said he was running 42 lbs!!!!!!!! i was like what the hell are you thinking? but if they want to go through tires every month i guess let them.

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RangerSX 1987 Honda 250X(completely stock)

 

It will not hurt the tires by putting alot of air in them, it gives a taller hieght and alot rougher ride, and less traction or rubber on the ground. More air also gives better flotation in deep water. I have 60 psi in my rear 25X12-11 vamps to get them seated on my stock rims. I now run 10 psi in the rear and 15psi in the front. However I am going riding today in some really muddy conditions and I think I'm gonna drop them down to about 5-6psi all around.

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Matt Sibley

1999 Honda 300 4x4 Vampires, Lift Kit, 2500lb WARN winch

 

I can understand the difference of more air in frount to ease on the steering but i run a locker (doin't get me started on that) i'm not sure i would srew up something on my locker having two diferent size tires from having less air in one than the other.

 

dirtyhowies, mis-matching front and rear tire diameters (by overinflation)stress the drivetrain to some degree whether you have a locker or not. The locker is of no consequence in this issue.

In 4WD, front and rear dirveshafts turn at the same speed; the left and right rear tires are already spooled, so they turn at the same speed; with your locker, your left and right front tires turn at the same speed. Ground-slip between different diameter front and rear tires stresses the drivetrain, locker or not, except in 2WD. In 2WD, no front-to-rear drivetrain binding occurs.

No one has mentioned an issue of concern; tire sidewalls sometimes list operating and maximum pressures, including bead-setting maximum. Exceeding these pressures might be hazardous to a tire's health, I should think.

Tree Farmer

 

The idea behind running lots of air pressure is for maximum flotation and ground clearance... But, honestly, I think anything beyond about 20 p.s.i. is just going to beg for tire ruptures and punctures. For the most part, the tire carcass will be stretched to its max by 15 p.s.i. at 20.. its not going to be any bigger, just may float easier. I run about 12 in the Magnum with 27" Blackwaters.. it keeps them seated good, floats pretty good, and YES the ride is rough.. but thats a trade off i'm willing to live with.

 

I'm confused at the notion that more air in a tire makes it float better. Bouyant force ("Floatation") is a function of the specific gravity of the fluid, and the submerged volume of the object. The weight of the vehicle makes it sink, and the volume of water it displaces makes it float, or feel lighter in the water. An example: notice how a heavy object is easier to move when underwater, or partially submerged.
So, the tire would have to stretch and become larger to increase a vehicles' bouyant force. I didn't think ATV tires would stretch a heck of a lot. And actually, when you increase the pressure of the air in the tire, you increase the air density. You're stuffing more air molecules in the tire, increasing the weight of the tire, reducing flotation. Probably negligible, though.

If you are talking about floatation over the mud, the best way to combat sinking into the mud is low ground pressure. This is vehicle plus rider weight, per square inch of tire contacting the ground. Reducing the tire pressure will squash it out, leaving more tire contacting the ground. This reduces the vehicle ground pressure, increasing your ability to kepp the vehicle on top of the real soupy, peat moss crap. I you watch automobile mud dragsters, you'll notice they have fatter tires to keep them from biting too deep in the mud, which reduces speed and momentum. Also like if you are going across real thin ice. If you stand up, you'll fall through. But if you lay flat on the ice (same body weight/increased contact area = results in lower ground pressure), you will stay on top if it.

 

More air pressure means more floatation theory:

Increasing tire pressure does increase flotation some extent, but not how you might think. For example if you have 5 lbs in one tire that will float 20 lbs. Then you increase it to 10 lbs, doubling the tire pressure, does NOT mean it will now float 40 lbs. The increase if even noticeable will be relatively small when dealing with the small numbers that we are with ATV tire pressure. It would probably not be worth the excessive roughness of ride, the chance of blowing out a tire or stretching the sidewalls thus increasing the chance of punture.

I do run alittle more than stock recommends to increase ground clearance, make it harder to unseat the tire beads and to ease steering. I usually run about 5 lbs front and back. Enough to keep the tire from really squatting when appling my weight.

We discussed this in my Physics class many years ago and don't ask me to try to explain it, I just remember it. There is some formula for it...

Please feel free to expand on....

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Gap Arrington Dickson TN Honda ForemanES "and Yeller at that!"

 

FLOTATION

Summary:

"Flotation," and "floating," involve two different concepts in the tire context.

Flotation means the ability of a tire to support a load on a surface; the lower the pounds-per-square inch, the greater the flotation. Flotation can be increased by releasing air from a tire if its footprint, its area in contact with its supporting suface, increases. "Airing down" increases flotation.

Floating means the ability of a liquid to support a weight. Since the weight supported equals the weight of the liquid displaced, increasing a tire's volume by adding air, making it fatter, increases its ability to float.

Discussion:

"What we have here, is a failure to communicate!" (from "Cool Hand Luke;" rent it at Blockbuster's).

English sometimes appears an imprecise language. "Flotation," for example, has multiple meanings; and meanings that may be significantly different from "floating."

Traction-wise, flotation generally means, the inverse of weight/surface area, as in pounds/square inch; I said inverse, so the lower the pounds per square inch, the greater the flotation. This classic definition has been used for military vehicles for a long, long time; a tank, for example, has better flotation, than a Jeep (because of the tank's extensive surface contact area from its tracks; a tank does not "float" better than a Jeep!). Thus, Moses is correct in this context. "Air down" the tires, allow air to escape, creating a bigger "footprint," the area of tire in contact with the ground, and you INCREASE flotation, as defined in this situation.

But his name is "Moses," not "Archimedes," whose argument Gap_Arrington pursues. Archimedes' consideration of flotation, or more appropriately, "floating," holds that the weight supported equals the weight of the liquid displaced by an object. Thus, as long as air is added to a tire, and the tire's volume expands to a degree greater than the weight of the liquid displaced exceeds the weight of the additional air, the tire (and attached vehicle) becomes more inclined to FLOAT. If we're talking about whether an air-tired vehicle floats or sinks in a liquid, in practical terms, Gap_Arrington is correct in his physical understanding: a fatter tire, filled with something lighter than the liquid supporting it, is more likely to float than a thinner tire.

However, we're talking about two exceedingly different concepts:

FLOTATION, meaning a tire's ability to bear weight on a surface; and

FLOATING, whether a tire (and perhpas its attached vehicle) floats or sinks in liquid.

Preserving harmony, let's say both Moses and Gap_Arrington are right!

Tree Farmer

P.S. The airlines don't help any! If you've flown commercially, you've doubtlessly heard and read, "In the event of an emergency landing over water (translation: crash/ditch), bottom seat cushions may be used for FLOTATION." (emphasis added). The airlines use the word, "flotation," in this spiel as a euphemism--"flotation" is less apt to conjure up its opposite meaning that the word, "float" (whose opposite is "sink"), in the mind of the terrified passengers! Think of it! Gentle, benign, and passive "flotation," much more comfortable that "floating," while desperately clinging to a silly seat cushion while sharks nibble at your lower extremeties!

T.F.

[This message has been edited by Tree Farmer (edited 01-18-2000).]