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Thread: Testing: strut tower movement

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    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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  3. #2
    Still Plays With Cars Loren's Avatar
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    Nice test setup. Before calling it gospel, I'd at least make sure that the results are repeatable. Might be worth fabbing up something to more rigidly mount your dial indicator rig to either the firewall or to the other strut tower. Resting on the engine could be introducing other movements.

    Quote Originally Posted by Daox View Post
    This begs the question, how much more load will the strut towers see in actual cornering?
    If what you're seeing is actual strut tower deflection... from just jacking up one side. It's going to be a lot more. There's no cornering G-force involved in your test, and you're not hitting any bumps. I'd expect at least 2-3x as much movement either from significant G-force, or from simply hitting a sharp bump in the road.

    But, you can't say for sure how much of what you detected was the enging moving around in its mounts. And we all know that the engine can move around in its mounts A LOT on these cars.

    Kudos on taking some action, though! I think it's a good first-round test that points to the need for more testing. (if it showed no movement, or nearly no movement, then there wouldn't be much need for more/better testing)

    Or... if you're just trying to make a product to sell... just make a good brace and people will buy it, regardless! People are funny that way. Make it pretty, put some stickers on it, tell them that it makes the chassis stiffer, improves handling and ride quality, and makes toast in the morning, they'll buy it.
    Simplify and add lightness.

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    Quote Originally Posted by Loren View Post
    Nice test setup. Before calling it gospel, I'd at least make sure that the results are repeatable. Might be worth fabbing up something to more rigidly mount your dial indicator rig to either the firewall or to the other strut tower. Resting on the engine could be introducing other movements.
    I agree that further testing would be good. I'm not sure how I would do this unfortunately.



    If what you're seeing is actual strut tower deflection... from just jacking up one side. It's going to be a lot more. There's no cornering G-force involved in your test, and you're not hitting any bumps. I'd expect at least 2-3x as much movement either from significant G-force, or from simply hitting a sharp bump in the road.
    Thats what I was thinking, but wasn't fully sure.


    But, you can't say for sure how much of what you detected was the enging moving around in its mounts. And we all know that the engine can move around in its mounts A LOT on these cars.
    I think that kind of adds to test. If the engine does in fact move much, it would have moved away from the strut tower in this test.


    Kudos on taking some action, though! I think it's a good first-round test that points to the need for more testing. (if it showed no movement, or nearly no movement, then there wouldn't be much need for more/better testing)
    Thanks. I'm open to suggestions on how to improve the testing.

    Or... if you're just trying to make a product to sell... just make a good brace and people will buy it, regardless! People are funny that way. Make it pretty, put some stickers on it, tell them that it makes the chassis stiffer, improves handling and ride quality, and makes toast in the morning, they'll buy it.
    While this is quite doable, I'd really rather know I'm not producing something thats really just a placebo.
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    Still Plays With Cars Loren's Avatar
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    Quote Originally Posted by Daox View Post
    While this is quite doable, I'd really rather know I'm not producing something thats really just a placebo.
    And that's what I like about you.

    Maybe some kind of strong magnetic base to stick to the firewall would be a good basis for a test rig? Looks like there's a nice flat plane just behind the engine where the VIN is stamped. Or... you could pull out some push-pins that hold the cowl trim in place and bolt some kind of a bracket there to measure from.

    I'm just impressed that you came up with a way to do this in a static condition. I was thinking of testing while driving, which would be much more difficult to do.

    Oh, and you can set up a video camera to watch your test, so that you don't have to try to watch the gauge while you're jacking. You could even jack it up and then bounce the car. Capture it all on video and review it later.
    Simplify and add lightness.

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    I've seen strut tower braces for lots of vehicles and they seem to be the same. One tower is tied to the other. I assume this shares the load between the two towers? But aren't they still moving, or is the bar also tied to the chassis?
    Will weld for beer.

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    Still Plays With Cars Loren's Avatar
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    They can still "parallelogram" even with a good strut tower brace at the top. But, you're basically doubling the resistance to any horizontal movement, so it would have be a really weak system for it to flex much after you put the brace on.

    Without the brace, typical movement is the towers move towards each other as the suspension loads. The brace prevents that. If you hit a bump with one side (or you are cornering hard), the side that wants to tip inward is resisted by the other side. If you happen to hit a bump with both sides, then both side are going to want to tip inward, and they can't.

    The ultimate strut tower brace IS one that triangulates back to the firewall, though. You won't find a lot of them because most people like mods that are quick and easy bolt-ons. To attach to the firewally, at a minimum you'd need to drill some holes into the firewall.

    There used to be a really cool looking Miata shock tower brace that bolted to the firewall. But, most of them don't. Oh, here's the one I was thinking of. Tieing back to the firewall like that, it not only restricts movement inward, but also fore and aft. Tasty stuff. Hard to fit something like that with the limited space under the hood of a Mirage, though. But, Daox is a creative guy...
    Simplify and add lightness.

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    You have the rear sway bar in?? That may factor into lower readings, maybe?
    2018 mirage ES manual

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    Still Plays With Cars Loren's Avatar
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    Rear swaybar transfers more weight to the front. Should be loading the front more in real-world situations.

    For his test... probably didn't make any difference at all because he was jacking a front wheel.
    Simplify and add lightness.

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    Administrator Daox's Avatar
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    So, I found out something interesting about the 2018 Mirage that Failsatheals brought to the midwest Mirage meet this weekend. Mitsubishi added a reinforcing plate to the top of the 2018 strut tower... Here is a picture of his car.

    The type of plate leads me to believe that the steel on the top of the tower is actually thinner than they would like.

    I didn't look to see if anything was added under it.

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    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


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    2017 also

    Quote Originally Posted by Daox View Post
    So, I found out something interesting about the 2018 Mirage that Failsatheals brought to the midwest Mirage meet this weekend. Mitsubishi added a reinforcing plate to the top of the 2018 strut tower... Here is a picture of his car.

    The type of plate leads me to believe that the steel on the top of the tower is actually thinner than they would like.

    I didn't look to see if anything was added under it.
    After reading this post, I went outside and compared my 2017 Mirage. The 2017 Mirage has the round plate on top, too. If there's a good reason for it, the round plate could be easily added to a 2014-15. If something was also added to the underside, that would be more of a challenge.



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