ok look at it this way. Your car is riding on a cushion of air. The air is held in place by the rubber of the tire. It’s like a balloon.
The air pressure is equal on all sides of the tire, but on the bottom, the ground is pressing against the tire, which presses against the air, which presses against the wheel.
The sidewall of the tire supports the weight of the vehicle at the point where the tire is in contact to the ground.
If you don’t believe me, just let the air out of a tire, and what part of the tire deforms as the air is let out?
Tester
What is the problem with the idea of distributed forces through captured air? The force of gravity is distributed, through the captured air, to all of the sidewalls.
The tire holds up the car.
The air pressure keeps the tire in a rigid position so that it is capable of holding up the car.
It works the same as tires with tubes.
Gravity = A downward force.
Pressure = A force that goes in all directions.
Tester
I disagree. Changing the shape of the air container changes the problem.
Consider: It is easy to see that if the air container is situated bewteen the rim and the ground, then the upward pressure is balanced against the downward pressure - just like a bottle jack.
But when you look at the tire in its entirety, there is also a force pushing the rim downwards (from above) - and that force is equal to the force pushing the rim upwards. No matter how you slice the tire, the pressure creates a force in the tire that transfers the load being carried upwards.
The tire sidewalls supports the weight of the car. The air pressure inside the tire keeps the sidewalls rigid enough to actually support the weight. remove the air pressure and the sidewalls collapse under the weight of the car. So to answer your question, the tires support the weight with the air pressure supporting the tires.
Yup, the compressed air is pushing the rim toward the center with the same force it’s pushing the carcass outward, in essence pushing the rim away from the casing of the tire and keeping everything supported. The tire simply controls the shape of the cavity in which the air is compressed as well as how the cavity distorts under varying conditions…like a bump or an added member of weightwatchers. Sectioning the tire doesn’t change this. It only changes the way the cavity would distort.
The sidewall doesn’t support the weight. The compressed air pushing in all directions does. The sidewall controls (along with teh rest of the carcass) the cavity characteristics.
“…like does the number of sidewall layers in a tire relate to total load or maximum air pressure?..”
No! The answer is way more complicated than we have space for here. If you are interested in the lengthy discussion, see me at www.allexperts.com. I’m the only tire engineer, there.
Agreed. But that does not lead to a deduction any different than that I’ve stated.
Compressed fluids work to hold up a load the same in a tire as they do in the hydraulic ram of an excavater. The physics is the same. The only difference is that the tire allows the containment to change shape to absorb impact.
You know, I think the way to envision this is to imagine not a tubeless tire, but instead envision a tire tube. Make it a tube for a 20 inch tire and put it around a 15 inch wheel, or even just the axle. If you put a deflated tire tube around the wheel and then inflated it, eventually you would have the wheel resting on the bottom inner diameter of the tube, and probably not even touching the top inner diameter. Clearly, with a tubeless system the wheel forms part of the “tube,” but it is indeed the air pressure supporting that wheel.
Yup. Pressurized air will support the wheel as long as it’s contained in any form of container that does not allow it to expand and the container is placed under the wheel. It does not need to be a tire. As a matter of fact, if you doubt this, visit http://eeresq.com/_wsn/page5.html. They sell emergency airlift bags and system. They can lift the whole vehicle!
Compressed air can lift the wheel without the tire, but the tire cannot lift the wheel without the compressed air. A tire does no lifting.
Hey OP, what did your son’s professor say? I’m really curious.
2 thoughts:
If a tire cannot lift the wheel without compressed air, how do runflat tires work? The only difference is the stiffness of the sidewalls!!
Remember what we are lifting - the car - is not on the top of the bag - it is in the middle. Imagine a fully extended bottle jack where there is an extra cylinder in the middle. The pressure above the cylinder is the same as the pressure below the cylinder. That cylinder will fall unless there is something holding it up - in this case the tire.
Runflats have a doughnut inside the tire.
Or, in one type, reinforced sidewalls that can provide some support even without air. In that case, the sidewalls can support their corner of the vehicle without air under limited use. Remember that the post doesn’t ask whether a tire can be created that’s capable of supporting a car, but rather what holds up a car in a normal tire. Heck, a solid rubber tire could be made that could easily support a vehicle, but that wasn’t the question.
It’s the pressure INSIDE the bottle jack that lifts the vehicle, not the jack itself. Without the fluid pressure inside the jack is useless.
Check the website. Those airbags are designed to lift loads quickly and safely in emergencies; beams, cars, trucks, whatever. The bag goes under the load. European race teams also use a flat bag that slides under a low-clearance car and blows up to lift the vehicle in the pits. I myself was thinking of getting one to use with my compressor to lift he car to put the jack stands under.
Same way as a car with tubes, or a bicycle for that matter. I’d recommend a physics course or two and will go a long way in explaining some of the wonders of the world.
The car is supported by the same thing that supports YOU when you lay down on an air mattress.
It’s the air. Naturally.
Nothing too great. Didn’t like my analysis but didn’t present his own.
In response to several posts.
Thanks to those who provided reasoned feedback. The chatter has helped me formulate my ideas in a more comprehensible manner. This is a far more complex and interesting analysis than it appears on the surface.
I suggested a tubeless tire to prevent false analogies such as made by Ranck. A properly pressurized tube will completly fill the inside of the tire carcass, pressing itself equally against all walls and axle with the same pressure. There is ALWAYS a downward air pressure on the top of the axle that compensates for the upward pressure. All the tube does is provide a tight seal for the air to prevent its escape from the tire. So why not remove the tube! The analysis will be the same.
Any soft inflated object can support weight placed on its top. Probably something as simple as a basketball inflated hard enough would lift a car. But that is a somewhat different problem. Such an inflated object under a weight will deform so that the surface area against the object being supported will flatten until the surface area times the pressure balances the weight. Picture a balloon pressed down, or even between your hands; internal pressure may change slightly, but principally it flattens against your hands to resist the pressure. (The bottom of a tire deforms similarly)
So lets imagine basketballs instead of tires. Imagine two basketballs supporting an axle “glued” between them. (If it helps, imagine a lot less weight than a car). At first they are not inflated. As they are inflated, the top of the balls will expand first because nothing is resisting their expansion. Then the bottoms will expand, lifting the axle. But how? The air is not directly lifting the axle, the ball carcass is. But how is the ball carcass lifting it? The wrinkled up bottom has no strength to lift it. There is no air pressure force pushing up any portion of the basketball carcass below the axle. The only place the air pressure force acts in an upward direction on the basketball is above the axle. So therefore the axle is being lifted by the top of the basketball carcass.
Now lets replace the basketball with a tire. There is too much load to reasonably “glue” the axle on or otherwise attach it to only one side, so it runs through the tire, stabilizing it. The air pressure is equal on all sides of the axle so it has no other effect. How the sidewall deforms below the axle also has no effect. Although there are some outward bends in the flat tire being pushed up by air, for evry such bend, there is a compensating sideways bend back that is pushed down.
Thanks for the informative reply. I’ve had years of physics and engineering courses. I’m a degreed engineer with 18 patents. And you?