One of the most common reasons why a car shakes is because of an issue with the tires. If your tires are unbalanced or if they are worn down unevenly, it can cause your car to shake. Another common reason for shaking is because of a problem with the brakes. If your brakes are worn down or if they are not working properly, it can cause your car to shake. Additionally, if your car is low on oil, it can also cause your car to shake.