How stiff are F1 tyres?

[Ciro Pabón]

Maybe this has been covered before, perhaps on another thread or in another lifetime, what do I know with Alzheimer?

Maybe the truth lies with God himself, you know, the big guy that makes me fall flat on my hard earned washboard-belly whenever one of my delightful but mischevious mistresses thinks it's funny to pull the plug on my inflatable mattress?

Life itself is such a mystery, why has Dolph Lundgren not yet been awarded with an Oscar, the hour is late for that?

The plot thickens.

Excuse me, I cannot respond right now while you roll around in bed with your lovers, I hear my kids laughing, must be something funny they read. I have to keep them from doing that, will be back.

Talking about thickening plots, I forgot to say that the rim is supported by the cable that goes around the circumference, which as I already said, it is connected to the suspenders. Something like this:

How a pneumatic tyre keeps your car from falling to the ground: the tread plays the part of a suspension cable in a suspension bridge, kept in place by pressure. The walls work like suspenders (the vertical cables in a bridge). The inner tyre cable (I don't know its name in english) works like the girders or beams in a bridge.


Ain't images wonderful?

[Tim.Wright]

Ciro, I have to respectfully challenge your view (not yet willing to disagree after half a bottle of wine )

I think the bottom does actually contribute to the supporting force. Obviously not in compresison, but by its reduction in tension. So I think its not correct to assume all of the vertical supporting force is coming only from the top half of the tyre.

Another force worth considering is the bead force which is acting to squash the rim under static conditions. Maybe JT can eleborate as to weather this is comparable in magnitude to dynamic vertical loads.

I actually find round things quite annoying to analyse. Though if they were so simple, I probably wouldnt have a job

Tim

[Ciro Pabón]

Bead, that's the name in english! Thanks, Tim. Yeah, sure, give me more examples of cables supporting something under compression. I'd love to hear that.

I'm no tyre expert, so you might be right, but in my experience, I'm never wrong (ha, ha, how funny I am!). Care to draw how it works so I can understand it? How is exactly the force transmitted to the rim from the tensioned walls at the bottom? Perhaps there is some residual force there (after all, even bicycle spokes at the bottom of a bicycle wheel could make some kind of force, they are not compressible without SOME effort, but...).

Please, you do not have to respect me (although, thanks from the bottom of my heart). After all, I was mod for (what seemed) ages, I find strange the day people in this forum respect my point of view. I love impertinence. So, go for it! Do not care for my sensible ego, I don't have one. Thinking about it, I'll go for half a bottle of wine I have downstairs to equalize things. In half an hour I will be saying that "I love you, man! You are the best friend in the whole world!".

Besides, I think we have contributed A LOT for the people in the forum to understand how their cars "float over the road". And, no, it's not magic (yet!).

[ringo]

Well, everybody is wrong. xpensive ALMOST got it right but then he blew it (ha, ha! How funny I am!) by saying that is the pressure what keeps the vehicle above ground. Wrong, X.

I know this will come as hard to understand, but the pressure in the tyre is not what supports your car. Please, read this twice, in bold and large, as I have a tendency to write like this the things that I think are important to understand:

The pressure of the air inside the tyre is NOT what supports the vehicle.

The vehicle HANGS from the tyre through the cords that form the tyre. The air pressure simply keeps the TOP of the tyre from collapsing.

Now, the picture I always provide (besides the one thousand words it is worth).

Tension is inversely proportional to radius of curvature!


So, it is exactly like a suspension bridge. The top surface of the wheel is the equivalent of the suspenders, the walls are like the suspension cables. The top of the wheel is stiffened by the air pressure inside. So, the walls in the upper circumference of the wheel is what keeps the vehicle from falling down.

How could it be otherwise?


No, it isn't


As xpensive pointed out, pneumatic tyre works like a spoked wheel in a bicycle. The wheel is not supported by the spokes in the lower part of the tyre, it is hanging from the spokes in the upper part of the circumference.

Now, don't give me theories about bulging sides keeping the wall from collapsing, X. It's the top, not the bottom.

How is the load transmited to the rim? Simple: the walls at the bottom flex and the TOP of the tyre becomes more flat. This raises tension on the cords at the TOP and it diminishes tension at the BOTTOM cords.

Any civil engineering student can explain to you that in any structure that works in tension under pressure (that is, inflated), the tension of the wall is inversely proportional to radius of curvature.

And having said that, I go out of this thread, as I have no idea of the stiffness of an F1 tyre. Let's pray to the god of atheist for an actual tyre engineer to come into this thread.

Hrumppph... tension in the wall increased by bulges... I cannot believe the things one has to hear these days! Were you asleep in class? Was your teacher asleep in class?

I read tyre threads to learn but hardly post, because tyre construction and dynamics are too peculiar. However i would also say that the tyre is still supported by the air pressure. Your post doesn't counter that point, it only specifies which side, the top side, is doing the supporting.
The air is what's proving that tension in the cables via the hoop stress.
The bottom side wall cables may not be supporting the vehicle, but the same pressure that provides the tension in the top is still resisted by the lower sidewalls anyway.

I happily take tyres for granted, too much damn things going on in them. Gimme the data sheet and that's all. I'm like Alonso being chased by Hamilton, i'm on a need to know basis.

[xpensive]

...
Talking about thickening plots, I forgot to say that the rim is supported by the cable that goes around the circumference, which as I already said, it is connected to the suspenders.
...

Suspenders eh? Reminds me of an obese old friend of mine that always underlined that his rondeur, or rather apalling fatness if you ask me, was due to his aim to keep his skin stretched and wrinkle-free. Well, I guess that worked for him.

Wonder what keeps tires, yes tyres with their suspenders, free from such wrinkles?

[Ciro Pabón]

...However i would also say that the tyre is still supported by the air pressure. Your post doesn't counter that point, it only specifies which side, the top side, is doing the supporting...

That's what I call to be "hanging from a tread" (three jokes in two pages! all relevant! and with wordplay! I'm in a row! More exclamation marks! Nice recourse! Another one!).

Look, you could use a steel tread, stick regular walls to it and use the bead (thanks, Tim) to hang the tyre from those walls.

Becoming a serious person again, lemme asure you, dear ringo, that there is a LOT of hard data that proves that inner pressure is NOT related to contact patch pressure.

So, ringo, an ideal tyre would have a sidewall with not flexural stiffness at all and a very high tension modulus, like fabric or steel cables. However, steel cables do not hold air, thus you use rubber to keep the air inside. Rubber produces friction every time it flexes. This flexing produces rolling resistance, which is undesirable. Thus, you use as little rubber as you can. A bicycle tyre is a good example of how you achieve that.

X, your jokes about fat guys with tyres on their bellies slip on me, like a Pirelli at Loewe. I'm a 6 foot, 78 kg guy, divorced, I haven't even girlfriends and live in Cali, sin city.

[DaveW]

Ciro, re your suspension bridge analogy. Sorry to be pedantic, but I think that it is the towers, rather than the suspension cables or the "suspenders" that actually keep the deck out of the water (although all contribute, of course).

Another thought. Tyre vertical stiffness does vary with pressure, usually increasing with increasing pressure, but not always - some will increase stiffness with decreasing pressure.

[KSP]

Ciro, try to cut off the top half of the tyre and throw it into the garbage, seal the holes in the bottom half and inflate it. Do you think that rim didn't rise above the ground?

[Ciro Pabón]

Ciro, re your suspension bridge analogy. Sorry to be pedantic, but I think that it is the towers, rather than the suspension cables or the "suspenders" that actually keep the deck out of the water (although all contribute, of course).

Another thought. Tyre vertical stiffness does vary with pressure, usually increasing with increasing pressure, but not always - some will increase stiffness with decreasing pressure.

Well, Dave, you support part of the weight on the towers, but you don't have to. Besides, theh stiffness of the girder is very low, it cannot take high cantilevered loads. Most of the load goes through the suspenders.

Look, Dave, no towers!


Actually, at the towers of most suspension bridges and almost always at the abutments you attach the girder to the tower with links that allow the girder to move freely. The girder would break if attached rigidly to the tower, because the cables cede a LOT.

[Tim.Wright]

Hey Ciro,

Here is what some vino rosso from Maranello has inspired me to do. This is my understanding on how the bottom half of the tyre contributes to the vertical loads passed to the wheel.



Its very similar to the mechanics of a bolted joint in terms of there being two preloaded "springs" acting against each other. In both cases (bolted joint or a tyre) the application of an external load is balanced by an increase in force from one element, and a decrease from the other element. Do a search for "bolted joint diagram" to find a few good pages explaining it.

Tim

[marekk]

Well, everybody is wrong. xpensive ALMOST got it right but then he blew it (ha, ha! How funny I am!) by saying that is the pressure what keeps the vehicle above ground. Wrong, X.

I know this will come as hard to understand, but the pressure in the tyre is not what supports your car. Please, read this twice, in bold and large, as I have a tendency to write like this the things that I think are important to understand:

The pressure of the air inside the tyre is NOT what supports the vehicle.

The vehicle HANGS from the tyre through the cords that form the tyre. The air pressure simply keeps the TOP of the tyre from collapsing.

Now, the picture I always provide (besides the one thousand words it is worth).

Tension is inversely proportional to radius of curvature!


So, it is exactly like a suspension bridge. The top surface of the wheel is the equivalent of the suspenders, the walls are like the suspension cables. The top of the wheel is stiffened by the air pressure inside. So, the walls in the upper circumference of the wheel is what keeps the vehicle from falling down.

How could it be otherwise?


No, it isn't


As xpensive pointed out, pneumatic tyre works like a spoked wheel in a bicycle. The wheel is not supported by the spokes in the lower part of the tyre, it is hanging from the spokes in the upper part of the circumference.

Now, don't give me theories about bulging sides keeping the wall from collapsing, X. It's the top, not the bottom.

How is the load transmited to the rim? Simple: the walls at the bottom flex and the TOP of the tyre becomes more flat. This raises tension on the cords at the TOP and it diminishes tension at the BOTTOM cords.

Any civil engineering student can explain to you that in any structure that works in tension under pressure (that is, inflated), the tension of the wall is inversely proportional to radius of curvature.

And having said that, I go out of this thread, as I have no idea of the stiffness of an F1 tyre. Let's pray to the god of atheist for an actual tyre engineer to come into this thread.

Hrumppph... tension in the wall increased by bulges... I cannot believe the things one has to hear these days! Were you asleep in class? Was your teacher asleep in class?

A spoked wheel in a bicycle isn't hanging from the spokes in the upper part of the circumferrence. Except for a few spokes directly above roads surface, all others are simply preventing deformation of the wheel, efectively converting the top-down load to radial tension on the spokes.
In the very same way a pneumatic tire doesn't hang from it's top. What realy keeps our cars above ground is nett change in air pressure. After applying a load to the tire, you change it's shape and volume - that means you change air's pressure. This change in pressure acts as a force on whole surface of the tire and rim, and, lacking a possibilty to expand it, creating tension forces in all parts of this system.
It's maybe a litle bit dificult to imagine, but all of the car's weight is "hanging" from the whole tire to the rim

[DaveW]

Ouch... An elegant reposte, Ciro, & a rather better analogy, perhaps. But I don't think either is an accurate illustration of the way tyres react vertical loads. Apologies...

[Ciro Pabón]

Please, Dave, I repeat, I don't care if people points to mistakes I make.

Thanks, KSP. Good question. It is good, of course, because it helps to clarify things, not because the explanation is wrong. Remember: I'm never wrong (and "when I'm wrong, I'm enchanting", as the mexican song goes. That is another joke, of course I'm wrong sometimes, but I accept the fact as soon as I can. I was married, for example).

The problem with your half tyre is that IT IS NOT ENOUGH TO "seal the top and bottom". If you do that, then the bead will pop out. The tyre will "fall" trough the bead.

So, for your half a tyre to work you would have to seal the rim inner part, like this:

Notice you would have to attach the red "seal" to the bead at the yellow points. This is where the force would be transmitted to the bead and then to the rim. The bead would have to go around the top of the tyre anyway, to be able to "hang" from the rim. The red seal will work in tension, of course, like any rubber membrane does


Notice what you have done: you are "inverting" the suspension cable. Now, the tyre is not supported by the tread on the top part of the tyre: it is supported by the "inner tread" on contact with the inner part of the rim and this force is transmitted then to the bead directly. You have taken the walls out of the equation and suspended the bead directly from this new "hidden" tread.

Tim, thanks, nice picture. Maranello is inspiring, I agree on that. Sure, probably there is some residual force on the bottom half of the wheel, but even in an wheel like the one you are picturing, the compression doesn't work very hard. The diagram on the left shows you the actual tensions caused by inflation, not the reactions to the weight of the car.

I repeat, the bottom part of the wheel works like the spokes on a bicycle tyre, they provide you some resistance, but they aren't able to stand the force that actually goes into the steel at the top, that probably is around the number mentioned before (several thousand pounds per square inch).

I do not have much else to contribute and a lot of work to do. I'll be back tomorrow, to see if somebody has given a number to stiffness (wich, in the case of a quarter car model, for road design is around 300 N/mm).

[ringo]

...However i would also say that the tyre is still supported by the air pressure. Your post doesn't counter that point, it only specifies which side, the top side, is doing the supporting...

That's what I call to be "hanging from a tread" (three jokes in two pages! all relevant! and with wordplay! I'm in a row! More exclamation marks! Nice recourse! Another one!).

Look, you could use a steel tread, stick regular walls to it and use the bead (thanks, Tim) to hang the tyre from those walls.

Becoming a serious person again, lemme asure you, dear ringo, that there is a LOT of hard data that proves that inner pressure is NOT related to contact patch pressure.

So, ringo, an ideal tyre would have a sidewall with not flexural stiffness at all and a very high tension modulus, like fabric or steel cables. However, steel cables do not hold air, thus you use rubber to keep the air inside. Rubber produces friction every time it flexes. This flexing produces rolling resistance, which is undesirable. Thus, you use as little rubber as you can. A bicycle tyre is a good example of how you achieve that.

X, your jokes about fat guys with tyres on their bellies slip on me, like a Pirelli at Loewe. I'm a 6 foot, 78 kg guy, divorced, I haven't even girlfriends and live in Cali, sin city.

Oh so your not a mod any more eh?

Saying the tyre isn't supported by the air pressure or at least party supported by it is not accurate.
The tension in the cables is provided by the air pushing against it's container walls which is the rubber lining as you put it.

To be precise the rubber has a component of stiffness which is partly supporting the car, but the air pressure makes a contribution.

Just as you can apply a civil engineering principle to a tyre, a pressure vessel application can be made to it as well.

For an unloaded tyre, the air pressure provides the tension in the cables, assuming the cables aren't prestressed in the wall of the tyre.

You should draw your free body diagram. What's supporting the tension cables?
The rubber wall? What if the rubber wall is beach balloon thin?

an ideal tyre would have a sidewall with not flexural stiffness at all and a very high tension modulus

explain this, and how it relates to supporting a vertical load.

[Jersey Tom]

Ciro's pretty much got it, at least for F1 tires.

As for whoever wanted lateral, longitudinal, and torsion stiffness of said tires - not gonna happen.