F1technical.net

Jersey Tom wrote:

mep wrote:

for vertical stiffness you can assume between 20 and 30 mm of deflection (at the hub) when 6 kN of force is applied. relationship is roughly linear.

Way to much for just 6kN.
Where do you have those figures from?

Sounds reasonable to me, both the spring-rate and inflation (18-22psi).

Common sense should tell you that the tyre can’t deflect 20-30mm when you apply 6KN (~600kg) on them. The car would simply bottom out during high aero loads and springs will add additional deflection to that.

The inflation should be correct. I said its 1,4bar which is 20,3psi. So its in the range of those 18-22psi. Now comes the calculation of xpensive:

Very simplified, but a start;
- A vertical load of 6 kN and a pressure of 130 kPa (19 psi), would indicate a contact-patch of 45 000 mm^2.
- An area of 45 000 and a contact-patch width of 300 mm, means a patch-length of 150 mm.
- A patch-length of 150 and a tyre-radius of 330, suggests a geometrical deflection of about 9 mm.
- Remaining deflection from tyre-wall.

Does this come across as at all reasonable?

On first view this doesn’t sound reasonable but I said in previous post that the side walls of the tyres are relatively hard. So the closest explanation after this calculation is that the cars mainly run on the side walls because the pure pressure is not capable of holding the car up.

I guarantee you 20-30mm for 6kN load is perfectly reasonable and probably fairly accurate, at that inflation and at a constant speed.

Bear in mind that as speed goes up the tires will grow a little as well.

Also not sure what you mean by saying F1 sidewalls are hard. Don't think I'd agree with that... they are super light weight.

The reason I´m asking is because I´m trying to build more accurate tyres in rfactor for an F1 mod.

In terms of stiffness I can set basestiffness and stiffness per Kpa in pressure.

Atm with the pressures we are using of 130kpa the total stiffness is 270000N/meter. This is a default value from a standard F1 Mod.

Gotcha. 270000 N/m probably isn't too far off. Again since it's dependent on speed, camber, etc.. that's probably decent for a ballpark.

Unfortunately, the tire model in rFactor is pretty awful. I'm looking forward to the Williams F1 car comes out in iRacing..

I guess 270 N/mm is about right, if you have 6000N/30mm on the way there, it's probably far from a linear relation.

xpensive wrote:I guess 270 N/mm is about right, if you have 6000N/30mm on the way there, it's probably far from a linear relation.

Correct

While I can't comment on the stiffnes values, I can say that from the tyre data I've seen, the stiffness is not constant at all. Its very load dependent.

The pacejka tyre model uses 3 parameters to model the deflection, so its not a simple disp=force x stiffness

Tim

Jersey Tom wrote: Sounds reasonable to me, both the spring-rate and inflation (18-22psi).

A summary of front/rear vertical F1 tyre stiffness can be found here.
JT's pressure range is sensible.
Tyres have a "rising rate" stiffness characteristic.
Tyre stiffness varies non-linearly with pressure, but at normal pressures can be expected to increase with increasing pressure by around 8 N/mm/psi.
F1 tyre stiffness usually increases with decreasing pressure at low pressures & low vertical loads.

This is the difference of the 2009 and 2010 front tyre profile:




I expect the stiffness to increase by 50-100% just by looking at the shape.



So the front tyre stiffness could go to 450 or 600 N/mm this year.

I believe you have a bit of xplanation to do with that graph of yours, WB.

It is not mine. It was officially supplied by Bridgestone. If you look at the 2009 sidewall it is instantly clear why this is much weaker than the 2010. The 2010 actually never deviates from the vertical axis to the outside. It only curves to the inside at the top. Additionally the narrower tread will also impact on the over all stiffness of the tyre. The reduced diameter will also support the stiffness of the side wall.

WhiteBlue wrote:I expect the stiffness to increase by 50-100% just by looking at the shape...So the front tyre stiffness could go to 450 or 600 N/mm this year.

I hope not... But I would like to understand the reason for your conclusion.

DaveW wrote:

WhiteBlue wrote:I expect the stiffness to increase by 50-100% just by looking at the shape...So the front tyre stiffness could go to 450 or 600 N/mm this year.

I hope not... But I would like to understand the reason for your conclusion.

Just look back two posts where I have explained my reasoning. Of course the figures are very speculative. I also assumed that the construction in terms of the structural design and the thickness of the fiber layers are similar. 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.

BTW, I have changed the picture source to use a higher res pic.

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?

Jersey Tom wrote:Gotcha. 270000 N/m probably isn't too far off. Again since it's dependent on speed, camber, etc.. that's probably decent for a ballpark.

Unfortunately, the tire model in rFactor is pretty awful. I'm looking forward to the Williams F1 car comes out in iRacing..

xpensive wrote: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.