How stiff are F1 tyres?

[marekk]

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.

Why couldn't it support a vertical load ?
I see no problem from the energy point of view.
All of this energy in Tweel is stored as elastic energy of Tweel's structure, mostly working by tension with some small part in compression.
And in pneumatic tire it's air + elasticity. You can't say it's just air or it's just structure. It's both.
Tweel supporters replace both air and sidewalls of convetional pneumatic tire.

[marekk]

Not exactly F1 tire, but i think pretty close (it's NASCAR).


As mentioned by JT, at those speed's you have to be very carefully with tire's weight - at 360 km/h 26" wheel rotates 50 times a second, centrifugal forces and momentum will be huge.
Just +1 kg of rubber on tire's tread results in +30,000 kg of centrifugal force at this speed.

[DaveW]

...And in pneumatic tire it's air + elasticity. You can't say it's just air or it's just structure. It's both.
Tweel supporters replace both air and sidewalls of convetional pneumatic tire.

Thank you Marekk, I'm almost happy......, except that the structure of a pneumatic tyre always supports all the applied load. Changing the pressure of the air in the tyre can modify the shape of the tyre and will change the tensile "preload" in the structure (& hence change elemental stiffness since tyre structural elements have non-linear properties). Both will normally change the vertical stiffness of the tyre.

Whether the internal pressure changes when the tyre is loaded, & whether that is significant, is a moot point (I think it is not significant, based on many observations). If is does (& is) then that is certain to be tyre-dependent. May I remind you that I have found that increasing tyre pressure does not always increase tyre stiffness. Some tyres, quite consistently (at least under rig test conditions), will increase vertical stiffness as pressure is reduced. I guess that would be lesson 9 & 3/4..... (but think shape changes vs preload changes).

[DaveW]

Not exactly F1 tire, but i think pretty close (it's NASCAR).

Now I know you are playing with us, Marekk....

[ringo]

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.

I don't dispute that the cables carry the tension, if you read my posts. my arguement was that the tension is provided by the air, so the air is responsible really for carrying the load.
Initially it seemed as if Ciro and Dave were saying that the air has nothing to do with the load carrying or the vertical stiffness. After clearing their opinions i have nothing to argue argue really. I found that famous tyre book and posted some pretty insightful graphs, so that issue is cleared.

[marekk]

My last (i promise!) attempt to convince Dave:


lips = air
string = tire
arrow = rim

I think lips do play some role for this bowl.

As for stiffness increasing on pressure decrease: it's a question of geometry and used materials.
I'm quite sure, that total stiffness of this tire increase with pressure, but you can design it to have some nonlinearity between for example vertical and lateral stiffness. You can build (just my imagination, no idea if it's used in real world) some pre-tension in your tire, so this pre-tensioned part will change tire's shape change versus pressure compared to a tire without this. I'm not good at drawing and i don't think tensor calculus equations will clarify it any better for us, so i suppose let us go further with the topic of F1 tire's stiffness based on engeenering models. The tires on our cars are designed this way and are good enough to drive us every day to work

[Jersey Tom]

Not exactly F1 tire, but i think pretty close (it's NASCAR).

Now I know you are playing with us, Marekk....

I'd imagine NASCAR and F1 tires are probably pretty similar in some respects. Drastically different in other specifics of course, but I bet if you cut open a Bridgestone F1 slick it wouldn't look much different from that photo.

To Ringo's comment... it is partially semantics, but I would still not say the air is responsible for carrying the load. In that verbiage it sounds like the air is some sort of load-bearing item.

Could think of it this way... if we were describing a house, and asked what is responsible for carrying the load of the roof, what would we say? The answer is the walls and framework inside them. We wouldn't say that the carpenters are responsible for carrying the load, even though without them the walls and framework wouldn't be there (much like without air inflation, there wouldn't be the cord pre-tensioning required to support the rim).

[ringo]

The air is actively supporting the tyre wall and the belt.

The air is a load bearing item, even though it's not a solid. If a tyre deflates and the car goes to the ground the only thing that changed was the reduction in air pressure. The wall structure does not change so the air was responsible for the reduction in support.

A good visualization is thinking of the tyre as a hinged floor.
The floor will droop and hang off the hinges naturally, bringing the hinges in their fully extended position. The hinge has to be perfectly vertical to transmit the load and support it, when the floor is falling and the hinge is not vertical, nor force is being transmitted.

The only way a bent hinge will transmit the load is if it is buttressed by a horizontal force. This force is provided by the air pressure and is not equal to the full load going through the hinges.

Another example i have is the very same thing concerning what supports the tyre, even when the cables are working full time holding up the bead.

I don't have to explain this one, since we all know a curved strip can't support 4000lb car.
And see that i have my cables holding up the rim. The thing that is holding up the cables is the belt and the thing that is holding up the belt to stabilize it and provide a path to transmit load to the ground is non other than the air pressure.



if this is not the case feel free to explain the last drawing. What gives the band it's shape and stability. And don't look to the cables under the rim taking a comrpession laod.

[marekk]

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.

Since there is no more competition between tire suppliers in F1, there's no point to make it any better then requested from FIA at bid time.
Tires are free and the same for all the teams, so you can't make more money for better tire, and from marketing point of view you have only to make sure your tires do not explode every race in front of TV watching crowd.
If you make it 2s a lap quicker, nobody (apart from hard core fans like us) even notices.

[Jersey Tom]

I meant f1 tires in general by any manufacturer

[Mystery Steve]

This thread reminds me of a Mitch Hedberg joke: "My belt holds my pants up, but the belt loops hold my belt up. So which one's the real hero?"

To be honest, I'm not sure why the discussion keeps going. I think it was established a while ago that the sidewall carries the load because it is has applied pretension by the internal air pressure. The concept really isn't that complicated.

[marekk]

This thread reminds me of a Mitch Hedberg joke: "My belt holds my pants up, but the belt loops hold my belt up. So which one's the real hero?"

To be honest, I'm not sure why the discussion keeps going. I think it was established a while ago that the sidewall carries the load because it is has applied pretension by the internal air pressure. The concept really isn't that complicated.

Agree. Pretension applied on inflation time is several orders of magnitude higher then expected maximum load, so for engineering purposes this simplified concept/model works as expected.

[Ciro Pabón]

I'd imagine NASCAR and F1 tires are probably pretty similar in some respects. Drastically different in other specifics of course, but I bet if you cut open a Bridgestone F1 slick it wouldn't look much different from that photo.

Do they use dual tyres in F1? You know, the safety bladders. (I know they are mandatory at NASCAR tracks longer than a mile).



I know that they are a safety feature, but let me ask a couple of questions (well, actually, three of them):

1. Does the inner tyre serve somehow as the inner balloon in... well, Piccard proposed dual compensated balloon? You know, it works as a kind of pressure equalizer. In this balloon, when the outer balloon stretches at high altitude (because the external air pressure drops) the inner balloon, which is a super-pressurized one, also expands, keeping the volume of the outer, zero pressure, balloon more or less constant. Something (although not equal) to Roziére balloons that allowed long duration flights around the world (with a super-pressure balloon on top of a zero air heated air balloon).

2. There is also a difference in volume when centripetal force stretches the two tyres, inner and outer. That's why I ask how they behave. Are the differences in centripetal force enough to be "felt"? Does the outer balloon pressure drops because of that?

3. Finally, has this safety bladder any effect on temperature when the outer tyre heats? The inner one must be cool, because it doesn't flex at all, and probably is able to absorb heat more than "simple" air inside, it has a larger "thermal mass".

I would appreciate any bit of information about that, or any literature (if the effects are noticeable enough for somebody to ponder how it works, I could not find anything).

I know (well, I assume) safety bladders must be a no-no in F1 because of un-suspended mass, but I'm curious. I wonder if they could serve any purpose in F1; after all, there is a memory I have of Mr. Hamilton crashing a couple of years ago in a very bad way because of an exploding tyre...

I also know that in NASCAR (at least at some tracks or during some seasons) they use different compounds for inner/outer tyres. Could they be used in F1? (joke, joke...).



I wonder how they mount the dual tyres and how they inflate them. I've never seen that. You have to check two pressures.

[marekk]

Do they use dual tyres in F1? You know, the safety bladders. (I know they are mandatory at NASCAR tracks longer than a mile).



1. Does the inner tyre serve somehow as the inner balloon in... well, Piccard proposed dual compensated balloon? You know, it works as a kind of pressure equalizer. In this balloon, when the outer balloon stretches at high altitude (because the external air pressure drops) the inner balloon, which is a super-pressurized one, also expands, keeping the volume of the outer, zero pressure, balloon more or less constant. Something (although not equal) to Roziére balloons that allowed long duration flights around the world (with a super-pressure balloon on top of a zero air heated air balloon).

I think they are both at the same (initial) pressure, so this inner one just floats until external one goes to hell. If you change rim construction, you can try to pressurise smaller tire more to change active volume of bigger one.
But hey, Ciro, do you really think this air volume/pressure plays any role after initial inflation ?

2. There is also a difference in volume when centripetal force stretches the two tyres, inner and outer. That's why I ask how they behave. Are the differences in centripetal force enough to be "felt"? Does the outer balloon pressure drops because of that?

Quite sure. Centripetal forces, inertia and gyroscopic effects are all related do the mass of your wheel and quite big at 50 rotations per second. And with this solution you almost double tire's weight.

3. Finally, has this safety bladder any effect on temperature when the outer tyre heats? The inner one must be cool, because it doesn't flex at all, and probably is able to absorb heat more than "simple" air inside, it has a larger "thermal mass".

I think air/nitrogen isn't that good as heat transfer agent. Hysteresis will be quite big. But looking at this picture

you can use this inner tire as sort of heat shield.

after all, there is a memory I have of Mr. Hamilton crashing a couple of years ago in a very bad way because of an exploding tyre...

He crashed due to some excesive heat from the rim, so this shielding effect could help him, but not for very long - probably just to the next corner

[DaveW]

Moons ago, Ciro, I was invited to rig test my first NASCAR. Part way through the test something fairly dramatic happened that caused me to rush around trying to find the transducer(s) that had failed, or become dislodged. After spectating for a while (no doubt with some amusement), the engineers announced that the reason the tyre stiffness had changed so dramatically was because they had adjusted the pressure split of the tyres. Then I discovered the car was fitted with inner liners (which explained, incidentally, why the wheels had 2 schrader valves). So far as I know, NASCAR (& related series) are unique in using inner liners.

I leave you to decide why they changed the pressure split, & what effect that might have on track. I try not to guess the rationale underpinning NASCAR set-ups.