Lincoln Vavigator 2003?

The best car, by far, I have ever owned. In fact, this is Navigator No. 3 for me... (Thank you very much) - This car rides like a boat. I can go a mile without touching the steering wheel and it stays its course, straight down the line. The ride is soft, and just plain awesome; However, if I make a tight turn (Like a 360) and pushing the steering wheel to its limits, the car wobbles - as if a wheel is about to come off. What is it?