We are accustomed to think of air as being light and do not associate it with much force. Of course we do read about hurricanes and typhoons where air in the form of gales is able to cause big damages by being very forceful. But these gales are of very high speed which we will usually not encounter while driving a car. But aerodynamic forces are significant even at lower speeds and you can use that fact to your advantage. To give you an idea first you should know that air isn’t quite as light as you think. In a room that is 5 meters wide and 5 meters long and 3 meters high if you were asked to guess how much air is there you will likely think that a figure of 80 kilograms would be too large. But the fact is there is more than 90 kilograms of air in that room at normal temperature and pressure. And that is the reason why even at speeds of say 40 miles per hour the aerodynamic forces start to become significant.
So how can you use these forces to your advantage? Well when your car is moving at a high speed there is a tendency for it to take off whenever it hits a small imperfection in the road. This makes controlling the car at high speeds difficult and unless the road is pretty much flawless you will need to drive much slower than you otherwise might. At such a time you would like it very much if there was something that would push your car down without making it slower, so that if it met an imperfection, it would take it into its motion without taking off much at all. And that is what car spoilers help you to do. It is a very elegant solution that you can see on racing cars as well. It produces a downward force that is proportional to the speed of the car. You can also make you car even more stable with other products such as lowering springs which reduce its center of gravity.