I drive a 2008 Ford Mustang, when I get to 55 to 60 mph the car starts to shake pretty bad but as soon as I hit 70 the shaking stops. What would be causing the car to shake?
A tire out of balance could cause that. So could a failing center driveshaft support bearing.
I will ask if your car has springs that lower it. That can throw the driveline angles off and cause a vibration at a certain speed.