AW11 rear tie rod test

 

I wanted to do compressive and tensile testing but since I only had two twosrus rods and three OEM rods I decided it would give me more trustable numbers to do one type of test twice. Looking at the real world failures I have seen and looking at the physics of the components I decided compressive was the most likely mode of failure so I focused my efforts there for now.

I am still looking for more OEM and tworus tie rods to do further testing.  Once our tie rods are available I will give a discount to a number of people who send me their old tie rods.

Being a direct competitor I figure most people would question the legitimacy and honesty of my tests. I can't blame them considering I always question the legitimacy and honesty of any internal test. Unfortunately I cannot afford to pay an independent testing facility to do it. Even if I did that could come under question.
So what I did was document the testing procedure as best I could.
From there you can take it or leave it.

You can however look at my process and check and verify the legitamacy of the technical details I discuss below.

I have proffessionally done very similar testing in an ISO certified company on many projects including military, aerospace and many other fields requiring a very high level of accuracy, repeatability and documentation. My setup isn't the most advanced but this is not my first time making and working with equipement like this.

To start things out let's talk about the theory that started this all out.
I used to stand behind the Twosrus tie rods and defended them any time they were questioned. At that point I trusted Twosrus to properly engineer such a vital component and I also thought they looked pretty damn beefy.
One day not too long ago I was reading through the fine print of their listing for the tie rods and realized it said the hex connecting linkage was made out of 303 Stainless steel.
Standard 303 has about half the yield strength as mild steel.
The hex center section looks much stronger but remember that the threaded part at both ends is the same diameter as the stock tie rods. That means that even if the stock tie rods are just basic mild steel that area should be much stronger than the twosrus version.
Unfortunately having half the yield strength does not correlate to having half the overall strength in X test. That will also come down to the shape of the part, and how it all works together.
So the question is how strong is this component in it's design and in it's application. This test will not entirely answer that question but it will give us some idea. I tried to replicate the position, angles and loads as best I could to those it would see in position on the car. Since it moves this would be just one snapshot of one spot in it's range of movement but it should give us a good idea of how the two compoenents compare.

The stock tie rods have the thin tubing for the center section and then rod that threads into that which is the same diameter of the bolt.
Theory says that this rod would absorb a good bit of energy and bend quite a bit before reaching it's yield point. It would also make sense that the whole rod would bend quite a bit past the point of yield while still being able to do it's job get you home safely.


 

The twosrus tie rods on the other hand have very strong inner and outer joints. Combine this with the much thicker much more rigid hex section of connecting rod theory would say that the arm would be very rigid until the moment when that thin threaded section of 303 started to yield the tiniest bit. At which point it would be expected that this point would fail very quickly and more violently as all the movment is happening in this small area as opposed to over the whole length.

 

So now it was time to put the theory to the test.

Test was a basic compressive test.
I started by putting them under an initial load to take all the play out of any components and to settle everything at a good predictable baseline. The first tick on my gauge was 60 KG/cm2. I would need to find out the size of my ram to find out the actual force applied but this is comparative testing so it doesn't really matter. My gauge also displays in tons but I am not sure if that is metric or US tons. I found it weird that it would display in standard units for force applied and metric units of force/area.
My indicator is metric and I prefer to work in metric plus the tics were closer together so I went with KG/cm2.

 

The first tie rod was a haggared old stock tie rod a buddy sent me. Someone had taken the big tools to it to try to get it to spin again. The tube was already mangled, crushed and looked like it should not hold up very well.


At the initial load of 60 KG I zeroed my dial indicator.

From there I compressed the tie rod .5mm and then measured the pressure.

 

 

I didn't have a fixed formula on how far to test the tie rod. I just went until it reached yield and then a few more steps to give an idea of the down slope after it yielded.

Yield is the point at which the pressure plateaus and then starts to drop. It is at this point that the material has permanent deformation and will never be as strong as it originally was.

I will post all my photos below so you can get a bit of a time laps of the tests on each tie rod. I won't be doing this today because my website and data entery methods suck and it will probably take me a half a day to do it.

The stock tie rods performed about as expected. They took quite a lot of compression and movement before the pressure dropped. They also bent over a very large area leaving the overall integrity pretty decent even after some serious compression and bending. Your car would have some serious toe out but overall would still do it's job fairly well.

This is a stock tie rod after reaching a max of 140 KG/cm2 and being compressed a total of 4.5mm. At which point it's resistive strength was about 110 KG/cm2.

I was actually pretty impressed with how well the tworus units did af far as how much force they took before yield but at the point of yield  they performed exactly as predicted. Once that small threaded section of 303 started to go they bent hard and fast and lost almost all strength. A pretty horribly deformed stock tie rod will still have much of it's original strength. Once the twosrus units have bent a little it's over.

This is the tworus tie rod after reaching a max of 125 KG/cm2 and compressing a max of 2.5mm. At which point it's resistive strength was only about 85 KG/cm2

 

You can see the actual deformation has been much greater and the rod is much weaker. Remember that this rod has only been compressed half as much as the stock rod. In a real world situation where the same force was applied this weaker joint would move much further than the stock one.Due to how small of an area is taking the stress and the metals yield and work hardening properties it is quite likely it would loose all strength or even break off shortly after this.

 

 

I just got done with the first test on our new tie rods.
http://www.matrixgarage.com/products/matrix-garage-reear-tie-rods
I will be doing more testing and add more details and data here but for now this will have to do.

So now for the final results here is the graph of pressure over distance.

 

To my disbelief the mangled tie rod outperformed them all.
Of course the other OEM tie rod had some light crushing of the center section tubing. More importantly the tie rod end was twisted about 20 degrees off of where it should have been to be properly lined up. I tried to spin it back but like most stock tie rods it would not budge so I did the test with it cocked a little bit. This may have sacrificed more strength than the crushing of the others tubing.

 

So there you have it. In this particular test with this partiular and sadly small sample group the strongest twosrus tie rod barely beat the weakest OEM tie rod and still failed much faster and more catastrophically than either of the OEMs.
 

 

Here are some side by side pics of all four.

 

 

And a couple pics of one tie rod someone else sent me who had two of these fail on his race car before going back to stock tie rods. He has never had stock tie rods fail on this or any other car.

 

courtesy of webmatter.de