# How is a car with tubeless tires supported?

#1

What actually supports a car with tubeless tires?

My vote is the axle is supported by the sidewalls, hanging down from the top of the tire. It certainly isn’t the air pressure on the axle which is the same all the way around. I’m troubled that I can’t find anyone to agree with me!

#2

There must be a reason why you can’t find anyone who agrees with you. Recon what it is?

#3

“It certainly isn’t the air pressure”

Can’t imagine why no one agrees with you.

#4

Um, it’s the air pressure in the tire, which is the same all the way around, but is sufficient to support the axle, and the vehicle. Why do you have a problem with tubeless tires? They’ve been keeping wheels off the ground for YEARS. This is not something new, and really no different from tubes. The tubeless tire seals against the rim, or wheel, and holds pressure just like a tube would, only a tube is no longer necessary.

Do you have a vehicle that does NOT have tubeless tires?

#5

Maybe I should restate the question. How “exactly” is the weight of the car transfered from the axle to the ground? Magically by air pressure all around the axle if I understand these first replies correctly.

#6

Flagged.

#7

When a tire goes flat, the volume inside the the tire is less than an inflated tire. Air resists being compressed into a smaller volume. Moreso when it’s under pressure. Therefore, a tire with pressurized air inside will resist being compressed into a flat tire. Voila! magic air pressure supporting the weight of a car.

#8

You magically avoided answering the question. Of course an inflated tire resists being compressed. And inflating a tire will blow it up and lift up the car. But that pressure is transmitted equally to the axle on all sides. The air presses down as hard on the axle as up on it. What exactly does the air press against to lift the car? The center of the expanding tire lifts the car. The center of the tire is lifted by the sidewall of the tire. Therefore the car is suspended on the UPPER sidewall of the tire

#9

You’re magincally overthinking this.
Through a complex relationship between the tire, rim and air pressure, the tire transfers the forces of the air pressure through the bead of the tire into the rim and into the axle. Really, it’s that simple.

Not avoiding the question, just trying to provide a laymen’s answer to an otherwise very complex free body force diagram.
Just out of curiosity, are you an engineering student?

#10

What actually supports a car with tubeless tires?

It’s the payments and tithing to a reputable mechanic.

#11

Just so you don’t think you are alone:

I attended a tire seminar with my fellow tire engineers and the vast majority more or less agree with you. The air pressure stiffens the tire, but doesn’t support the load.

Many folks think the footprint pressure equals the inflation pressure - which should be the consequence if the pressure by itself is carrying the load. There is ample data to refute this.

#12

And I thought the government caused inflation. Politics is so much easier.

#13

A tire body by itself without compressed air in the tire will support some of the car’s weight but only a little like a hundred pounds or so. The car’s weight at that particular corner is imposed on the axle which in turn rests on the wheel which in turn is supported by the tire carcass which is made resistant to flattening at the bottom because of the tire body’s stiffness plus the air pressure inside the tire. The weight of the car will not “hang” from the top of the tire as the top of the tire is not fastened to anything. It might be possible to know the distribution of the car’s weight imposed on the tire with an FEA (finite element analysis) engineering computer program. Now, I have to ask, what will you do with this infomation when you get a satisfactory answer?

Tubeless tires do indeed have a tube. It is the airproof rubber lining the interior of the tire. It just happens to be fastened to the tire.

#14

The same as tube type tyres. The air.

I can’t be 100% certain but this one sounds like a troll.

#15

I’m not an engineering student, but my son was. Even his professor got this one wrong.

I think we more or less agree. However, almost everyone else thinks the air somehow directly supports the load. (See a few of the replies here) In reality, the air pushes up the top of the tire which then lifts the entire carcass, including the axle that is attached by the bead.

To continue the analysis, the top is the only place where the internal air pressure forces against the tire are not balanced on the other side of the tire. On its opposite (bottom) side, the air pressure is equal and opposite to the force of the ground underneath. So effectively, this ground force is indirectly transmitted by the air pressure to the top of the tire, lifting it and the axle along with it.

#16

Thanks, see my comment to McBean above. I chose tubeless because considering a tube simply confuses the analysis.

As for what I will do with this info, nothing. I enjoy knowledge, puzzles and conundrums for their own sake,kind of like the car talk puzzler, and maybe sometime in the future it may connect with another interesting tidbit, like does the number of sidewall layers in a tire relate to total load or maximum air pressure?

#17

I think a full analysis will show that the whole circumference of the sidewall is supporting the wheel, which in turn is supports the axle. Suppose you have a flat tire, not damaged, just not inflated. All of the weight is resting on the wheel rim and the tread of the tire. Imagine you add a little bit of air pressure to it, this raises the wheel slightly, but if you were truly pulling the weight up by the top of the tire it would unseat the bead. The entire bead area of the tire is holding some part of the load. The air pressure stiffens the sidewalls and the bottom of the sidewall also supports some of the weight. The air pressure is not “magically” holding up the axle, it’s holding it up via the sidewalls all the way around.

#18

Um, perhaps it’s the tendency of the pressurized air captured in the tire to want to maintain equal pressure throughout its volume when the portion of the tire in contact with the road is pressing on that spot and trying to further pressurize tha already pressurized air?

So, how does a bicycle wheel hold up the the axle? It’s a suspension device! It hangs from the upper spokes!

So tell us, what did your son’s professor say?

#19

Visualize, if you will, all of the tire cut away except perhaps the bottom fourth of the tire. Then if you could, cap both open ends of the tire section and add air. The tire section will keep the car axle where it would be if the whole tire was there.

#20

Interesting point. Air being a fluid, it insists on conforming to the shape of its container and maintaining equal pressure on all surfaces. Changing the shape of the container does not change the physics, and containing the air compressed between the wheel’s bottom and the portion of the carcass in contact with the pavement in a different shape container does not change its ability to hold up the car, as long as the air is contained. That would make the compressed air the thing holding the car up rather than the sidewall. The sidewall’s contribution is to contain the compressed air.

I agree.