Steering Whell Pull and Shake(Shimmy)

Hey everyone I got a question. I have gotten my car aligned and all the tires balanced and when I got over 50 mph the steering wheel starts to shake(shimmy) and it also pulls with every bump in the road. I am not so much worried about the pull because the low profile tires more than likely cause that but what about the shake? Has anyone else had this problem and is there a solution. I read in a previous post the low profile Kuhmos have done this to others and this is the tire I have now. Is it really the tire or is there another cause to this. Any help to stop this would be great. Thanks