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tire vibration modes


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#1 DOHC

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Posted 22 June 2004 - 19:18

In Sunday's US GP, still pictures show that the Bridgestone left rear tire walls have clearly visible vibration modes in the flat out Turn 13 (Turn 1 in Indy 500 terminology). My question is: is this strongly pronounced vibration normal? (One cannot see any such vibration in medium-fast corners, and the Michelins seem much less affected in T13.)

Reference images:
From Atlas Photo Gallery, Sunday race: Look at the picture of Schumacher alone in T13
Saturday practice: look at the picture of Pantano in the Jordan, same spot, same angle.

In both cases, if you look carefully (use 3x image) at the left rear tire's outer tire wall, you see how the tire wall flexes under the load.

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#2 Fat Boy

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Posted 23 June 2004 - 15:42

I see what you're talking about in the picture of the LR tire on Ruben's Ferrari in the speedway turn. I'm not sure how they construct these tires in particular, but I do know that Bridgestone road tires are made in a 9 segment mold and the tire noise has a lot of content on the 9th harmonic. It looks as if something of that nature is happening.

I looked at many Michelin runners, but didn't see anything unusual. If you squint, you might see something on the LF of Montoya's car, but that's really hard to say. There is a lot of tire deflection in all the cars, but that's a different story than a standing wave in the sidwall.

Interesting thing to notice, DOHC....good on ya.

#3 DOHC

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Posted 24 June 2004 - 22:12

Ross Stonefeld (thanks!) has made two cropped pictures of Schumacher's and Pantano's cars. You can clearly see the standing wave on the tire wall.

Ferrari

Jordan

#4 desmo

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Posted 25 June 2004 - 04:26

Peter Wright states in his book F1 Technology that "A tire has more than 50 modes."
Has anyone ever made a tire model that incorporates all of them? It's literally beyond my comprehension. Neat pics though :D

#5 DOHC

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Posted 25 June 2004 - 10:34

The "more than 50 modes" might need some clarification.

The "body" of the tire bends and flexes in accordance with a partial differential equation that governs the (primarily) elastic deformations of the body. Partial differential equations generally give rise to an infinite number of modes. Perhaps Wright means that the first 50 modes are of significance when modelling a tire. But basically, if you use a partial differential equation model for a tire, you will have an enormous number of modes represented. If you solve the equations using let's say the finite element method, the number of represented modes depends on how dense the mesh is. A few thousand modes would be perfectly normal.

#6 Greg Locock

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Posted 25 June 2004 - 11:24

Nicely put. Any continuous system has an infinite number of modes.

The rule of thumb when using modal stiffness to represent a structure is that each degree of freedom needs a mode, so for a tyre we'd want at least 6 modes. Realistically we'd use 200 modes for a spindle, say, so for a tyre 50 seems reasonable.

HOWEVER in my opinion-

those pictures are probably not resonant modes. They show regular wrinkles in the sidewall of the tire, directly akin to that seen in a drag racer's tire at the start of a run.

The tire sidewall buckles into a shape around the the tensile path for the torque.

#7 DOHC

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Posted 25 June 2004 - 19:52

Originally posted by Greg Locock
those pictures are probably not resonant modes. They show regular wrinkles in the sidewall of the tire, directly akin to that seen in a drag racer's tire at the start of a run.

The tire sidewall buckles into a shape around the the tensile path for the torque.


Interesting!

But as you cannot see these modes in "low speed" turns, it appears that under greater loads induced by higher speed, and therefore reducing the time available for the deformation to damp out (it has to damp ouot in one revolution of the tire) is indeed a resonant mode. Even if a mode is resonant it can be damped in the way we see in those pictures. What seems clear is that the deformation pattern is very regular, like a standing (but damped) wave on the tire wall. Modes of that type are usually eigenmodes.

As I'm no tire expert this is mereley a (hopefully qualified) guess, but the pattern really looks very much like an eigenmode. I have never seen that before in F1 tires.

#8 Greg Locock

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Posted 25 June 2004 - 22:49

In the Jordan pic the deflections are very much contained around the contact patch, whereas modal behaviour would be axisymmetric. I'll chase up SAE papers on Monday and see if there's any public domain stuff on the modal properties of tires.

The deflections in the Ferrari pic look more evenly distributed around the circumference,so I agree they might be modal.

To be honest it is a slightly arbitrary distinction, which I didn't quite say above, the static stiffness of a system can be obtained by summing the total modal response.

#9 Scoots

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Posted 26 June 2004 - 14:23

Originally posted by Greg Locock
The tire sidewall buckles into a shape around the the tensile path for the torque.


But wouldn't they be on the forward part of the tire if that was the case?

#10 Greg Locock

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Posted 27 June 2004 - 00:09

http://www.hotrod.co...image_small.jpg

Shows just that. Interesting, I had remembered the distortion as being distributed right around the tyre.

#11 DOHC

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Posted 06 July 2004 - 08:46

In the drag racing case, you have the "wrinkles" forward of the contact patch because the tire transmits an enormous torque.

In the speedway turn, however, the deflections are not due to torque, but to the lateral forces sustained by the tire. Thetire encounters that lateral force at the contact patch, gets deformed there, which excites an oscillatory mode whoch takes a while to damp out. Because the speed is so high, the damping time ("time constant," "half-time" or whatever other suggestive term you prefer) is long enough in relation to one revolution of the tire to make the mode visible. In low speed, that same damping time is short compared to one turn of the wheel, so tire deformation would appear to be local at the contact patch.

My guess.

#12 DOHC

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Posted 19 June 2005 - 20:56

Time to bring this thread back, it seems. Unfortunately the pictures from last year's tire vibrations at Indy's T13 are gone, but maybe they can be dug up somewhere?

#13 soubriquet

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Posted 20 June 2005 - 02:32

Originally posted by DOHC
Perhaps Wright means that the first 50 modes are of significance when modelling a tire. But basically, if you use a partial differential equation model for a tire, you will have an enormous number of modes represented. If you solve the equations using let's say the finite element method, the number of represented modes depends on how dense the mesh is. A few thousand modes would be perfectly normal.


How many modes actually carry information? Do you use an MNF transform to determine and reduce the data dimensionality?

#14 DOHC

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Posted 22 June 2005 - 12:49

Originally posted by soubriquet


How many modes actually carry information? Do you use an MNF transform to determine and reduce the data dimensionality?


I think you need as many modes as necessary to accurately describe the deformation. I would roughly guess that you don't need as many as 50 modes to do that. The data dimensionality is basically only a function of the mesh density, but you need a dense mesh to describe the deformation. That is not the same as saying that one needs many modes. A modal reduction should be possible.

#15 gbaker

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Posted 23 June 2005 - 22:16

Originally posted by Greg Locock
...HOWEVER in my opinion-

Those pictures are probably not resonant modes. They show regular wrinkles in the sidewall of the tire, directly akin to that seen in a drag racer's tire at the start of a run.

The tire sidewall buckles into a shape around the the tensile path for the torque.


I believe Greg has summed it up well, i.e. most, if not all, of the images produced here deal with strain, not multi-modal harmonics.

Torsional strain is a product of, among other things, multi-modal torsional resonant harmonics. I suspect that every F1 team has a gearhead whose job it is to map such things.

Forget the pictures. Pictures are for Salesmen/Gurlymen.

#16 olschak

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Posted 24 June 2005 - 11:45

Hello everbody,
here are three points I want to add to the discussion.
First it is very hard to come with whatever sort of knowledge about physics and arrive at some real-life answers. The opposite, F1 incidents tell you a lot about physics is more true.
Second, we shall never forget that the cars do not roll through a turn, they use the rear tyres to transfer massive engine power. That is the tyre is spinned by the rim from the inside and needs to translate to the outside where there is actually only a contact patch on the tarmac.
Third, the tyre in a F1 car is also 50percent of the suspension by means of air pressure .

#17 Christiaan

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Posted 13 July 2005 - 21:00

Sorry guys, dumb question but what do you mean when you say Tyre Mode???

#18 Greg Locock

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Posted 15 July 2005 - 21:22

I mean a flexural resonant mode of the tire, ie a natural frequency. Head on over to the ftire website for a vaguely relevant useage and description of tire modes. In the real world we are interested in the first 10 or 15, roughly, but there are an infinite number of them.

#19 Christiaan

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Posted 18 July 2005 - 15:18

thanks,

Ross, I couldn't see ur pics

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#20 GeorgeTheCar

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Posted 23 July 2005 - 18:11

Pardon my ignorance but where, which URL, is the tire site?

#21 Greg Locock

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Posted 24 July 2005 - 08:04

www.ftire.com

#22 MattPete

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Posted 04 August 2005 - 14:18

Originally posted by DOHC
Ross Stonefeld (thanks!) has made two cropped pictures of Schumacher's and Pantano's cars. You can clearly see the standing wave on the tire wall.

Ferrari

Jordan


Those links don't work. Could someone post the pics again?

#23 DOHC

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Posted 07 August 2005 - 09:05

I posted those pictures again in the Dumb tyre question thread, see post #16 there.

#24 Ross Stonefeld

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Posted 07 August 2005 - 09:34

Sorry about that, was cleaning my server over the winter and couldnt remember why I had those photos so binned them :blush: