Just about every car owner has experienced it: Your car is fine when driving around town at moderate speeds, the suspension smooth and comfortable. Then, at freeway speeds, the car begins vibrating so much that it threatens to knock your teeth out, not to mention the fact that it gives your passengers a real fright. There are multiple problems that can cause a car to vibrate at speeds of 65 mph and above. The best solution is to methodically go through the problem areas that could cause this condition.
If the suspension on your vehicle is out of alignment, it may cause the wheels to vibrate at certain speeds. Sometimes the vibration will occur at slower speeds, but other times will occur at freeway speeds, such as when you are driving at 65-mph or more. Poor alignment can be caused by running into curbs or by accidents that have bent suspension components or knocked them out of alignment. Worn-out suspension bushings can also cause problems. To determine if your alignment is incorrect, take your car to an alignment shop, where mechanics can check it.
If the tires on your vehicle are unevenly worn, they may cause it to vibrate, a problem that will become more noticeable at higher speeds. Unevenly worn tires can be caused by poor alignment or by an alignment that is not set to the factory settings. Tires that are worn excessively can also vibrate at speed. Have a tire shop inspect your tires and replace any that are dangerously worn or uneven.
Another potential cause of a shaking, vibrating car at freeway speeds are worn suspension bushings, such as ball joints and control arm bushings. For instance, BMWs are notorious for having worn-out control arm bushings, which can lead to shaking at high speeds and under braking. A professional mechanic should inspect your vehicle's suspension to determine whether there is excessive movement in the suspension from worn bushings.
The wheels on a car have a rough life -- they are exposed to potholes, bumps and curbs, and in the process can become bent. If they are bent, they will definitely cause the vehicle to vibrate at speeds. A visual inspection can be performed on the wheel, but the best way to determine if the wheels are bent is through use of a wheel balancing machine at a repair shop; the wheel can thus be replaced or repaired. Suspension parts such as control arms and tie-rods can also become bent from hitting pot holes and curbs, as well as a result of minor accidents. This may also cause a car to vibrate at 65 mph, as well as other speeds. Warped brakes rotors will make a car shake at high speeds as well, but this will usually happen when the brakes are applied.