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Depends what the car will be used for. All out racing, street/road course/autocross, or street only with some spirited driving? Too stiff and the car will 'hop' and 'chatter' across the road or track.

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That is the spring and shock combination creating the "skipping" Best case is the chassis is as stiff as it needs to be (pretty ombiguous answer). But meaning just as much stiffinng (weight) to make it stiff and not just have a heavy overdone tank out there.

Bob Reed has SCCA GTII championship under his belt and thinks his you reach a limit with these old cars because it lack a full cage. He can cut as fast laps with his 300 SRT-8 as his 68 Barracuda .

But Bob has driven Tiim Werner's 68 Valiant for comparison with full cage and thinks that the cat's meow. Especially with big 1.10 or larger T-bars

That's one person's take on it.

This is Tim's Valiant in action...

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Taking chassis flex out of the picture will rear the ugly head of inadequate suspension components.

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My point was that a stiff chassis will need absorbtion from its suspension. I stiffened my front unibody up a bunch and it is now glaring that I seriously need bigger tbars and better shocks bigtime.

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Are you sure about that, because as I understand it, if we are talking the about driving the same circuit, and the only change was to stiffen the chassis, it would seem some of the compliance was taken out of the suspension equation, meaning a softer set-up would be needed to have exact same performance, am I missing something?

Do you mean stiffen to maintain correct geometry?

Suspension tuning is based on compliance and resonance of all springy parts, tires, tire pressure, TB, shocks, bushing compliance, control arm compliance, chassis compliance, etc. If you make one stiffer, some other combination needs to be softer to maintain same ride quality.

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Autoxcuda:

That photo that you attached is stinkin' awesome.

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This new forum is really getting me interested in cornering performance again!

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Here is a shot of the front down tube. I think that the down tube needs to be tied into the shock mount so that might be one of the mods that we add this winter. Just a couple of pieces of steel tying the shock mount to the sheet metal and the roll bar tube should do the job.

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My point was that a stiff chassis will need absorbtion from its suspension. I stiffened my front unibody up a bunch and it is now glaring that I seriously need bigger tbars and better shocks bigtime.

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Are you sure about that, because as I understand it, if we are talking the about driving the same circuit, and the only change was to stiffen the chassis, it would seem some of the compliance was taken out of the suspension equation, meaning a softer set-up would be needed to have exact same performance, am I missing something?

Do you mean stiffen to maintain correct geometry?

Suspension tuning is based on compliance and resonance of all springy parts, tires, tire pressure, TB, shocks, bushing compliance, control arm compliance, chassis compliance, etc. If you make one stiffer, some other combination needs to be softer to maintain same ride quality.

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I have lots of pictures of Tim's car since the last couple of builds were done in my shop. Here is a shot of the XV brace up front. You can also see the down bars in the engine compartment.

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How important and what is too much?

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Makes perfect sense to me....

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Then consider this, say we have a car that you are going to stiffen up the chassis by any means you desire. Say you want/expect the car to have the relative same handling characteristics after mods are completed ( and as mentioned a post or two before chassis stiffening will make car more consistent/predictable).

So if for simplicity we imagine the car has say 4? "springs" of different rates/resonances IE tires at a certain pressure, the TB's, the chassis flex (which really is a spring as long as it returns to original shape after removal of road loads) and the drivers seat suspension. To keep matters very simple. If all these "springs" say add up to some magical value "X", removing or reducing any of them will reduce the "springiness" of the system, and in order to keep the same ride stated above, something or combination needs to be soften to maintain same ride quality. However without any readjustment, the suspension being more rigid may exhibit less shake feel more predictable, and allow an increase in other "spring" rates until chassis flex(spring) reappears due to greater loads or another spring becomes too soft for the new application.

Bottom line, increasing Chassis stiffness does not automatically require increase spring rates for same ride, and that makes sense to me, and I guess we still disagree