tyre stiffness

[A]

hi guys,
we r using hoosier 20*6*13 tyre in our car...what can be the approximate stiff ness value for it..???from the data on site we have estimated it to be around 100N/mm...we have around 55 kg of wt at each corner..thank you

[wil oberlies]

I assume you are referring to the complex stiffness, which could be modeled by a theoretically pure spring and a pure viscous damper. This would give a response function having a magnitude (the spring rate) and a phase angle (the damping). Be sure to include the wheel stiffness too. I'd say an off the cuff stiffness value would be 7pi.

[Claude Rouelle]

A,

Tire vertical stiffness is (for a given tire) vertical load, pressure, camber,rim size, speed and even wear sensitive. It is also slip angle (lateral force) and slip ratio (longitudinal force) sensitive.

But there is no need to be that complicated as I assume you will use the tire stiffness as aprt of your suspension stiffness and damping calculation.

You can find the answer in your TTC data.

Claude

[ZAMR]

Your car seems awfully light for the question you are asking...

Also there is no 20*6*13 tire. I assume you mean 20.5*6*13, in which case:

https://www.hoosiertire.com/rrtire.htm

If you have no TTC data

-Zach

[STRETCH]

Not forgetting bulk temperature Claude...

[A]

ya..you are right claude..we r using it for apring stiffness calculations..but we dont have TTC data what do we do now???...
Originally posted by Claude Rouelle:
A,

Tire vertical stiffness is (for a given tire) vertical load, pressure, camber,rim size, speed and even wear sensitive. It is also slip angle (lateral force) and slip ratio (longitudinal force) sensitive.

But there is no need to be that complicated as I assume you will use the tire stiffness as aprt of your suspension stiffness and damping calculation.

You can find the answer in your TTC data.

Claude

[Claude Rouelle]

A,

What do you do know?

The answer is simple: you acquire the TTC data!

It is a bit as if a mechanic was telling you that he wants to repair a car but he has no tools: without understanding your tire it will be difficult to go though the design process of your suspension.

Claude

[A]

ya ..u r right ..but we cant afford to spend money on that...ok..but thanx for ur reply
Originally posted by Claude Rouelle:
A,

What do you do know?

The answer is simple: you acquire the TTC data!

It is a bit as if a mechanic was telling you that he wants to repair a car but he has no tools: without understanding your tire it will be difficult to go though the design process of your suspension.

Claude

[Dunk Mckay]

Originally posted by A:
ya ..u r right ..but we cant afford to spend money on that...ok..but thanx for ur reply

What you mean to say is that your design priorities and budget do not allow you to allocate resources for TTC data. There is rarely such a thing as "can't afford".

[Claude Rouelle]

A,

If you can't afford TTC data, don't even try to build a FS car...

If you want to ply in the big guys playground you have to stop wearing shorts.

Believe me the money IS there.

"They did not know it was impossible; so they did it" (Mark Twain)

Stop whining and start winning.

Claude

[exFSAE]

Here's a better question - why do you need it? Why is it critical? Can you not do your initial design work sufficiently well with just wheel rates?

[DougMilliken]

Originally posted by Claude Rouelle:
...
"They did not know it was impossible; so they did it" (Mark Twain)
...
For a smaller team considering TTC data and the analysis required to make good use of it, this quote may also be appropriate?
"They don't realize that we are bringing them the plague." (Sigmund Freud)
The occasion was his visit to USA, and what he was bringing (according to one of my profs) was the very time consuming "talking cure" (psychoanalysis).

[ZAMR]

Originally posted by A:
hi guys,
we r using hoosier 20*6*13 tyre in our car...what can be the approximate stiff ness value for it..???from the data on site we have estimated it to be around 100N/mm...we have around 55 kg of wt at each corner..thank you

Okay I'm confused. If you don't want/have TTC data then what's wrong with the vertical spring constant data from HOOSIER'S WEBSITE.

[Claude Rouelle]

ZAMR,

OK you do not have / cannot afford TTC data.... Really what is your budget to build and race a car As far as budget and being realistic please refer on my post on May 30 at 12:22 PM http://fsae.com/eve/forums/a/t...8/m/48310896441/p/11 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/48310896441/p/11)

But still let's say you can afford TTC data and you are looking for tire stiffness.

What about building a simple plate with a scale activated by hydraulic jack and measure the tire compression with a micrometer? You can do that with different load, camber, pressure etc... Of course it would not be a rolling tire as in TTC test but it would be a good start.

Can you do that?

Claude

[Zac]

Another option would be to make an educated guess. F3 cars use a similar size tire and there are F3 tire models available in most commercial vehicle sims. It stands to reason that the F3 tire will behave similarly enough to the 13" tires run many FSAE teams to get you in the ballpark.

If I were on a first year team and had nothing else to go off of, I'd just grab one of those tire models for my kinematic analysis and be done with it. After building the car you can use testing to see whether or not that was a good assumption. Design judges are more likely to approve of that methodology than just blindly applying the FSAE TTC data anyway.

For a first year team I think the real goal should be to just worry about building a functional car. Once you have some manufacturing processes figured out (and better understand your load cases) then it is time to start going a little more in depth with the analysis.

[Marvel]

Originally posted by Claude Rouelle:

If you can't afford TTC data, don't even try to build a FS car... .....

Claude
Here is what Steve Fox suggested http://fsae.com/eve/forums/a/t...8/m/48310896441/p/14 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/48310896441/p/14) his post of June 18, 2012 12:45 AM..
"Cost less than $2,000 USD to build".... within the ability, materials resources, and budget........
I guess $2000, does not and cannot include TTC data.

Initially, while in design phase (since our team captain was not in favor of getting TTC data) I used to regret "I wish I had it!!"
But when we actually went into production, I realized that we could not have made better use of it.

TTC data is must and is a wide learning resource but to make a basic car I guess you don't need it.