How stiff are F1 tyres?

[mep]

It is not mine. It was officially supplied by Bridgestone.

Bridgestone themselves have said that the tyres would be more rigid to accommodate the higher fuel weight, but I can't find that quote at the moment.

What are you doing to get access to such kind of information?

[WhiteBlue]

It is not mine. It was officially supplied by Bridgestone.

Bridgestone themselves have said that the tyres would be more rigid to accommodate the higher fuel weight, but I can't find that quote at the moment.

What are you doing to get access to such kind of information?

Read published information on the web.

[mep]

So would you be so kind and post us links to your sources?

[WhiteBlue]

DaveW posted the second Pic link http://davew.webs.com/TyreStiffness2.png in viewtopic.php?p=142501#p142501

The profile diagrams can be found at http://www.racecar-engineering.com/imag ... ration.jpg and http://www.auto123.com/ArtImages/113900 ... inline.jpg

[xpensive]

But you still have some work to do in xplaining the two plotted graphs, which led you to a four-decimal relation between front- and rear stiffness?

Where are those values coming from and what are those graphs supposed to prove anyway?

The front stiffness 2009 will have been the maximum from the plotted points in the diagram because the grooves are gone. So I'm assuming 350 N/mm. If you apply the factor of 1.5 - 2.0 that I have guessed you end up with the quoted values.

But you haven't proved anything, just shown a graph of some plotted values, without references or xplanation,
and some additional guesswork?

[WhiteBlue]

But you still have some work to do in xplaining the two plotted graphs, which led you to a four-decimal relation between front- and rear stiffness?

Where are those values coming from and what are those graphs supposed to prove anyway?

The front stiffness 2009 will have been the maximum from the plotted points in the diagram because the grooves are gone. So I'm assuming 350 N/mm. If you apply the factor of 1.5 - 2.0 that I have guessed you end up with the quoted values.

But you haven't proved anything, just shown a graph of some plotted values, without references or xplanation,
and some additional guesswork?

You are invited to do your own guess work. Mine is just an educated guess which I have said from the start. Do you want to involve me in a silly argument like the one we had about the resource restriction head count? I'm happy enough if it turns out that stiffness increased just 20%. Does it really matter? All I'm saying that all things equal the 2010 profil will be much stiffer than the 2009 according to Bridgestone's profile. Do you denie that?

[xpensive]

No reason to continue this as long as you refuse to properly xplain those plots and what they are supposed to prove.

[WhiteBlue]

No reason to continue this as long as you refuse to properly xplain those plots and what they are supposed to prove.

sigh...

So lets do it the hard way! Follow me through a simplified structural analysis of the shape. I'm going to assume the same moment of resistance along the whole profile.

1st step identify the left tyre shoulder point where the tread runs into the side wall and lets assume we have the same load on the tread.

2nd we will simplify things by shifting the whole force from the left side tread to the shoulder point. We are integrating the tyre to track pressure here and are replacing the tread by a momentum that acts at the tyre sidewall in the shoulder point to bend the side wall in clockwise direction. So we have now reduced our problem to just the side wall.

3rd we recognize that the same force acts on the tip of the 2010 and 2009 side wall but the momentum is significantly reduced from 2009 to 2010. This is because the width of the tread is reduced in our integration of the pressure. The effective leverage is reduced. Now we figure out how the decreased momentum will bend the sidewall and how the same force will bend the sidewall with more or less sidewall curve.

4th we see that both load components (force and momentum) lead to less bending of the 2010 sidewall. The effective leverage where the momentum attacks in the 2010 version is shorter on top of the momentum being smaller. The same force will also bend the sidewall less in the 2010 version than in the 2009 version because the deviation from the vertical is less in that sidewall.

5th we see that the vertical deformation of the side wall at identical force will be reduced in the 2010 version. In other words the stiffness is increased.

QED

[DaveW]

But you still have some work to do in xplaining the two plotted graphs, which led you to a four-decimal relation between front- and rear stiffness?

Where are those values coming from and what are those graphs supposed to prove anyway?

X, I generated the plots from rig tests of various F1 vehicles. As I (e)xplained in the legend, each point is the average of between 30 & 100 stiffness estimates extracted during one rig test. The points don't represent a completely consistent set, because I didn't choose the test conditions (pressures, temperatures, camber, vehicle weight, "aero" down force, etc. were all the choice of the various customer teams). Lots of caveats to be made about rig test estimates, of course. I can only state that the estimates shown were obtained using a consistent and highly repeatable procedure.

What is interesting (I think) is way the results fall into two distinct sets and, within each set, the consistency of the rear/front ratio for results spanning several generations of tyre (& tyre manufacturer, for the first set). Apologies for the number of significant figures shown in the slopes of the two Excel-generated trend lines (linear, & forced through 0,0) - that was down to Microsoft & my neglecting to override default settings.

I wasn't trying to "prove" anything, as such, I was simply providing historical information in response to the OP's request. Be interesting to see if simulations can detect performance differences between the two sets (hint: the second set will require a more forward c.g. & aero bias than the first). I would appreciate feedback on that aspect.

WB, You did answer my question, thank you. You posted whilst I was still fumbling with my request. I'm afraid you were incorrect with your assumption about the stiffness of the current front tyre, & I suspect that the assumptions you made to predict a stiffness for the 2010 front tyre may not be entirely accurate either (with apologies), although I'm sure aero specialists would wish it so.

[WhiteBlue]

WB, You did answer my question, thank you. You posted whilst I was still fumbling with my request. I'm afraid you were incorrect with your assumption about the stiffness of the current front tyre, & I suspect that the assumptions you made to predict a stiffness for the 2010 front tyre may not be entirely accurate either (with apologies), although I'm sure aero specialists would wish it so.

Could you elaborate on both points, please. I would appreciate your reasoning. Where do you think the front tyre stiffness was in 2009? You are much better equipped to make a guess there. On the second point I would also like to hear your reasoning.

[Jersey Tom]

Amazing how many threads seem to drag on pointlessly...

[DaveW]

Could you elaborate on both points, please. I would appreciate your reasoning. Where do you think the front tyre stiffness was in 2009? You are much better equipped to make a guess there. On the second point I would also like to hear your reasoning.

There appears to be no consistent difference in stiffness between grooved & non-grooved tyres. In fact, the highest estimate in the second set was from a 2005 rig test. If I were to use the results for a simulation of a 2009 vehicle, I could not do better than a simple average of the individual results shown in the second set of estimates.

A persistent problem in recent years has been achieving the correct working temperature in the front tyres without over-working the rears. My plots suggest indirectly why that was the case. A way of improving that "balance" would be to make the front tyres more compliant (less stiff), relative to the rears. I'm sure that Bridgestone is aware of both the problem and the solution & I am quite sure that their tyre gurus would not wish to compound their 2009 problems by increasing front tyre stiffness (at least, not without doing something fairly major to the rear construction). If it is assumed that no good case can be made for a major change to the rear construction, one might guess that the temperature problem would be alleviated whilst modifying the tyre to satisfy the requested change in dimensions, leaving teams to cope with the aerodynamic consequences. After all, tyre stiffness is as much (if not more) dependent upon what is put inside the profile, as it is on the shape of the profile itself.

[WhiteBlue]

There appears to be no consistent difference in stiffness between grooved & non-grooved tyres. In fact, the highest estimate in the second set was from a 2005 rig test. If I were to use the results for a simulation of a 2009 vehicle, I could not do better than a simple average of the individual results shown in the second set of estimates.

I would then conclude that we were at 300 N/mm in 2009. Not so much difference to 350.

A persistent problem in recent years has been achieving the correct working temperature in the front tyres without over-working the rears. My plots suggest indirectly why that was the case. A way of improving that "balance" would be to make the front tyres more compliant (less stiff), relative to the rears. I'm sure that Bridgestone is aware of both the problem and the solution & I am quite sure that their tyre gurus would not wish to compound their 2009 problems by increasing front tyre stiffness (at least, not without doing something fairly major to the rear construction). If it is assumed that no good case can be made for a major change to the rear construction, one might guess that the temperature problem would be alleviated whilst modifying the tyre to satisfy the requested change in dimensions, leaving teams to cope with the aerodynamic consequences. After all, tyre stiffness is as much (if not more) dependent upon what is put inside the profile, as it is on the shape of the profile itself.

OK, I can see where you are coming from. Your main criticism of my analysis seems to be the "all things being equal" hypothesis. Which basically means due to the perceived need for softer tyres you think the construction will over compensate the effect of the outer shape. That is certainly possible and I cannot argue with that view due to lack of data. For now I stick to my view that based only on outer shape (we actually have nothing more at this time) the front tyres will become stiffer.

[DaveW]

I would then conclude that we were at 300 N/mm in 2009. Not so much difference to 350.

I understand why you said that. However, the difference would be equivalent to an increase in pressure of around 6 psi (0.4 bar). You might like to try that change on a road car (for a short time & on a strictly experimental basis). I imagine the effect would be quite noticeable, even subjectively. Then think (but only think) about the effect of doubling the stiffness....

[Jersey Tom]

This is comical.