Modern buses have either mechanical or air suspension system. Air suspension makes use of air springs. The air springs, which are also referred to as bellows are filled with air using an engine-driven compressor. The amount of air inside the bellows determine the ride height and spring rate. This adjustability gives air suspension significant advantages over mechanical suspension system. Its adjustability allows the air suspension system makes to maintain ride height regardless of the load. This is done by varying the pressure of the bellows. The ride height can be raised above the normal height to provide enough clearance when going over steep ramps. It can also be lowered to make it easier for passengers to get aboard.
The adjustability of the air suspension system is also very important for comfort and performance. It provides a smooth and consistent ride quality. Passengers can get to their destinations fresher. It also help reduced driver fatigue, which is great not only for the health of the driver but also for road safety. After all, less tired driver can focus more.
Air suspension has been around for over a century. However, air springs have only become viable springs for bus and other large vehicle in the last two decades. Compared to conventional suspension, the air suspension was less durable. This is just the nature of the bellows which are made of reinforced rubber. It required more upkeep and had higher chances of causing problems on the road. It was not until stronger bellow materials were developed that the air suspension has really become a standard in modern buses.