I remember a long time ago someone said they put that expanding foam in the...I forgot what it's called...where the side skirt attaches to, and it made the car noticably stiffer.


I found this. When I get the money, I'm gonna get this. It's $184 for front or rear. Not too bad. I hate the flexy chassis.


Here is the link. Scroll down halfway and you'll see Tanabe Sustec.

 

that should help with a bit of the suspension flex, and a little with the chassis, but to really get the chassis stiffened, you're going to want to add a roll bar/cage. I haven't found one prefabbed for a sol, so for my race chassis, we're building our own

 

...As much as I'm sure my car's structural stability would benefit from a rollcage, I just can't stand the way they look. Blech...to the power of three.