I have never driven a Honda s2000 But I am willing to bet that if the rear control arm mounts were stiffened up like I stated earlier you would probably find the Solstice will have better handling then the s2000. The reason why I state this is because of how the shocks are mounted on the s2000. they are mounted on one side of the control arm and not in the center like the solstice is.
Here is a shot of the rear suspension of an s2000. the open hole in the control arm is where the coil over is bolted in.
and here is a shot of the solstice rear suspension.
In the picture of the Honda you will notice the lower control arm mount point is right at the bottom frame rail.
for the Solstice you can see the frame rails above where the sway bar attaches.. Now look where the lower control arms are attached. and that stock black beam you see is mounted to close to the frame to stop the flexing that happens where the lower control arms attach.. the front of each control arm is attached directly below the frame but that back is far below it and there is no support between the rear mounts that would keep them in place.
Do this is a test with your own vehicle. Jack the car up and let the suspension hang. take a piece of tape and run it between the 2 rear control arm mounts. then lower the car back down.
The tape is going to break and it's not by a little either. If you bring the tape back together you will see a hell of a gap between the 2 ends where it broke. This is only flexing caused by the weight of the car when it is stationary. Now imagine that with lateral forces pushing on it. It is going to move a whole lot more then just the weight of the car sitting on the suspension.
I just picked up a piece of 3" x 36" x 1/4" steel flat bar to join the DDM Works pro beam and the modified Werks frame brace together at the control arm mounts. I am going to use grade 10.9 bolts to bolt the steel. There is going to be quite a bit of sheering forces this is the reason why I went with grade 10.9. Tomorrow when I list the car back up to make the 2 pieces I am going to bolt in I will take some measurements and tell you how far from the frame that control arm mount is. From there we can calculate how much twisting force is applied to the rear frame.
There are calculators available online to get rough estimate of the lateral forces. and I guesstimated the distance at 10"
Cornering force is the lateral force produced by the vehicle while cornering. It is also known as the side force and is a force which is exerted parallel to the road surface.
in Static friction coefficient enter 0.9. this is for dry roads.
gravity acceleration I entered 55, this is the slope in which the vehicle would slide without moving at all. so on a 55 degree slope is about where I think the car would start sliding.
Mass of vehicle I entered 2900 lbs
the radius of the corner I entered 60 feet
slope of road I set at 1 degree
The maximum speed going through the corner would be about 71mph
the lateral force would be somewhere about 73473 newtons. Divide that number by 2 (front and rear tire). and you get 36736.5 newtons.
Now we want to convert that force into lbft of torque. because this is essentially what is happening to the frame rail
In Force enter in 36736 newtons
in length enter in 10 inches
and you get 6882.15111 lbft of torque. Now I know this is not a perfect calculation and it is actually impossible to get a perfect calculation, But it does paint a good picture as to what kind of forces we are talking about. The torque stresses that the frame is seeing are massive. So we know the frame is twisting and this twisting lets the control arm mount flex, and it lets it flex a lot!
just converting the newtons to lb force (8258 lb force) shows what kind of force is taking place on the control arm mount.
The front suspension is in better shape then the rear, There are stock cross members at both the front and rear control arm mounts. I added the shock tower brace from Werks and also the front frame brace. These 2 components help reduce the amount of twisting the front frame is going to see.