OK...as far as stability goes, a triangle is much more resistant to stress/strain than a square. This is why even the typical ladder bar setup, although strong in appearance, has serious limitations in torsional (twisting) stress. Chassis designers say that by adding a few pieces to the chassis in the right places can dramatically increase resistance to torsion. Even a full nascar roll cage does not reduce torsional stress very well.

Every owner of an f-body (esp. convertibles) can attest to all the groans the chassis makes when cornering, turning onto an incline, etc..

About a year ago, I had some Alston sfc's welded in. Made the car feel much "straighter" when driving, but my convertible chassis steel seemed to lack alot of torsional resistance. So, I borrowed some of steve spohns SFC design and decided to triangulate the front subframe to see if there was any improvement.

All I did was get some 1" round 12 guage tube and some flat bar ($5). I had the tubing welded in at a right angle to the convertible ASC sfc and then to the point on the front subframe where the Alstons were welded (both sides...the 1" tube clears the cat well). I used a piece of 5/16 flat bar between the tubing and the chassis.

RESULTS: Very nice difference in handling. The front end seems like it wants to get down to business. No protest during hard cornering. The front end just feels "low and mean", especially at WOT. Easy mod for $40 (welding incl.).

Oh and this mod was made after Alston sfcs, 2-pt STB, wonderbar, and Eibach prokit springs, WS6 sway bars, poly bushings (not to mention boxed in LCA,s and a panhard rod.) I think that if you can feel a very noticeable difference in handling even after you've done ALOT to your suspension, its definately worth it.

If you have a vert its easy because you already have 2-sides of the triangle (factory sfc and the front subframe).

If you have non-vert, all you have to do is add about two feet of tubing under your door sill on each side to complete the triangle.

Anyway...I thought I'd share.

 

Sounds like a worthwhile modification.

Anything done in a flat plane has very little to do with torsional stiffness though. The best thing you can do for torsional stiffness is install a cage. Even then, properly triangulating it to resist deflection would make it nearly impossible to drive on the street.

BTW, after having driven a Winston Cup car I can say that they are about as stiff as anything on the planet. They are totally precise, totally predictable, and feel like you're doing 60 when you're really going 135! They test them for torsional stiffness by instering a long bar through the front and rear frame rails an aplying a 200 lb weight to the end of a 10' lever. Deflection is usually measured in thousandths of an inch! If that isn't torsional stiffness I don't know what is!

 

The bit about the Nascar roll cage was a model made from balsa wood with the same testing; a torqe arm with a weight attached. But, the design only included a bare bones nascar cage on a typical suspension and did not include all the extra trimming you'd expect to find in a race car. I believe you when you say how driving it felt. I'd love to get behind the wheel of a winston cup car . How did you manage that btw?



My goals with triangulation were to just increase handling/performance without sacrificing drivability too much. The front feels alot more solid now. Only problem is that I still get alot of window rattle/door creak. It bugs the crap out of me.

Now...I don't now wether to run 1.75" round 12 guage along the already present ASC (crap) sfc's or to just go ahead and install a 4-pt roll bar.

 

I drove a Winston Cup car when I was down in Florida at one of the Richard Petty tracks. All the cars are Chevy powered with different bodies. They limit you to 135 if it's your first time, but it was still a lot of fun. Once you are up to speed you aren't allowed to downshift, but even in 4th gear it would put you back int he seat without a problem. I have an open invitation to come back at any time and take the advanced course, where the rules are a lot more lax. It was pricey, but one of the best experiences, and in my opinion well worth it.

To stiffen the car up further you would have to use a rollbar. It sounds to me like what you really did was keep the shock towers stable under cornering loads, which significantly improved handling, but in order to really tighten up the car you will have to triangulate the structure to a central hoop.

 

can you post pictures??

 

yeah, can you post some pictures? i'd like to see that.

 

Sorry for delay...here it what I have

 

Thats how the Spohn's would look with the lakewoods. I missed that you were modifying factory convertible SFC's

 

pretty much what Im doing with my vert. Im actually cutting out the stock pos rivited on sfc metal. and taking the box tube through the sheetmetal. and tieing my 8point cage into it.

 

TPI 383...do you have that 8-pt installed yet? If so...how did it help with chassis flex?