I recently bought a 01 4.4i in April and everything was fine. Handles great and smooth as butter. I started noticing that at around 80mph, the steering wheel would shake a bit and I felt it from the front. So I was guessing it was due to alignment.

Now recently I just installed 215s and put on 275/40's and 315/35's and still had the shakey steering wheel but this time at lower mph (around 40-50).

I got the car aligned and it's still the same issue.

Can someone give me some ideas on what it an be before I go to the mechanics. I really don't want them giving me a different solution when it's really something else.

--- I was thinking that the tires were not balanced properly.
Can a unbalance tire cause this to happen?

Thanks