Q: The car vibrates at a certain speed

Hello. Since the vibration is vehicle speed sensitive, it is likely that it is related to the wheel/tire assemblies, driveline, and/or suspension. An expert would sequentially look at these systems to isolate the problem. The causes can be quite surprising.

A weak or failing shock or strut can account for this. In one notable case, I had a car equipped with new Dunlop tires that vibrated terribly. The tire/wheel assemblies all checked out perfectly on a calibrated balancer. It turns out the tire sidewalls were just too stiff in for that car’s specific suspension. Switched to Michelin tires and the problem disappeared instantly. You could try to have the wheel tire assemblies evaluated on a "road force" type balancer which accounts for variance in sidewall stiffness.

Tires might have unusual wear, often due to lack of rotation or misalignment, and this can cause vibration. If your wheel bearings have more than .002 inch of play, that could cause it as well. There could even be an issue with an unbalanced CV shaft or driveline, or loose u-joints.

Brake rotors or drums could be out of balance. To cover that possibility, you could try re-indexing (by one or two lug positions) the rotor or drum on the hub (try one wheel position at a time) to see if there is a reduction in the vibration. For help having this addressed appropriately, a professional from YourMechanic can conduct relevant tests to diagnose the vibration issue and advise on a repair.