Problem with bump-steer in C4

I have a 1999 C4, in which I just put turbo struts/springs. The car looks very good lowered like this, however, there is a bump-steer problem, in that when I hit a bump, the car veers suddenly and dangerously. I was told various things, to include: it needs camber plates to adjust the camber; it needs 18" wheels, not the 17's that came with it from the factory; and it needs the Stomski SR083 tie rod ends. Does anyone have any experience with this, or have suggestions? Here is the description of the part from our host. DESCRIPTION Stomski Racing Front Tie Rod and Bump Steer Kit Based on the same technology as STOMSKI RACING's Rear Toe Control Arms, our Front Tie Rod and Bump Steer Kit allows for a full range of toe adjustment, as well as bump steer correction. We use aerospace quality rod ends and components to provide for the most durable, accurate part available. Also included are seals to protect the monoballs in the harsh exposed environment. Fits the 996, 997, Boxster, and Cayman.

I have a 99 C4 also. 122500 miles on it. The only suspension mods are H&R springs and 19" Champion wheels with Potenza's for summer tires, 18" and Blizzaks for winter / rain tires. I have experienced something similar, but i might describe it as more of a yawing motion. I have been blaming it on the age of my shocks. A secondary problem that seems to have made it worse is that my tire guy and I didn't pay enough attention to tire circumference. The Potenza's are 80" front and 81 5/8" back. This seems to have made the yaw worse. Makes carving on ramps interesting:-) and dicey:-( Does anyone know the max recommended difference between front and rear circumference? Tire pressures also seem to be a factor. I get the least yaw / bump steer with 4.5 to 5 pounds more in the rear. Right now I'm at frt. 34 / rear 39 psi. highway commuting. when it dries out a little more (2-3 month here in the NW:-( ) I plan on some testing a one of the huge industrial parking lot near by. Throwing money and PSS10 at it is not an option for now. Maybe later.

In reading about the problems associated with lowering the car, the number one problem is the change in the geometry of the suspension, usually at the tie rods. So, when you hit a bump, the steering goes whacko -- making the car suddenly veer off. The solution seems to be simple -- longer tie rod ends offered by Rennline as well as Stomski (I think both are offered by our host). They are very expensive -- about $200 EACH -- and you need at least the 2 front ones. BTW, tie rod ends and their adjusting tubes are about $40 normally, but since these are made out of billet metal (aluminum or steel?) and since they are for racers, there's a "market adjustment." Too bad the Chinese haven't entered the market, huh. Matter of fact, I better check the Goingsuperfast.com website if they are in production...

Any opinions about hiem style ends vs. the enclosed ends like i see on the Elephant Racing ends? My car is a daily driver thru the winter and it seems to me that the hiem joint might have a shorter life due the the location and grime than can get in to the bearing surfaces. There is a definite ouch factor to the price. but it's lower then the result of stepping out into a jersey barrier.