Shaking at 45 MPH and stops after 50 MPH?

Yep, I have seen bad front tires cause this issue. I would raise the front of the car and then rotate the wheels and look for anomalies in the tread pattern lets you know the tire has come apart internally. Please check out these guides to help you.

https://www.2carpros.com/articles/steering-wheel-shakes-when-accelerating-or-braking

and

https://www.2carpros.com/articles/how-car-tires-work

and

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.