Utah S2K

I would think you would be fighting torsion flexture of the chassis. I know is pretty stiff already. As stated on this thread...to keep the platform stiff and allow the suspension to work is the goal. As such I was thinking about two short cross members attached to the x-Brace, running perpendicular to the car........

cmnsnse

These sketches are highly exaggerated and very basic, but show how the x brace and strut tower bar would help strengthen the chassy.



I think the x brace would be more subject to tensile stress and the tower bar compression. Im sure if you put enough R/D into it you could reduce the mass of the braces and make them much more effective.

Of course the Spoon brace is probably just fine for 95% of buyers . . .

dbarnes

Based on the the location of the x-brace, I would say that it is designed to carry the load in the plane of the brace. It appears that the goal is to take the lateral load from the lower front suspension and transfer it to the frame. To do this, the load that is transmitted to the front corners of the brace must be carried as a combination of bending and axial load in the front legs of the brace. The gussets at the vertex help to get the load around the vertex (also increases stiffness and weld area at points of high stress) because one leg will be in tension while the other is in compression (this is the way a thin sheet carries an inplane shear load - diagonal tension). So to answer the question posed by Mingster, I think the cross section of the brace is oriented correctly with the strong axis of the cross section being perpendicular to the brace.

Now if you wanted to stiffen the brace, the best approach would be to add four additional members that connect the four corners of the brace. By doing this there are now no unsupported loads (i.e., "kick" loads) coming from the front suspension, and thus the load can be reacted as axial tension and compression in all legs of the brace. This would most likely result in a very stiff brace because axial load path is much more efficient than bending load path.

Sorry for the long post.

-Donnie

cmnsnse

Very good explination, but I dont fully agree about what stresses are presented:

I dont think the x brace is being skewed, resulting in tension and compression, but rather just tension (for the most part)
I think the brace is more likely stressed from opposit corners. The main chassy and cross beams already there resist skewed stress and that would be the presentation of a frontal collision of only one side.

I feel that any reinforcing of the right an left sides (corner to corner) would be negligable because of the frame work already there. And that for and aft bars just are not needed.

dbarnes

cmnsnse,

I agree with you that the brace is designed primarily to carry axial load. However, because the x-brace is offset from the sub-frame and the load is developed by a lateral acceleration, the load is introduced into the x-brace at some anglular offset from an x-brace leg (could probably figure out the angle if the free-body diagram of the system was drawn). Because of this offet, each leg must carry axial load, bending and torsion. Furthermore, because of the angular misalignment of the load, there will be some "racking" of the x-brace. I do agree with you that most of the lateral load is carried by the sub-frame, but not all of it (sub-frame is not infinitely rigid). All I was saying when I suggested adding four beams connecting the four corners of the brace was that this would eliminate all racking from the brace and allow all load to be carried axially in the various members of the brace.

-Donnie

cmnsnse

I read ya, I only think it would be more trouble than its worth, being with minor results on top of what is already dont by the brace.

This is the only pic I have online(so far), and its not really the main chassy either.

dbarnes

I agree with you - the Spoon x-brace is fine the way it is. I was just trying to answer Mingster's original question.

-Donnie

cmnsnse

I think we both did

lvs2k

Don't you think that the stresses the chassis is subjected to are, as a rule, far less than what the original design tolerances allow for? This makes for a chassis more rigid than a lot of coupes/sedans.

elviscos

Is it possible to measure the flex with and without the xbrace or the forces, if any exhibited on the xbrace?