Howdy,

...this might give the car greater torsional rigidity...

Properly designed and implemented bracing will improve rigidity. But why do you need a stiffer chassis? Are you going to be racing? If so, will the rules allow chassis modifications?

For commuting and touring, after nearly 45K miles, I have not noticed excessive flex. Directional instability due to crosswinds and truck wakes, yes. Excessive roll (stock anti-roll bars), yes. But if the chassis does flex, I have not noticed any ill-handling because of it.

Do you have handling problems? Renew all the bushings, shocks, springs, and install larger anti-sway bars. If you have already done all that, post back with the specific problems you've noticed. Maybe someone can point right to the reason why.
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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 53 year old fat man. ;-)