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Making a strut tower bar: Design opinions/help


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"You just don't get it do you. You need to stop being so hardcore, pull the stick outa your butt and lighten up cat."

 

Gee, mom always said find something nice to say, so I did. That bar has more downforce than any I've seen lately... Ouch, I did it again. Bad keyboard, bad!

 

But seriously, from a structural engineering standpoint you have an extremely challenging situation. If you eventually lower the engine as planned that will do many good things, including providing the opportunity to make a strut bar with some real handling benefit. Meanwhile, you made something that looks cool, practiced nice workmanship, and, snicker... added some downforce. That was "lightened up".

 

And it's kat with a "k". :)

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The issue is that the loads on the bar will tend to bend it, like pulling on a bow string bending the bow's frame. This means that even a very strong bar with such a shape would flex considerably - so much so, that one might question whether such a bar is really effective in helping chassis rigidity.

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The benefit with making your brace into an X shape is that if it tries to bend it will push on the front of the unibody rather than just bending. it would triangulate the whole front end...triangles are good. :-)

Attached pic (japanese Z car) shows some triangualation of the front end. I imagine it is VERY rigid.

s30_019_thumb.jpg

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The benefit with making your brace into an X shape is that if it tries to bend it will push on the front of the unibody rather than just bending. it would triangulate the whole front end...triangles are good. :-)

Attached pic (japanese Z car) shows some triangualation of the front end. I imagine it is VERY rigid.

Thanks for bringing up that pic again OTM. I've seen it before, but never really looked that closely...

 

Anyone else looking at this wondering why they didn't run the tubes all the way to the strut tower? The diagonal bars look like they go through the firewall to a meet at a dash bar maybe. They could go all the way out to the strut towers but stop about 12" short of the towers. Why??? Same with the lower bars that "should" go to the strut towers from what looks like a knee bar. They could meet up right at the tower, but for some reason they hit the bars that come from the dash bar about 6" short. That don't make no sense to me.

 

I do like the sheet reinforcement to the bars that hook in around the swaybar mounts. Might have to do that to mine. You know, while I'm at it... :wink:

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A lot of work went into that. I can see where it would help a lot, but I quess my question is about the fore and aft reinforcement. It appears a great deal of this work was done to prevent the top of the towers from moving fore and aft, and less on lateral movement. My impression of a Z unibody that this is opposite to what is needed for front suspension reinforcement. I would like to understand this better because this is not the first time I've seen this emphasized. I am not picking this set-up apart, only trying to understand and learn from it.

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From the extremly simple FEI analysis I saw done on the 240Z front strut towers, they tend to twist and bend towards the rear about the same amount that they move laterally. This makes some sense if you look at the chassis structure in front and behind the strut towers. The structure is significantly stronger behind the towers then in front.

 

Also, the don't move in parallel laterally (as if in a big parallelogram) but more in towards each other. The lateral brace is important to keep the tops separated by a consistent distance.

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