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  #1  
Old 31st December 2009, 04:57 PM
Enoch Enoch is offline
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Question Rear lower wishbone design

Hi folks, I have just about finished cutting the parts to make the wishbones but am not happy with the diagonal braces on the rear lower. My issue is that as it is cut at such a sharp angle, when it is filed to fit the part where it is welded is very thin. I was considering replacing the diagonal with either 1 or two braces that go straight across between the two 2 "arms". I can't see any reason why this would not work, I think they would be easier to weld as they would not be close to the suspension bush tubes, as they are in the original design. Anybody got any thoughts on the matter?
Enoch.
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Old 31st December 2009, 05:47 PM
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Talonmotorsport Talonmotorsport is offline
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If you have enough tube just make the bottom arms a square shape, it will save you hours of head ache in the long run. You will have to bend/force them back to the right size after welding any way as they pull with the book design. Martin Keenan uses the square design on his other cars and I'm not sure why he went down the diagonal design head ache route with the roadster? The only thing is to make the 'fish mouths' exactly right.
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Old 31st December 2009, 05:47 PM
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The purpose of the diagonal brace is to triangulate the wishbone making it strong yet light. If you replace it with two parallel sections you will make the wishbone into a trapezoid which is not as rigid as a triangle. Your idea will end up heavier but weaker.

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Old 31st December 2009, 05:51 PM
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Have you tryed to bend the book design lower rear wishbones? You can move them with your hands, and yes I make mine from 25x2mm cds tubing. The trapezium ones I made for the mx5 rear are solid.
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Old 31st December 2009, 06:50 PM
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No I haven't tried to bend them as I haven't made them yet. I'd expect you can bend them a bit when they're loose but once they're bolted to the chassis which then forms the third leg of the triangle they've got to be strong. If they aren't strong when fitted then as the rear wheels drive the car forward the wishbones would distort and allow the rear suspension geometry to move which would make for some interesting handling attributes.

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Old 1st January 2010, 01:22 PM
Enoch Enoch is offline
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Thanks for your input guys. I still kind of like the idea of 2 parallel braces, it just seems right to me. I might make both and see which one gives the stiffest structure. Weight difference would only be a few grammes so I'm not so worried about that.
All the best,
Enoch
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