High speed vibrations Options

[Coligion]

My car just hit 96k miles, but this high speed vibration issue has always been a problem. When going over 55 mph, I'll get a ton of vibration from the steering wheel. I do have aftermarket wheels/tires. When I first bouht the wheels, I did not have centering rings and believed that would solve the problem. No dice. Even after getting the correct sized rings the car still vibrates. Before getting the rings, I did have the alignment and the wheels balanced. I wouldn't think inserting plastic hub-rings--in the center of wheel--could offset the balance, right? The shock/struts are relatively new, so it couldn't be that. Also, the car had this vibration problem even with the original wheels....Any helpful advice is appreciated.

[Coligion]

I had mentioned the centering rings as possibly being a culprit in the first post, but I later dismissed the idea after supposidly getting the correct sized rings. After looking at them further, I still feel they are not as tight on the hub/wheel as they could be. So, instead of ordering new rings, I used thin, invisible tape and lined the insde of the hub. After re-inserting the rings, they are now much more snug and secure. I did this to the front wheels first and later drove on the freeway. I could definitely feel an improvement. I just got done doing the backs, so hopefully I will see some more slight improvement.