Stiffening Up A Ladder Frame

I once did a trunk hoop in an e30 Cabrio and tied it in several places on the rear seat bulkhead.  Not sure how much it did but SOTP it did feel a little less shaky.

Vertical plane is the key I would think.  If you can tie in some steel hoops behind the seat and at the firewall, you might get what you need

One alternative I've always wanted to try is use a suspension design philosophy that doesn't require chassis torsional stiffness.  The purpose of a torsionally stiff chassis is to be  able to transfer load diagonally in the vehicle.   In FSAE (in the early 2000s before the auto industry went chassis stiffness crazy) the rule of thumb was make the chassis at least 10X stiffer them the difference between front and rear roll stiffness.  You could  make a suspension that doesn't require significant cross car weight transfer.  Higher roll centers, high spring roll stiffness without use of sway bars.  It might not be as good as a fully optimized stiff chassis but it may be faster overall then adding all the weight required to make a ladder frame stiffer.

Three wheel vehicles (2F1R) demonstrate that reasonable performance can be reached with no ability to transfer weight across vehicle.  As long as your front and rear suspension mounts are stiff enough that geometry could be maintained I would think you can be successful. 

In reply to nocones :

Are high roll centers and stiff springs actually different in this context from sway bars? These are all mechanisms for affecting the roll stiffness at each end.

Or am I misunderstanding?

In reply to nocones :

The downside of high roll centers is the weight jacking issue. The suspension geometry required for a "high" roll center makes your instant center (point in space where the control arms would meet if they were extended out) become very high off the ground. As a result of this the slope of the n-line (that lower red line in the diagram) is very steep. The cornering force exerted over the leverage of that steep n-line acts to raise the car, lift the inside wheel, and transfer a lot of weight to the outside wheel. In fact, any car with a roll center above ground will have the center of gravity raise while cornering!

Since we're starting to go on the tangent of experimental projects, I want to try a longitudinally interconnected z-bar suspension setup. Imagine a sway bar with one of the ends rotated opposite of the other, this is the basis of the "z-bar" concept. There are many other ways to implement this too, such as leaf springs, hydraulics, linked coil springs, etc. While a traditional sway bar allows motion on both sides in the same direction and resists opposite motion, the z-bar allows opposite motion and resists similar motion.

Now imagine taking your car, throwing away the traditional sway bars and connecting a z-bar front to back on each side of the car. This does a very efficient job of controlling roll without the clumsiness of traditional stiff sway bars. Another benefit of this is you have a suspension that conforms to the road better. On uneven roads or hard cornering it would be very difficult to ever lift a wheel! With traditional suspension systems people will spend large amounts of time corner balancing their cars to the nth degree but with stiff suspension even tiny variations in road flatness will cause huge changes in corner weights. A z-bar suspension will articulate and maintain even weights much better. In fact you could even get rid of all the corner springs and put in one lateral z-bar (most likely on the heaviest end of the car) and have a vehicle that is perfectly sprung with only three springs! It's pretty mindbending!

In reply to nocones :

The problem with that setup is that I would be at the mercy of whatever my stock ladder frame was doing. With no way to control it. And if I modify it, I'm back at square one.