locating/reinforcing weak points in a chassis

bryson · Post by **bryson** » Mon Apr 09, 2007 5:17 pm

Well it's not for my Fiero, but I'm trying to determine some methods used to determine weak points in a chassis. We can keep this pretty general, but the car in question is my AE86. I've cleaned up the engine bay a lot to get it ready for paint, so I want to add any reinforcements there first before I paint. I'll do it one section at a time, but I would eventually like to brace the car as well as possible, *maybe* install a small 4pt cage (mainly because if I have a 4pt. harness, I want to have a roll bar of some sort), and then add some foam to the rockers and maybe the base of the pillars.

I know there are a lot of braces out there that don't do much, if anything. I plan on having my front and rear strut bar bolt in, but I would like to weld in any other braces under the carpet or other interior panels. Any ideas?

The Dark Side of Will · Mon Apr 09, 2007 5:51 pm

Triangulate, of course. Concetrate the effect of your additions to "box" open spaces like the engine bay.
Beyond that it's experimental. Remember the guy who put the Ultima in the USCC a couple of years ago? He made modifications to increase chassis stiffness, but had to build a jig and measure after each mod to see how much it helped and whether or not it was worth it.

crzyone · Post by **crzyone** » Mon Apr 09, 2007 6:41 pm

Would a full weld in rollcage not stiffen it up enough? Some strut bar braces and a roll cage should make it pretty darn stiff.

Fastback86 · Post by **Fastback86** » Tue Apr 10, 2007 4:06 am

Some one posted a good write-up on OE not too long ago about a little bit of bracing in the engine bay that goes a long way. He (I forget who it was) noticed that in the corner where the dogbone mounts, things are nicely reinforced by all the bracing needed for the dogbone. On the other side of the car, where all the cruise control stuff mounts (if you have it), there is no bracing, as there's no dog bone to keep in place. He found, through some interesting tests, that this was a weak point and prone to flexing and warping under stress. A few triangular braces in that corner did wonders for the rigidity of the engine bay.

Pyrthian · Post by **Pyrthian** » Tue Apr 10, 2007 8:59 am

easy way is to talk to other owners who have crashed/broke them.
next, is just plain old look. the longer a section is - the more leverage it puts against its joint. build a replica out of Elmers & toothpicks, and push against it. is it a unibody or actual chassis? another fun part is the direction of forces. many parts can be very weak in one direction, and take the weight of full thrust in the other direction. there is no "look for the yellow weld bead" answer.

The Dark Side of Will · Tue Apr 10, 2007 2:06 pm

crzyone wrote:Would a full weld in rollcage not stiffen it up enough? Some strut bar braces and a roll cage should make it pretty darn stiff.

That depends on where it's flexing. It may just push all the flex out to the remaining parts of the car's structure that are still original. If you add enough tubing to take all the forces on the chassis, why not just start from scratch?