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I'm planning on using a Stock crossmember and bolting it to the chassis. I was planning on having the front bolt somewhere along tubes J1 and J2. The front crossmember has the engine, steering rack, swaybar, and front bushing of the control arm mounted to it. I don't think that a 1" square tube f RHS will support all this through two bolts on each side (Standard mounting). What would be the ideal way to handle this? Triangulate the area, use a larger tube for the top rails, or do something else?

Since I wont be mounting the suspension to tubes LA, LB, & FU1-2, is it really necessary to have these? Can I eleminate the FU tubes? Or would it be best to just leave them?

Calculate the loads, for one. Short of that, triangulate the area, but regardless, be SURE to weld in bushings for the bolts!!!

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

I know how to calculate the static load, but how do you calculate how much load it will see during driving? Like if I wanted to calculate for .5G lateral load. Would I just take the weight of the front axle, divide it by two and add this to the load figure? Would the mount see all this load or would it see more or less?

Yes, in a simplified way, but the real problem is/are potholes. How much force does a pothole apply? It depends on a million things. In a nutshell, I gave up and calculated the A-arm values for a 10 G load.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Okay cool, so then how do I turn that into an equation or general rule for the size tubing I would need?

Control arm design is an engineering statics problem. If you give me the 3 points that make up a control arm you want to design, I can help you out. The tubing size totally depends on the angles the tubes are at. Having really long narrow control arm can easily lead to really high stresses and increased compliance.

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Matt Giles
www.gilesprojectcar.blogspot.com

Ah, no no no. I'm using the stock Legacy control arms. So I have no doubt it'll be strong enough. I was wondering about the strength of the chassis tubing.

Using generous figures it'd end up at like 12,000 lbs worth of weight in a worst-case scenario all feeding through tubes J1 or J2. Roughly 1000 lbs for the front axle weight, 10G at a pot hole, 2G while turning. I don't forsee being able to pull 2G's, but just to overengineer. Also, I don't see all this force going through one of those tubes, since the crossemmber will transfer some of the force to other parts. Anyway, I just want some opinions mainly.

it should be fine to use the subframe, just make sure it bolts to the rest of the chassis nice and square like it is supposed to. thats basically how a fiero got it's engine front engine on a subframe with suspension repackaged in the rear. thats basically all it is.