How stiff are F1 tyres?

[Ciro Pabón]

Again, ringo, you're right in the sense that the pressure is what keeps the top from collapsing. If the tyre had very thin rubber walls, but you keep the inner steel structure, the walls would balloon, but the tyre would hold the load through the steel (assuming the rubber walls are allowed to expand as much as needed and they do not blow out AND the rubber is attached to the steel cables at the top, working IN TENSION).

If I am wrong, explain to me why steel cables are needed at all and how they work in compression.

Let me assure you rubber doesn't work in compression at all (well, maybe it will give you a few grams). Unless you explain that, all the explanations that try to involve the tyre walls at the bottom supporting the weight are flawed.

I can also tell you that old Pacejka agrees with this explanation. I try to never be final on anything unless I read about the subject. When I'm not sure, I start all phrases with "I think" or "Warning, original research!". However, I hate to give arguments from authority, so, tell me if now you find this convincing.

I won't repeat myself, so, I think this is all I can contribute. If someone else has a reasonable explanation, I'll read it, rest assured.

Thanks, Tom, I knew one is never alone, and, even if you are, "there are those wonderful books whose authors send them to the world, like ships to the sea"...

[marekk]

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.

More load = more contact patch area = less inner volume = more inner pressure.
Simple as that.

[Ciro Pabón]

Sigh. Last post, I swear (every time I hit "Send" there is somebody contradicting me!).

Of course the patch increases. I quote here and I WON'T EXPLAIN. Those who had ears, listen:

"Three factors are involved.

Tyre carcase stiffness from the rubber and reinforcement fabric.

Air pressure.

Dynamic effects.

The air pressure is full adjustable, but the structure is fixed.

When the tyre is dead flat, structure controls 100% of the contact area. The higher the air pressure, the more it over rides the structure. Dynamic effect vary with speed."

As for torsional stiffness, JTom, perhaps you have at hand Pacejka "Tire and vehicle dynamics" AND a scanner (I'm not even close to my bed, much less an scanner). Chapter 9.4.2 is probably what is needed here, I know it shows modes at 30 to 100 hz.

Man, this is worse than explaining friction not being proportional to load! (of course, someone will point to me that friction increases with load AND that I just mentioned the word rubber together with carcase stiffness, sigh). Have you seen Scott Pilgrim vs the world? (btw, very funny movie, I recommend it...).

Hopefully, all those years of consulting for private firms and having to argue week in and week out with two dozen inept government officials that do not read AT ALL, at supervising meetings, have given some fruit.

JTom, help me! They are harder to convince than my mom (and she's a 75 years old spaniard!).

[Jersey Tom]

Meh, I gave up. Don't have time these days either. Started work at the race team this week. Busy busy.

[ringo]

Again, ringo, you're right in the sense that the pressure is what keeps the top from collapsing. If the tyre had very thin rubber walls, but you keep the inner steel structure, the walls would balloon, but the tyre would hold the load through the steel (assuming the rubber walls are allowed to expand as much as needed and they do not blow out AND the rubber is attached to the steel cables at the top, working IN TENSION).

That's what i was saying. The air pressure is partly responsible for the tension.

If I am wrong, explain to me why steel cables are needed at all and how they work in compression.

I never said you were wrong, i said you weren't 100% correct; which is just from my simple attempt at understanding what is happening.

Let me assure you rubber doesn't work in compression at all (well, maybe it will give you a few grams). Unless you explain that, all the explanations that try to involve the tyre walls at the bottom supporting the weight are flawed.

I wasn't arguing that. Even if the side lower wall doesn't support the weight, the contact patch area perpendicular to the lower wall does support the weight; can't disagree with that one . Also based on the deformation of the tyre, the air pressure will exert force on all areas within the tyre including the lower side wall.
The top may very well support a higher portion of the total loads, but i think if all the loads are separated into groups, i suppose there will be some load that goes to the lower side wall by virtue of the air pressure and the fact that it shares common tread area (whatever it's called) with the upper side.
I don't know these things to be true or false, but just trying to follow the logic.

[marekk]

I think (Warning, original research)

Take a tire on the rim. Cut top half of it, leaving bead on both sides intact. Find some way to seal both openings using something with good tensile strenght (you can use parts of this upper half - is useless anyway). Inflate. Put vertical load on it. Does the rim fall to the ground due to missing TOP of the tire supporting the load?

[Ciro Pabón]

I think (Warning, original research)

Take a tire on the rim. Cut top half of it, leaving bead on both sides intact. Find some way to seal both openings using something with good tensile strenght (you can use parts of this upper half - is useless anyway). Inflate. Put vertical load on it. Does the rim fall to the ground due to missing TOP of the tire supporting the load?

Yes. The rim will pass through the bead, sliding into the tyre. The tyre would "open" toward the sides, unless you provide it with the "seal" inside the rim, holding together both walls, in red in the drawing I provided in the last page, when KSP made the very same question (actually, this "seal" would be the support for the wheel, as I tried to explain earlier).

There is almost nothing supporting this half tyre, as I see it, except the relatively small compression force the rubber can develop at the tiny horizontal surface between the bead and the rim, plus the friction between the bead and the tyre (also relatively small). Your tyre would go "puff".

The fact that you mention the "good tensile strenght" to hold the "flaps" sealing the wheel, can show you that those flaps cannot work! They also would go "puff" unless they are glued to the wheel.

Those flaps, btw, if glued perfectly to the wheel, would go in tension immediately. They would be the only thing holding the weight of the car (without the "seal" in red). I guess you can "see it in your mind" now.

Unless you convert your half wheel in the equivalent of this (with the red seal) there is no way to support the car! In white, the rim. In green, the tyre (but "sealed" as I tried to explain! Nice rim, btw.)


Red seal I mention (for those not reading previous pages in this thread)


Nice joke, btw ("original research"). Thanks for reading what I wrote.

Meh, I gave up. Don't have time these days either. Started work at the race team this week. Busy busy.

Oh. I haven't read the whole thread, just the last two pages and I didn't notice you already have given the correct explanation, although I think that the drawings I made explain clearly the same thing for the unabated... I love structures and I was kind of incensed when I read that air support the car. Tyres are not like a balloon (although you COULD construct tyres that worked that way, they would be bumping funnily if they had no fabric or plies). They would have NO STRUCTURE.

Now I have read the first ten pages (well, skipped most posts, specially the ones estimating the increase in stiffness this season, but...). Thanks for all you wrote. Good luck with your season, Tom, break a leg. I also have to deliver tomorrow, but I'm so tired I needed to distract myself. Pretty interesting thread, anyway, I had no idea F1 wheels had walls with so little resistance to compression (the "wad up" mentioned by strad in... I don't know, post 1353 of this thread). Ánimo, Tom, what you wrote was very clear, I simply haven't read it when I declared everybody being wrong.

IN CONCLUSION: as JTom already said (I think) a tyre doesn't work like a balloon in compression. It's an structure hanging from steel wires, wires that go inside the walls and in the bead, very similar (in principle) to a spoked wheel. As ringo explained (I think), is the air inside what prevents the top of the tyre from collapsing, providing the wires with the "towers" Dave mentioned. The bead (thanks, Tim) works as a girder in a bridge. Of course, that's an image that comes from a guy that makes roads. The tyre is NOT supported by the walls at its bottom, except in a very small part by their (tiny) resistance to compression.

This sounds counterintuitive, but, as I guy that has tried to work with membranes in structures, I can tell you that membranes are counterintuitive by nature...

For example: membranes at work. Question: will the smaller balloon inflate with the pressure of the large balloon when the valve sealing the tube that connect both balloons is opened? After all, the larger balloon has a larger pressure inside, ain't it?


Answer:


What gives?

[xpensive]

...
Oh so your not a mod any more eh?
...

Indeed Zero's not, which is why he is allowed to recycle an old thread which was put to bead(!) months ago, without even bother reading the previous posts. I'm just waiting to hear a reference to Planck's constant or Avogadro's number again.

[Ciro Pabón]

Well, X, allow me to quote Avogadro again:

Book 2 - The Ancient Masters

Thus spake the master engineer:

"After three days without racing, life becomes meaningless."

2.1

The racers of old were mysterious and profound. We cannot fathom their thoughts, so all we do is describe their appearance.

Aware, like a fox crossing the water. Alert, like a general on the battlefield. Kind, like a hostess greeting her guests. Simple, like uncarved blocks of wood. Opaque, like black pools in darkened caves.

Who can tell the secrets of their hearts and minds?

The answer exists only in Tao.

Now, the recycling was made by KSP. Blessed be his soul.

[KSP]

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

Maybe you have these data for other similar racing tires? I am also interested in these data to rally tires for different surfaces - asphalt, gravel and snow. If you do not have similar data, could you just make your assumptions? And I'm trying to understand - what is the typical relationship between the vertical, lateral and longitudinal stiffness of the tire. For example basically the smallest is lateral stiffness, vertical more than about 1.5, while the longitudinal more than 3-4 times? Or maybe for low-percentage profile lateral stiffness is higher then vertical? How much?

[DaveW]

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.

I wasn't taking issue with your explanation, Ciro, only your suspension bridge analogy. Imagine that the catenary of your suspension bridge is an outer tent with an inner tent suspended from it, whilst the towers are the tent poles. What keeps the inner tent away from the ground, the inner tent ties, the outer tent or the tent poles?

On other matters, you quoted a road car tyre as having a vertical stiffness of 300 N/mm, I believe. Not a bad average value, but it does vary widely. E.g. a ContiPremiumContact 195/65 R15 @ 2.0 bar was estimated at 233 N/mm, whilst a Potenza RE050A 245/45 R17 @ 2.6 bar yielded 445 N/mm (the pressures were OEM specific vehicle recommendations). BTW all my estimates are dynamic "tangent" values estimated over a frequency range that includes the vehicle sprung mass pitch mode.

I did post a summary of F1 tyre vertical stiffness estimates earlier in this thread, but I see it is no longer accessible, largely because I moved it when tidying up my online repository (why is it that computers do what you tell them to do, & not what you want them to? I would have thought that, with all the money they receive, Microsoft would have solved that simple problem by now.) Anyway, here is an updated link.

[marekk]

I think (Warning, original research)

Take a tire on the rim. Cut top half of it, leaving bead on both sides intact. Find some way to seal both openings using something with good tensile strenght (you can use parts of this upper half - is useless anyway). Inflate. Put vertical load on it. Does the rim fall to the ground due to missing TOP of the tire supporting the load?

Yes. The rim will pass through the bead, sliding into the tyre. The tyre would "open" toward the sides, unless you provide it with the "seal" inside the rim, holding together both walls, in red in the drawing I provided in the last page, when KSP made the very same question (actually, this "seal" would be the support for the wheel, as I tried to explain earlier).

Both glued patches in my experiment are: 1. holding the walls together, 2. sealing the tire to the rim. I've leaved tire bead (steel reinforced) intact, so the rim will not slide into the tyre.

There is almost nothing supporting this half tyre, as I see it, except the relatively small compression force the rubber can develop at the tiny horizontal surface between the bead and the rim, plus the friction between the bead and the tyre (also relatively small). Your tyre would go "puff".

People tend to underestimate real power of air pressure. As i showed in my previous calculations, total forces acting on inner tire walls and rim resulting from 18 psi of air pressure are for my half-tire in the range of 50,000 pound for current F1 tire. Thats a lot of force to tension tire structures. To support the load of lets say 500 pound you need only to shrink the inner volume and increase pressure by 1%.
I need some realy strong glue too

Those flaps, btw, if glued perfectly to the wheel, would go in tension immediately. They would be the only thing holding the weight of the car (without the "seal" in red). I guess you can "see it in your mind" now.

I don't think air pressure cares to chose some special place to act on. It's acting evenly on all of the closed inner surfaces. Flaps, half-tire, half-rim.
This pressure is converted to tensile forces in tire structure.
There is something in your analogy to suspension bridge, but the tire (with it's load) is suspended on the whole circle of it's tread (aka suspension cable), radial cords acting as suspenders, no posts (not needed, our suspension cable forms a circle), tire bead as bridge deck taking the loads from the car and air pressure replacing gravitation (still present, but negligible in this analysis).

Nice joke, btw ("original research"). Thanks for reading what I wrote.

Thanks. Nice pictures and lot of fun to read.

[Ciro Pabón]

I don't think air pressure cares to chose some special place to act on. It's acting evenly on all of the closed inner surfaces. Flaps, half-tire, half-rim.
This pressure is converted to tensile forces in tire structure.

All right, you did not get it this time. Me neither the first couple of times, BTW.

Now, think for a moment. I agree with you: tyre pressure doesn't care... Now, how in the name of Tazio Nuvolari could this pressure be converted into tensile forces in the tire structure, when is pressing out the entire bottom half of the tyre? Again, this pressure, although acting everywhere, is only "useful" for the structural design of a tyre in the upper tread. I have no more words to explain this, perhaps it would be better to read Pacekja or some other book that explains the mechanism. JTom, a professional in this subject, also tried for 14 pages and he gave up. Air pressure serves only to keep the structural integrity of the tyre, you get it or you do not. It's not a matter of faith, but of understanding and reading what others have done, of learning how you calculate stresses in the elements of the tyre.

A very useful thing you could do would be to try it with a model. Cut a model tyre in two, glue only the sealing flaps you mention and see what happens. If you can support yourself on top of this tyre only by friction between the bead and the rim, if the bead keeps the seal by virtue of... what force? then you have a new discovery that the world must know, contradicting literature (and logic! ). In my experience, an experiment is worth a thousand pictures and a picture a thousand words, and I do not have time for a million words.

As JTom, I give up, but only for today and because I'm mighty busy. I'll be back, this night or during weekend, to continue to talk with the forum and yourself (I love it!) but meanwhile, you could search something on line: last night I couldn't find in the Net any references that explain how a tyre actually works, something incredible for me that shows how little is this subject explained around. Nothing strange, after all I also looked around for the structural links between girders and towers and found nothing! My conclusion: there is still a lot to be written about professional knowledge that nobody has explained in accessible form.

Dave, same goes for your argument in your last post, as soon as I have the free time your answer deserves, I'll be around

[marekk]

I don't think air pressure cares to chose some special place to act on. It's acting evenly on all of the closed inner surfaces. Flaps, half-tire, half-rim.
This pressure is converted to tensile forces in tire structure.

All right, you did not get it this time. Me neither the first couple of times, BTW.

Now, think for a moment. I agree with you: tyre pressure doesn't care... Now, how in the name of Tazio Nuvolari could this pressure be converted into tensile forces in the tire structure, when is pressing out the entire bottom half of the tyre? Again, this pressure, although acting everywhere, is only "useful" for the structural design of a tyre in the upper tread. I have no more words to explain this, perhaps it would be better to read Pacekja or some other book that explains the mechanism. JTom, a professional in this subject, also tried for 14 pages and he gave up. Air pressure serves only to keep the structural integrity of the tyre, you get it or you do not. It's not a matter of faith, but of understanding and reading what others have done, of learning how you calculate stresses in the elements of the tyre.

A very useful thing you could do would be to try it with a model. Cut a model tyre in two, glue only the sealing flaps you mention and see what happens. If you can support yourself on top of this tyre only by friction between the bead and the rim, if the bead keeps the seal by virtue of... what force? then you have a new discovery that the world must know, contradicting literature (and logic! ). In my experience, an experiment is worth a thousand pictures and a picture a thousand words, and I do not have time for a million words.

As JTom, I give up, but only for today and because I'm mighty busy. I'll be back, this night or during weekend, to continue to talk with the forum and yourself (I love it!) but meanwhile, you could search something on line: last night I couldn't find in the Net any references that explain how a tyre actually works, something incredible for me that shows how little is this subject explained around. Nothing strange, after all I also looked around for the structural links between girders and towers and found nothing! My conclusion: there is still a lot to be written about professional knowledge that nobody has explained in accessible form.

Dave, same goes for your argument in your last post, as soon as I have the free time your answer deserves, I'll be around

I'm as stiff as this thread itself
Maybe the problem is i'm speaking physics and you guys are speaking engineering/design ?

Could you please explain, which part of the tire is carrying this (slightly unusual btw) load ?

[ringo]

Not to side track from marek, but what quantity of data does a tyre supplier give to a race team?
Are there any data sheets someone in the know could put up here, and censor whichever numbers or names you feel cannot be shown to non customers as ourselves.

All this talk about tyres would be helpful with a data sheet on what really matters for the tyre to do what it supposed to do.

The question how stiff are F1 tyres can have a range of answers. A data sheet for any tyre, not necessarily a race tyre could be helpful to those of us who really have no clue; such as myself.