Kz vs. speed 2

[RoterHelm]

Hi, excuse me my bad English. I would, if possible, give me your opinion on an issue:

I want to model one quarter of vehicle. The tire manufacturer provides Kz (for different pressures and camber angles), but does so for a given speed (125 Kph). I have understood that Kz varies linearly with speed and Kz increases if the speed is increased (effect of centripetal force) but what I can know how much. There any way to make a rough estimate. Knowing the type of tire, size or something else might be able to determine about this variation?

Regards

 

[GregLocock]

By Kz do you mean the vertical tire stiffness, ie you want to know the change in rolling radius for a given load and speed?



Cheers

Greg Locock


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

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

 

[RoterHelm]

Hi, Greg

Yes, that is. The graphics I have are deflection (mm) vs. Load (Kg) for different camber angles and different pressures. Then, I have the vertical stiffness for different camber angles and different pressures, but all these plots are at 125 kph. My intention is to know, for a given pressure and camber, vertical stiffness for different speeds to 125 kph.

Kz varies linearly with speed (something like: Kz=a*V+b, b>0) and Kz increases if the speed is increased (a>0) but what I can know how much ¿? I wonder if there is any way of knowing about what is the slope of that line knowing, for example, the dimensions of the tire or the tire is radial and so on.

Regards, Roter Helm

 

[RoterHelm]

Hi, i've been thinking about this and I have some doubts:

If the graphics are deflecction (m.m) vs. Load (Kg), is not entirely correct to obtain the vertical tire stiffness( Load*9.81/deflecction) of calculating the slope of the line. The force that causes a certain deflection is the weight + the effect of centripetal force, not just weight. What do you think about this?

Regards, Roter Helm

 

[GregLocock]

True, but there so many complexities in what you are trying to do that you are going to be here for the rest of the year thinking of more difficulties.

I don't actually know where to go from here, any test in the real world is going to find it hard to differentiate between vehicle effects and tire effects.



Cheers

Greg Locock


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

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

 

[RoterHelm]

True, you're quite right, Greg. This issue could be enough for a paper. That is not my intention now.

It could to take the stiffness constant. It´s a Formula Ford ("No Downforce"), is not critical the ground clearance.

Thank you

 

[cibachrome]

They can (and have) run such tests routinely at TIRF. A speed sweep is generaly used to determine at what speed the static rates stabilize into dynamic rates. There is also other machinery that can perform such tests and obtain the information you asked about. I suppose I could post a video on Youtube and reference such a test in progress if anyone is interested...

 

[RoterHelm]

Hi, cibachrome.

Sorry, I'm not sure understand you. My English is bad.

I have not the means to conduct such a test.

I love to see this video.

Regards, Roter Helm

 

[cibachrome]

By your command:

http://www.youtube.com/watch?v=S4O7b0-epBo

http://www.youtube.com/watch?v=SgrY-LN4GUs

http://www.youtube.com/watch?v=I2o1rxMGFdI

In God We Trust. All others bring data...