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.