How flexible do you think a stock, trailing arm is Options

[ChrisFoley]

Specifically I am looking for rotational stiffness (ie. twist) of the trailing arm due to the tire contact patch resisting sideways sliding of the car. I'm only interested in forces greater than 1G during cornering.
I already know what happens but go ahead and take a guess. (IMG:style_emoticons/default/biggrin.gif)
I'll post pictures of my test fixture shortly.

[ChrisFoley]

and here's a pic of the rewelded trailing arm. The metal piece I inserted is about .075" thick.
This had the same effect as adding the boxing kit but it still isn't enough for me. I plan to add one or two more things to get the flex down to 50% from the stock arm.

[Thorshammer]

Chris,

If we move the contact patch outboard we will increase the twisting force becuase we change the fulcrum. I am pretty sure this is correct.

As for the discussion earlier, why we need to know specifics is, when setting up the static geometry and knowing the amount of chassis roll, as well as knowing the degree of deflection of the trailing arm, we can understand completely what is happening, and after the arm is strengthened and the camber and toe curves are known, we can better determine what the static camber and toe should be set at to get the best performance.

Other factors such as Roll center and instant centers will need to be taken into account as well, several people are working on this as well. I think Brett, Chris, Kevin and I are attempting to ensure this has been thoroughly investigated and we have soild data and can prove the methodology. We have to ensure the stiffness of the chassis and components prior to altering other parameters or the feedback from the chassis will not be 100% accurate. We know D Finch alters the trailing arms, and Kevin has a stunning idea that may bear fruit, but we will have to test to make sure. If his season starts this year like last, he will need studded tires and a plow on the front of that thing.

More later....

Erik Madsen

PS: EP is me and Kevins race at 4:00am which is only 1 am for you west coast guys.

[TimT]

Chris thats EXACTLY how I imagined reinforcing the trailing arm. I thought of a way to get reinforcement inside the trailing arm without cutting the arm in half, I may try it on a damaged arm I have laying around.

[ChicagoChris]

Ok.. Which interior surface did you reinforce?

Did you do the reinforcing to the arm you first tested or to a different arm?

[Thorshammer]

This is a piece of metal that is welded between the two halves.

Tim,

Chris and I have discussed two different methods, one is what Chris has done, next we want to try cutting slots at and angle so that the trailing arm can be triangulated by three peices. This should increase the torsional rigidity to what we are looking to do. Then we have another to reduce the lateral bending moment. We will see what is needed.

Erik

[TimT]

My thoughts were to cut slots also, and insert reinforcement and weld it in place. I though of doing it in 2 or 3 places.


Also the distance of the conact patch from the cl of the training are does matter. If you have the wheel spaced out very far, you increase the fulcrum that is acting on the trailing arm. It may not be a significant amount, but I dont think it should be neglected. I am going to try and crunch some numbers later and see what I come up with.

[ChicagoChris]

OK. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

[ChrisFoley]

If we move the contact patch outboard we will increase the twisting force becuase we change the fulcrum. I am pretty sure this is correct.

The amount of wheel spacers you use is largely due to the specific wheels you use. That's why I said it doesn't matter how thick they are. My wheels are offset differently so I don't need much wheel spacer.
However, EP allows you to have wider rear track which does affect the loads. I just don't think the distance is great enough to alter the methodology of what we are doing.

While I gree that cutting slots is the easy way to accomplish this I want to be able to alter the geometry at the same time. What I need next is the best location to add more stiffeners.

[ChrisFoley]

QUOTE (ChicagoChris @ Dec 17 2005, 05:35 PM)

Did you do the reinforcing to the arm you first tested or to a different arm?

same arm as in the first test

[McMark]

Would it be more advantageous to weld a plate non-perpendicular to the centerline of the boxed section? i.e. 45 degrees off in two axis?

[r_towle]

I thought you were busy. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Really looks great...

Have you given any thought to carbon fiber re-inforcement???

Not sure of a good structural way to bond it to steel, but this concept is being field tested on old bridges that need additional structural repairs...just a thougt


Rich

[rick 918-S]

QUOTE (McMark @ Dec 17 2005, 03:26 PM)

Would it be more advantageous to weld a plate non-perpendicular to the centerline of the boxed section? i.e. 45 degrees off in two axis?

I was thinking the same thing Mark. (IMG:http://www.914world.com/bbs2/html/emoticons/unsure.gif)

[Brett W]

OK, you go to all the trouble to fix the flexible trailing arm. That is good. But you don't solve the problem of the moving roll center caused by your toe and alignment changes. This is another reason to build a different trailing arm.

I am on this now and hope to have some data by Monday.

[rick 918-S]

(IMG:http://www.914world.com/bbs2/html/emoticons/popcorn[1].gif)

[Dave_Darling]

Chris, thank you very much for doing this testing, and for sharing the results with us!! It is fascinating reading.

--DD

[Bleyseng]

Yes, its interesting but... I like Muellers idea for tools to measure with instead of that level.


(IMG:http://www.914world.com/bbs2/html/emoticons/popcorn[1].gif)

[Mugs914]

This is one of the best threads I've seen here! Thanks for the effort and for sharing the results Chris! (IMG:http://www.914world.com/bbs2/html/emoticons/pray.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/pray.gif)

Here is the way we reinforce trailing arms. It isn't an original idea and most of you have probably seen it before, but here's a pic just in case. Its a 'tubular" method...

The tube goes from the bearing carrier diagonally through both sides of the arm. Triagulates and stiffens the walls of the arm in one shot.

Never have tested one, maybe we should send one out to you so it can be compared to others on the same rig. It would be nice to know if we are accomplishing anything.... (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

[Mugs914]

Here's a shot that shows where the tube comes through the inboard side.

[Mugs914]

Outboard side...

[McMark]

That arm has an option for increased shock travel? Am I interpreting that correctly?