Tire Deformation outside contact patch

[gelwoody]

Hello,

I have a question regarding tire deformation where I'm hoping someone could shed some insights. I'd like to get some understanding of the nature/magnitude of loaded tire deformation IN THE TREAD REGION (not on the sidewall) and OUTSIDE THE CONTACT PATCH. As I understand it (which may not be correct), tire engineers assume, at least as it applies to various tire engineering equations, that loaded tire deformation in this region (again - latitudinally not on the sidewall and circumferentially outside the contact patch) is zero or negligible. If it is 'negligible', could anyone give me some insights as to how negligible? Is it mm, tenths of mm's, tens of microns, etc?

Thanks for your help!
Graham

 

[GregLocock]

It must be of the order of several mm. Try fitting a constant length belt to the deformed shape of the tire, assuming the belt length is unchanged, for a known contact patch shape. I'd have thought a couple of minutes with a camera would provide the data you need.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[CapriRacer]

First, I think tire engineers only assume the rest of the tire is round for convenience. Otherwise, they are stuck with a much, much more difficult problem. If this assumption causes problems in doing an analysis of something, then they will need to deal with that.

Second, the problem of what happens to the tread outside the footprint is even more complex than just the static deformation. There's a thing called a standing wave that appears on the trailing part of the tread surface - and it grows with speed.

On my web page on Tire Speed Ratings, I have some photos of standing waves:

Link

And magnitude? I think we are talking mm - at worse 10mm.

But why do you ask? Are you trying to closely fit something to the tire in this region?

 

[Tmoose]

Granted the following videos are of tires not just rolling along, but Check out 1:00 here-

https://www.youtube.com/watch?v=E_u0YR10Vo0

or 0:50 here -

https://www.youtube.com/watch?v=lNjJaTt0hNw

or 1:20 here-

https://www.youtube.com/watch?v=mfJejgODr3E

 

[GregLocock]

I wonder if the Ftire model replicates this accurately? The general concept is called enveloping. I do know that a couple of tire suppliers can run fairly detailed non linear FEA models that would correctly model this, but of course they won't release anything into the public domain.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[CapriRacer]

Tmoose,

The first video shows that standing wave quite clearly.

But the second and third videos show the tread buckling as it enters the footprint - something different than what this discussion is about.

 

[cibachrome]

At the risk of comments from the disbelievers, I will reveal how we did such an investigation. We filled the tire with cement (as much as possible before reseating the bead), loaded it to the useage load, pressurized it and let it dry. Then we cut the tire out from the cement and digitized an envelope of the tread area(s). Yes, I know, its the INSIDE of the tire, not the outside, but you should get the process and can apply it to other parts. Then you fit a spline function (Matlab) to the area(s) of interest and compute the circumferential lengths, and curvature. Compared to the unloaded tire, the deformation in the tread area is not uniform (linear).

Looking for sources of rolling resistance and locations. Top of the tire is kinda weird, too.

 

[CapriRacer]

Ciba,

At the risk of derailing this thread:

Did your study determine that the belt causes the tread to bulge out at the ends of the footprint? Did the study determine that the tread "circumference" was essentially the same as the free standing circumference? Was it published somewhere?

BTW, if you want to continue this discussion elsewhere, email me at Barry@BarrysTireTech.com