I have 33" tires and mine definately has the shakes at 40-45, I tightened the steering before (a year ago) and it seemed to work for a week but it came back. I guess I just learned to deal with it but it is VERY annoying when others are in my car and I look like I am suffering from parkinsens with the arm shaking like crazy. I can white-knuckle it and minimise it but then I get a clicking noise from the wheel trying to go back and forth and it feels bad so I just learned that that is the natire of the beast, if anyone figures it out I really want to know. With stock tires/rims I never had this problem so the tire or rim could definately be the culprit in your case.