How stiff are F1 tyres?

[Ciro Pabón]

After 18 pages, people still aren't getting it.

I'm convinced people love to hear the sound of their own silly debate. Not even debating the same thing. Like having one person say, "Platoon was the best Vietnam movie," and the other respond with, "I disagree. Stolichnaya is the best vodka."

Ridiculous.

Well, I disagree... The answer to that question is: "Because it can produce a few notes, though they are very flat; and it is nevar put with the wrong end in front!"

Just joking.

I cannot avoid thinking on another old joke, about the question in the engineering exam:

Describe the Universe in 200 words and give three examples.

Now, seriously, I think that the need for interaction drives forums and that is not ridiculous at all, but an expression of friendship and camaraderie that is moving humankind ahead. So, let's talk.

In the end we will learn when we bump into the correct answers, at some point in our lives.

You know, when suddenly things click.

That is, unless somebody with the knowledge point the people to the good literature. Ehem.

Another thing I find surprising is the need for knowledge. According to Cicero (De officii, On Duty), is one of the four things that move men toward honour.

... Thus we come to understand that what is true, simple, and genuine appeals most strongly to a man's nature.

To this passion for discovering truth there is added a hungering, as it were, for independence, so that a mind well-moulded by Nature is unwilling to be subject to anybody save one who gives rules of conduct or is a teacher of truth or who, for the general good, rules according to justice and law.

From this attitude come greatness of soul and a sense of superiority to worldly conditions.

So, if you're a teacher of truth, some "well-moulded minds" will hear you, do not despair, JTom.

I'll never forget the day I taught 10 years old kids how a bridge worked (it's not what I explained before, it is how a bridge ACTUALLY works, we did it with a sheet of paper and it's not THAT simple as you're thinking). They were so excited!


Two of them declared, on the spot, that they wanted to build roads and bridges when they grew up. I hardly was able to contain the tears, just seeing how they seemed happy.

Have you ever thought, JTom, that people could be so excited about your profession? Well, man, they are. We need to know, and I find that characteristic of the human soul a thing of beauty... combined with independence, as Old Cicero says.

... and Ron Viejo de Caldas is the best rum, don't be ridiculous.

[marekk]

Contrary to JT, i find our speculations really funny, so let's continue:

Let us start with a tire with solid, steel reinforced bead, but made of thin, high-elasticity ruber - sort of baloon. Inflate it. Apply some load. It will fall to the ground.
Not good.
Now start to reinforce your tire with very thin plys of reinforced rubber (still elastic, but real world, so not linear) and add some pressure till it just does carry your load. Look at it. Except for contact patch area - near perfect, slightly blowed up, flat bottomed tube. All the way round, not just on top.
How it works ? Obviously your load is changing tire's shape, volume, air pressure, increasing elasticity forces in all of your tire's structure (tension), vector sum of those forces reacting your load.
Try do add some pressure. Does your rim go a liitle up ? Does it feel a little bit stiffer ?
Now continue, until you get a tire ready to go without air pressure at all.
You can add some extra reinforcement to tread area, to get better shape. Congratulations - you did you very own flat run.

My question to wise man's is - at wich moment our experimental tire stoped to change inner pressure under load and started to support it just form reinforcement tension at the top ?

[DaveW]

Now I feel a bit of a heel, Marekk.

18 psi is not a million miles away from a race tyre pressure (cold, perhaps), but it is 18 psi gauge (i.e. 32 psi absolute, using your value for atmospheric pressure).

The total pressure acting on your body multiplied by your surface area may yield a number of 17,000 kg (I've not checked), but that isn't going to hold you up, down or push you in any other direction, because the resultant pressure-induced force acting on your body is zero. The same is true for a wheel, and for a tyre - when it is not in contact with anything, anyway.

Now, when the tyre is in contact with a flat surface & a load is applied to the wheel axle, the wheel will deflect, of course. To first order, however, the enclosed volume will remain unchanged - air will simply be pushed around inside the tyre. In truth, & in fine detail, the enclosed volume might decrease a little when a load is applied which would increase pressure slightly, but this will not unbalance the pressure distribution acting on the wheel. Hence the air itself cannot transmit any component of an applied force between the tyre & the wheel rim.

Apologies, Marekk.

[marekk]

Now I feel a bit of a heel, Marekk.

18 psi is not a million miles away from a race tyre pressure (cold, perhaps), but it is 18 psi gauge (i.e. 32 psi absolute, using your value for atmospheric pressure).

The total pressure acting on your body multiplied by your surface area may yield a number of 17,000 kg (I've not checked), but that isn't going to hold you up, down or push you in any other direction, because the resultant pressure-induced force acting on your body is zero. The same is true for a wheel, and for a tyre - when it is not in contact with anything, anyway.

Now, when the tyre is in contact with a flat surface & a load is applied to the wheel axle, the wheel will deflect, of course. To first order, however, the enclosed volume will remain unchanged - air will simply be pushed around inside the tyre. In truth, & in fine detail, the enclosed volume might decrease a little when a load is applied which would increase pressure slightly, but this will not unbalance the pressure distribution acting on the wheel. Hence the air itself cannot transmit any component of an applied force between the tyre & the wheel rim.

Apologies, Marekk.

My fault - but that means forces are even stronger and changes resulting from 185 kg load harder to see and meassure.

I'm afraid, enclosed volume will not remain unchanged.
Under static pressure, tire's internal shape is already as ideal (max of area/volume) as possible. Every change in shape resulting from your load will decrease volume (to first order, we don't take into account change of tire's area resulting from elasticity).

Decreased volume means increased pressure, acting perpendicular to tire's (and rim's) inner area, trying to blow it up. And it blows it up, very, very slightly due to high young modulus of reinforced tire. New equlibrium is more air pressure and more tension in fabric counteracting it.
Vector sum of this tension acting on both sides of the rim supports your load.
Air does transmit load to the rim through the tire's structure.
Air does not transmit any load to the rim directly.

[Ciro Pabón]

All is good and very reasonable.

So, if tyre pressure changes in a significant way under load, as you should assume in the case the air is sustaining the load, here you have a recipe to change a spare tyre:

1. Inflate spare tyre at correct pressure. Put spare in trunk.
2. When your car has a flat tyre, remove flat tyre and put spare tyre in place.
3. Deflate spare tyre to correct pressure, because under load, the pressure inside has increased in a significant way. An alternative would be to inflate spare tyres only under load.

I wonder why manuals do not give you that recommendation. They all must be wrong... Anyway, from now on, I know what to do: every time I put a spare in my car, the first thing to do is to deflate it. Please, don't call me genius, although I know I deserve the title. I am a very modest guy (and I have the titles that prove it: "most modest guy in the Universe").

I find also in this idea a new way to correct the problem of tyres with low pressure.

1. You notice tyre is deflated.
2. You increase the load of your car. The pressure inside the tyre increases because of the increased load.
3. There is no step 3, because the problem is already fixed.

This gives me a new idea for service stations. Instead of air pumps, they could sell you a few hundreds kilos of lead to put in the trunk when your tyres lose pressure. Of course, as the sidewalls are taking part of the load, let's say 50%, you should double the amount of lead for the pressure to recover its original value. As the lead can be recycled, we will save a lot of money in electricity to power the pumps. You also do not need manometers: you simply keep adding lead until the tyre recovers its shape.

Another idea: instead of spare tyres, taking space in the trunk, we could put anvils on the side of roads. As soon as you notice a tyre is having lower pressure, you put the anvil in the trunk. The increment in pressure could be enough to arrive to the next service station. BTW, I've seen ACME brand anvils that could be useful for this purpose, specially in the desert, where service stations are few and (if you trust Wilie Coyote) ACME anvils are abundant...

I also have devised new road signs to be put in docks and delivery warehouses around Colombia. It says: "All trucks must deflate tyres as soon as they are loaded and inflate tyres when unloaded". I'm sure truckers will get the point soon: they will save a pile of shite in gas costs, because we all know how important is to keep constant pressure in tyres to save gas.

This change in pressure is VERY important as a truck, that weighs 20 tons, can carry 40 tons. I think I have noticed how tyres get taller in loaded trucks because of the increment in pressure and how, when unloaded, they automatically get flatter because of the decrement in the inner pressure. We are talking here of a 200% increase in load, guys. Haven't you noticed this effect? No? Oh, c'mon, don't play jokes on me. I have plans to baptize this the Zero Effect (don't you get it? Zero, Ciro, sounds the same. Ha, ha! How funny I am!)

Tomás, my son, after reading all that, said I should call it Reductio Ad Absurdum instead of Zero Effect, but you, frequent readers of F1Tech, know how this kid is: he is a cynic and he's only 11. Besides, I don't understand him when he speaks French and, if you believe JTom, nobody does.

QED.

[ubrben]

I don't think you can separate the two. The air pressure creates the cord tension that carries the load. But the tension is proportional to the air pressure, so it is the cord properties plus the air pressure that is important.

The same tyre with more air pressure has more load capacity.

Ben

[Ciro Pabón]

So, if I use twice the air pressure I can carry twice the load?

My mistake, thanks a lot. I did not realize I was separating the two. I mistakenly thought I had said something like "is the air what tensions the tread" like five pages ago in big bold letters, but maybe what I wrote was that "is the air what tensions the thread". There is a BIG difference between those two phrases. I can see the extra H, a letter than in Spanish is not pronounced at all. An EMPTY letter, so to speak.

So, Ben, I have been enlightened. I have a car with a carrying capacity of 1 Ton.

You gave me this great idea: as I wish to carry 2 Tons, I will inflate my tyres (wich are rated for 32 psi) to 64 psi.

I don't care if the springs are fully compressed and the maker of the tyres explains patiently that if I overinflate them by only 6 psi, I can damage the wheel hubs. Why are they talking about the hubs and not the treads? The morons!

But wait, there is more. (COMPLETELY FREE! Call now! Operators are standing by).

Actually, I will buy the tyres that can hold the LARGEST pressure possible. For example, my car has a "donut tyre". You know, those spare tyres that work at 60 psi.

So, I will use those 60 psi rated tyres instead of regular 32 psi boring tyres and, from then on, I can carry more load. Wonderful idea. Who cares if those tyres are tiny? As they have more pressure inside, surely I can carry more load with them.

I feel soooo secure with my car using four of these emergency spare tyres and carrying 1.900 Kg!

This car is ready to carry more load! Almost twice the load at twice the pressure! Don't you feel safer, knowing that with a higher pressure you can load this thing A LOT? These tyres HAVE to be inflated at 60 psi, so they will NOT burst.


Now, I have another question: if I plan to run my car at 270 kph, those pesky racers (you know, the ones that ACTUALLY have experience) tell me I have to overinflate my tyres by 7.5 psi AND then I need a car 15% lighter. How stupid they are! Everybody knows that the more pressure, the more load I can carry because is the air inside what carries the load! Can you figure out why they are so dumb? I do not want to read ANYTHING on the subject, I find it boring, so I can go through life, confident in my own reasoning.



They must be wrong. After all I have a very solid argument. I call this engineering: the art of being stubborn until I discover how to tire (ha, ha! Am I funny or what? Get the pun? Tire, tyre) other people that explains to me "their truth", that, as we all know, is purely relative, like in literature, art or any other social science. Actually, I will baptize this as Zero Engineering, to have a Corporative Image (Zero Corporation, the fathers of Zero Engineering and Zero Effect).

I think I will hire Wilie as my copilot, the guy clearly knows what he's doing. HE surely is PERSISTENT, and when he falls from those cliffs he escapes unhurt. He has a thick head, I bet, that's what saves him. Besides, he ALWAYS find the mistakes in Roadrunner first escape and acts accordingly, changing slightly his traps, to catch the Roadrunner the second time around.

Beep, beep.

[marekk]

Ciro,

funny to read as always, but just for your son, to let him now as our universe really works:

OK kids, back to the roots. Physics class, lession 2: (lession 1 was about m,s,kg,K) Conservation of energy law.

Lab setup:

1 x slightly modified F1 car (we have replaced all suspension springs with solid, almost uncompressible tubes (titanium of course, it's F1 car). I take Renault's R31 - nice looking and should be Robert's car this year, and i like this boy a lot (it's my countryman, i have to), even if he publicly say's, he doesn't know how are his bones build, but he don't care.
4 x xslightly modified pneumatic tire's (you guess it - almost infinite Yuong modulus of tire's and rim's structure/reinforcement, very, very low elasticity, but strong - carbon nanotubes will be something we can use, money's no issue).
2 x mechanics.

Experiment:

Car (640 kg) with all wheels attached heaved up by 2 mechanics using usual equipment.
Green light, mechanics begin to lower the car. We stop at the very moment, as wheels are just touching tarmac, cars center of gravity at some 55cm hight.

What's total energy of this car at this moment ? Appart from energy/mass equivalent (you know, this funny e=mc^2 equation), it's just potential energy in gravitation field of our universe. We leave all of this universe in peace, and take only earth's gravitation into account, resulting error doesn't seem to be to generous. So we have just E=mgh1.

Now let mechanics lower it further and have some launch.

All tire's slightly flatter, so car's center of gravity now at 50cm, and we have only E=mgh2 < mgh1.

Where's 10% of our energy gone ?

Let's start to investigate.
What have changed from h1 to h2 ?
Car itself ? dosesn't look so.
Rim? either.
Tire's structure ? Shape is changed, but can this structure without any elasticity store energy ? In what form ? Think about it. Twice.
Soul of the tire ? could be, i've read somethimg about expermients on dying man's weight, resulting in human's soul weight at about 2g. But tire's don't have soul and this one isn't dying (yet) either.
One more look. And one more to be sure.
Dammed, it have to be this air inside. Slightly warmer and slightly more compressed to accomodate our missing energy.

Now, as we don't trust anyone who didn't read almost any engineering manuals, paceka included, we have to proof, if this energy is really in our tire.

Turn your lightsaber's on, padavans.
Quickly cut all 4 wheels free (be carefully).
Do you see those 4 bouncing wheels ? Bouncing against our gravitation, against atmospheric air's viscosity, transfering part of it's energy to heat at every contact with tarmac due to internal frictions ?

Anyone to argue against consevation of energy law ?

{Moment of silence, applause}
End of lession 2.

Now as we are a little bit wiser, we can replace our titanium tubes with springs and our wheels with real wheels and take a look.
What's changed ?
Part of our petential energy goes to suspension springs, part of it goes to air pressure, another one is stored in structures elastic bondings, small part is converted to heat due to frictions and air pressure change.

What we learned is, i think, NEVER BET AGAINST AIR PRESSURE.
Very usefull if you are going to scuba dive, btw.

And you don't have to double your pressure to be able to take double the load. For your 1000 kg car, tire's internal pressure/load increase resulting from your cars weight will be less then 1%. Just take some time to read our previous posts.

[marekk]

Now, as we know how it works, let us go back to the topic.
We can try to undestand F1's tire stiffness based on pure physic and mathematic.
Should not be that hard.
What we have to consider:

Volume change with geometry change (not linear in any way)
Pressure change with volume change (not linear)
Tension change with pressure change (not linear)
Inner area change with tension change (not linear)
Temperature change.
Speed of sound in compressed air (our pressure change is not instant, in fact it's forming a wave going through tire with the speed of sound).
Speed of sound in tire's structure (the same as previous)
Friction forces in tire's structure (very, very nonlinear).
Friction forces between tire and tarmac.
Static and dynamic external air pressures.
Lateral and radial centrifugal forces.
Internal air's centrifugal forces, with special attention to boundary layers.

Let's not forget, that all of above are dependent on each other.

We don't want at the moment to go into details, so we leave quantum mechanics phenomena and indivudual subatomic forces out of our investigations.

Anyone with good math skills ?

[ringo]

I don't think you can understand it without having the data. It's something that either requires multiple models or experimental data.
What we do know, as fact, is that varying the inflation pressure affects the static, dynamic and rotating dynamic stiffness.

What we don't know is how stiff the F1 tyre is and how it reacts to inflation pressure changes.

Jersey Tom, spill the beans.

Put it on wikileaks if you have to

[marekk]

I don't think you can understand it without having the data. It's something that either requires multiple models or experimental data.
What we do know, as fact, is that varying the inflation pressure affects the static, dynamic and rotating dynamic stiffness.

What we don't know is how stiff the F1 tyre is and how it reacts to inflation pressure changes.

Jersey Tom, spill the beans.

Put it only wikileaks if you have to

I don't think you can understand it even having this specifications. Looks really complex to me.
That's what all teams are doing at the moment: collecting data, improving correlations between numerical models and real thing, trying to get some understanding of tires behavior to the point to be able to make some (i.e. setup) predictions from it.
I doubt they want to share those informations with anyone, tire being biggest single performance factor for the cars.

[strad]

[DaveW]

End of lession 2.

It follows, of course, that the tweel picture posted by Ringo is a fake. It couldn't possibly support a vertical load.

BTW, Ringo suggested that the spokes of the tweel replace the pressurised air in a pneumatic tyre. The fact that most of the spokes are in tension (according to my thought experiment) questions the validity of that idea.

Ben: I don't think anybody has denied the importance of air pressure in determining the properties of a pneumatic tyre. I'm not anyway. However, it has been argued that contained air pressure increases as load is applied to a tyre, and it is the increase in air pressure that "carries" (or reacts) the load. That is the thesis I question.

[Jersey Tom]

Have you ever thought, JTom, that people could be so excited about your profession?

I did get that impression... given that it's why I was able to get a new job

What we don't know is how stiff the F1 tyre is and how it reacts to inflation pressure changes.

Jersey Tom, spill the beans.

Put it on wikileaks if you have to

Think the beans have already been spilled. You have two tire engineers in this thread that have tried describing it. Well.. one active tire engineer and one former!

The actual numerical spring rate value isn't important. As for what air does... I thought Ben put it pretty well. Spring rate is going to be directionally proportional to inflation pressure. More air pressure -> more cords tensioned -> higher spring rate. The important thing is that the cords carry the load in an inflated tire. Without the air to preload the cords, you're relying on whatever mechanical stiffness is there, which ain't much (run-on-flats excepted).

Let's review - the whole point of the carcass cords in a pneumatic tire is to carry the load (which is supporting the rim). The rim does not ride on the air itself - it can't since the air pressure acts equally on it in all directions.

This is completely different from what happens when you get on an air mattress, since in that case the thing is underneath you. If you were to go inside the air mattress (presuming it's pretty damn tall) you'd fall to the bottom of it since the air pressure acts on you equally in all directions and cannot support a load.

Notice a similarity? Same thing as the rim of a car effectively being "inside" the tire, or at least having the tire inflation pressure acting equally on the rim.

As an aside... are F1 tires very stiff laterally? In a mechanical sense, absolutely not (we can all reference the pictures of uninflated Bridgestones being wadded up). If someone were to cut a slice through one, I bet you'd see that the sidewall of the thing is incredibly thin. Probably less to it than the tires on your parents' minivans.

Do they have a high response rate? Hard to say. I don't even know for certain as my previous employer had been out of F1 since before I hired in. There is some supposedly representative F1 tire data in RCVD. By themselves I don't think the tires are that incredible. They're almost forced not to be, for reasons I can't get into, but could probably be way higher. IMO the thing that gives F1 cars their incredible responsiveness is the downforce - it "cheats" up the tire response with no increase in inertia.

[DaveW]

Nasties called JT? I hope that works for you. If you encounter LenD, say hello.