How stiff are F1 tyres?

[alelanza]

... I'm actually surprised to have this discussion with someone who claims to work with tyres, but then again, I never met an engineer who uses both "Planck's constant" as well as "Avogadro's number" in his job?

Easy there x, i think this is a very interesting discussion, no need to disregard people like that. Remember, as much as you got used to it, you're not arguing with WB here, hopefully you're not missing him
I think in the end this comes down to which concepts are being discussed, i for one understand JT's argument quite well, all load must necessarily reach the rim through the sidewalls bead.
On the other hand you're right with the contact patch/pressure thing. I don't see how these two things contradict each other. Perhaps you can explain what it is you have a problem with regarding JT's point?to

[strad]

Air can and does support a load.

[Jersey Tom]

the force between road-surface and tyre will always be air-pressure times contact-patch area.

Unfortunately this is not true. There are some easy ways of proving it while at the racetrack or in the comfort of your own garage.

But I'm not going to bother wasting the time or energy trying to explain this further. Like running against a brick wall. Believe what ya want...

[strad]

OK...and you do the same.

[xpensive]

the force between road-surface and tyre will always be air-pressure times contact-patch area.

Unfortunately this is not true. There are some easy ways of proving it while at the racetrack or in the comfort of your own garage.

But I'm not going to bother wasting the time or energy trying to explain this further. Like running against a brick wall. Believe what ya want...

But I think most members would like to see you prove it here on the board. Try it the old-school engineerish way and identify the forces acting on the contact area between tyre and road surface, it's not quantum physics but it usually works.

[DaveW]

Forgive me, but I think it is time to put this aside to bed. gruntguru explained the mechanism quite intuitively, I think, in the Autosport forum:

"Although true that the load transfers from the "tread-band" to bead via the sidewall, this is accomplished by the entire perimeter of the sidewall ie compression at the bottom, tension at the top, shear at the front and rear and a mixture in areas in-between. The tyre in the "balloon" model probably achieves this mostly in the "shear" stressed areas.

As for air pressure acting evenly around the wheel, it is the air pressure at the very top of the tyre that is pushing up on the "tread band" of the tyre without an equivalent area to balance it at the bottom (the area being reacted by the road surface ie contact-patch)".

Now, X would say (I guess) that this demonstrates that an applied load is transferred to the tyre belt by the pressurized air. JT, on the other hand, would probably say that the air (to first order) was undisturbed by the application of the load, & therefore made no contribution (to the actual transfer of load). Depends which way you like to view it, I suppose.

[riff_raff]

DaveW,

I think this thread is great, and I'd like to see the discussion expanded so that I can learn more about the topic.

For example, besides discussing how the tire transfers static vertical loads, how about an explanation of how the tire transfers side loads, or even how the tire transfers braking/acceleration torques?

The concept of compressive load transfer thru fibers preloaded in tension is a bit counter intuitive. So it makes a very interesting topic of discussion.

riff_raff

[xpensive]

The concept of compressive load transfer thru fibers preloaded in tension is a bit counter intuitive. So it makes a very interesting topic of discussion.

riff_raff

That's a very good point riff, it's a pity this forum's tyre-xpert has given up on us mortals from the Newtonian world.

[Belatti]

You have no idea the pitched battle that I have risen with my girlfriend (she is about to have her degree in physics) discussing this topic.

Two persons with way different university educations that see the same problem with distant point of views. It was a nice thing to discuss.

I think that JT is right, and this last points that Terry brought to the table makes me think that JT is right even more.

Let me say what I think: In a very simplified model with revolution symmetry (and using the 'method of sections' JT mentioned), when you integrate all the diferential forces produced by air pressure times diferential areas you end up with a big 0. The meaning I give to that 0 is that the air does not bear load. It just tenses the tyre walls so they wont buckle...

[strad]

They won't buckle because of the load bearing by the air pressure...the cords, threads and other make up of the sidewall have no real strength,,they are soft as cloth,,,it's imo the air that does the actual supporting and I haven't heatrd anything to change my mind..Air can support and tranmit a load.

[alelanza]

They won't buckle because of the load bearing by the air pressure...the cords, threads and other make up of the sidewall have no real strength,,they are soft as cloth,,,it's imo the air that does the actual supporting and I haven't heatrd anything to change my mind..Air can support and tranmit a load.

It can, but it doesn't seem to be the case for a tyre. Like JT said, all pressures around the rim even out to zero thus air is not transferring the load to the rim. Just exactly how loads get transferred through the pre loaded tyre wall is hard to understand, but it looks like there's no other choice really, unless you see one in which case i'm all ears.

[xpensive]

But nobody ever said that the air pressure is conducting the load directly to the rim, I know I never did?

- What faces the road surface load-wise is air pressure times contact patch area.
- What faces the rim load-wise, is the force from the bead in contact.
- In between the two contacts above, load is conveyed through the sidewalls only.

Conclusively, the way I see this very simple static analysis; The air-pressure indeed carries the load from the road surface, through the sidewalls, to the bead and finally to the rim.

Try this perhaps, fill the wheel of your car with as much pressure as the tyre can handle and notice the size of the contact-patch. Then slowly let the air out and if not completely out on a limb here, I'm certain you will see how the size of said contact-patch area miracleously increases with the sinking pressure before your very eyes?

[Belatti]

They won't buckle because of the load bearing by the air pressure...the cords, threads and other make up of the sidewall have no real strength,,they are soft as cloth,,,.

I have seen a car (with tyres and all) standing on 4 empty soda cans. Soda cans are made of an Aluminum foil that is... "soft as cloth"

How can 4 pieces of Aluminum cloth bear the weight of a car? The same way an egg wont brake when you press it evenly with your hands.

[alelanza]

Conclusively, the way I see this very simple static analysis; The air-pressure indeed carries the load from the road surface, through the sidewalls, to the bead and finally to the rim.

I guess the devil is in the 'through the sidewalls' bit. Air pressure is acting normal to the sidewall, so when you say'through' I have a problem understanding what you mean

Try this perhaps, fill the wheel of your car with as much pressure as the tyre can handle and notice the size of the contact-patch. Then slowly let the air out and if not completely out on a limb here, I'm certain you will see how the size of said contact-patch miracleously increases with the sinking pressure before your very eyes?

I know you mentioned this before, but i'm probably missing your point here. I mean yes, less psi more contact patch area, but i fail to grasp how it's related to the tyre wall/air discussion.
But given you mention contact patch area/pressure, and i hope this won't be too off topic, i wonder how linear a relationship that is? Because I guess your larger contact patch would also mean rubber is not pressed as hard into the asphalt, thus at a more granular level, the effective contact patch doesn't change as much as the geometrical top view perimeter shape would have you believe?
Basically the rubber doesn't 'wrap around' the smaller asphalt features as much.

[segedunum]

I'm most intrigued by this subject as well and hope this thread continues. It's been ages since I've ever considered anything like this and my thinking is well out of whack.

I can take JT's point of view that because the pressure is evenly distributed that it's the carcass that does the load bearing, but I'm not convinced it's as simple as that because you have to take the tyre as a whole - the carcass and the air under pressure inside. However, is pressure even when you inflate non-uniform shapes? That's one thing I've been thinking.

The whole 'load transfer' thing isn't very interesting to me because load transfer happens all the time. If you put a book on the floor and stand on top of it then the floor will end up taking that load, but the book transfers it. Likewise with air in a tyre, because compression from load changes and forces will increase pressure force and place that force on the carcass. In addition to that, we have to consider why we inflate tyres - a last line of absorbtion. Can gas in a tyre compress further up to a certain point without an increase in pressure and transferring the load to the carcass? I'm assuming that's why gas is in a tyre?

I'm just thinking back to JT's straight assertion that air cannot carry load (not the rim stuff that came later). If so, how do we explain lift and ground effect?

I'm simply assuming there is a reason why we don't all use solid tyres and we might be best served looking at why that is.