Testing: strut tower movement
In a recent thread I started, seeing if there is any interest in front strut bars, Loren made a point about testing to see if there is any actual measurable proof the the strut tower moves under cornering. Its a great point and one definitely worth considering before going ahead and designing or fabricating anything. So, I decided to give that testings a shot today.
First, lets take a look at the strut towers. At first glance, they seem to be well constructed and fairly solid. They seem to be tied into the firewall fairly well which ties both towers together. However, upon further inspection, there definitely are some weaknesses that I found.
This is the base of the passenger strut tower. You can see a large gap between the tower and a brace that ties the lower parts of the tower together. This is definitely not the strongest joint. The driver's side is the same way.
Next, lets look at the actual material thickness. The top rim where the strut sticks through seems to be a decent gauge thickness. However, through the stamping and forming process, the material gets thinner in some areas. If you look toward the rear of the tower, you can see that it is actually a decent amount thinner in this exposed area.
Finally, there is a bar that goes across the top tying the two towers together. It seems decent enough, but there is room for improvement. A few quite small spot welds hold things together.
So, lets get on with the test, right? The test setup was simple, and honestly not ideal. I used a dial indicator on a magnetic base to measure movement as I jacked up one side of the car. Sadly, there was no good place to mount the base. I ended up putting it on a 1/4" metal plate on top of the valve cover. The actuation of the indicator shouldn't move the base, but I tried to take that into consideration anyways since the base was not firmly fixed in place, and the engine is not an ideal place to read from to begin with. A much better place would be the firewall, but I was unable to get the base to firmly mount to any part of it.
So, this is the test setup.
After I got that setup, I stuck my floor jack under the car. I jacked up on the control arm as close to the wheel as I could get to simulate cornering or going over bumps.
As I jacked it up, I kept an eye on the dial indicator. The higher I went, the more it moved. As my jack got as high as it would go, the dial indicator peaked out at this reading.
I then lowered the car back down slowly. Once it was back on the ground, I snapped another shot of the dial indicator to see how much it had moved. It definitely had moved, but not too far.
Lets look at the numbers:
Before test: 0"
Max movement: .037"
After test: .006"
I think it is safe to say that jacking up the car alone moved that tower at least .031". Is it safe to say that the other strut tower also moved the same amount? If so, the towers are moving around 1/16". In my opinion this is significant. This begs the question, how much more load will the strut towers see in actual cornering? I am unsure. I would guess it is greater than just jacking up the car though. This means those towers are moving even more than that.
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