I have seen the subject briefly discussed before but I'm interested in reading members opinions on the matter.
For example, lets say that a car has all the bolt on upgrades that are available to him/her. Bigger torsion bars, sway bars, shocks. The body has no frame connectors, torque boxes or nonstock gussets. Now add in a welded K member, welded frame connectors and torque boxes, LCA stiffener plates and even the triangulated cowl to fender apron brace. Does this mean that now with the cars "foundation" being a much more solid platform, that the spring rates feel firmer? I've wondered if the reduced body flex equates to a driver actually feeling the potential of the T-bars/leafs spring rate? Who has some insight or opinions on this matter? Thanks, Greg

We raced A Bodies & E Bodies on the dirt in the 70's & early 80's & I know when you stiffen a car you take the spring out of the car

Surely someone with a set of scales has pondered this!

I know that when you stiffen that car you feel the difference It's been too many years now

Good question
Unless you have a way to "test & verify" it's unknown what you have...most combinations are unknown and untested.

Testing is not the autocross course either, it's hot laps on a road course you are familiar with so you can determine if the car is rotating thru the turns and if your lap times have improved. Top speed on the straights is determined by how fast you cut the curves.

It's how all the parts work together under duress.

Like BB & jcc are saying, once you take the chassis twist/flex out of the equation, it should take less spring rate to keep the tires in contact with the road. Flex/twist acts like another spring, and it upsets applying the tires consistently, as the chassis winds up & releases. You can't really analyze your suspension setup until you address the chassis stiffness and remove that variable. If you're unsure whether your spring/shock/bar package is optimum, a starting point would be what a similar (weight, tires, power, chassis, wheelbase & track width) car is running to get fast laps, and tune from there. Your setup may vary a bit depending on how much rotation you like, your powerband & gearing, and different track layouts. The clock is the final judge, but it's important that the car isn't fighting you by wearing you out keeping it at the limit.

Ive talked about this in another thread,but, in my experience although the car rides and acts stiffer, I feel I am in need of bigger tbars and better shocks more than ever. Doesnt make sense to some, but the bottom line is if i was building a car, I wouldnt dial in my rates until the chassis was stiffended to the point it was going to be used in first.

SB412Duster is the only chassis guy that I know here that's setup circle track & drag cars
He's an original trial & error guy & has a brain full of knowledge. He may can answer the question

I added weld in frame connectors, and torque boxes to a '70E. There was a noticable difference driving it before and after with 100% stock suspension. Also a noticable difference jacking it up. Before the upgrade, jacking one corner would visibly twist the car. After it would not.

Then I upgraded to big T bars, sway bars,XHD springs and welded.gusseted K. With the heavier springs, I am sure uneven ground, bumps or cornering loads would twist the frame... I would loose some benefit of the better pieces and eventually crack the unibody.

I am sold on the benefits of the chassis stiffening.

I also believe that "balanced" stifffening can greatly improve handing without making the car unpleasant to drive. "Balanced" meaning frame, springs, sway bars, shocks and tires stiffened up together. If only one or two of those elements are stiffened a lot, there is good chance handling or ride or both will suffer.

Biggest benefit has got to be a consistent spring rate, rather than the ability to change your spring rate.

I JUST got back from driving the car after it had been on jackstands for over 3 weeks. With limited time after work and the fact that I hand fabricated everything, I'm okay with how long the job took.
What started all of this for me was that my Charger had the tendency to oversteer when pushed hard into a corner. It didn't matter if I was going uphill or down, coasting or on the brakes. Certainly it was worse under throttle, given the power and the Sure Grip differential. I was and still am leaning toward the belief that my roll stiffness is out of whack, with the rear having a higher rate than the front. With that in mind I know what I can do: Either increase the front or decrease the rear. A tail wagging car is the hot ticket for competition 'Drifting", but for street duty I want the car to be neutral. If I want to hang the tail out, I'll lean on the loud pedal. I've considered switching the end link bushings to rubber since I have a few complete sets here. I also have a few other sized rear sway bars to test. One member suggested to disconnect the rear bar and tie it out of the way, then test it. Good idea, and its free!
Heres something though that I didn't expect. The car actually rides BETTER than it did before! It soaks up the road dips and bumps as if they weren't even there. Whatever squeaks and rattles the car had (Very few) are now gone. I didn't get to push the car very hard during my drive, but it appears that the frame connectors and torque boxes didn't affect the oversteer condition. I don't expect the reinforced K member install will make a difference there either, but I'm still going ahead with it. The improvement in ride comfort alone made the effort worthwhile. With some trial and error, I'll get the car to handle right.

"I don't expect the reinforced K member install will make a difference there either, but I'm still going ahead with it."

Frankenduster you will be surprised...maybe even amazed. Be sure to lovingly install the k member and lube the threads on the 4 large bolts and use a torque wrench. Keep up the good work

I DO expect the reinforced K member to improve steering response and accuracy, but it's the oversteer aspect that I expect to require a different approach. I welded the seams and added a 5/8" skidplate, but I still need to add the washers over the LCA and strut rod holes. After that it gets semi gloss black paint, since I can't seem to bring myself to install a dirty or unpainted part.