The function of the semi-trailer suspension system is to minimize harsh movement and play an important role in protecting the semi-trailer and cargo. It determines the load capacity, maintenance cost, and driving stability of the semi-trailer. The entire suspension system includes components that connect trailers and trucks to the wheels. It can promote better driving quality and make trailers better handling.
As with most vehicles, there are multiple options for you to choose from when choosing the right suspension system for your trailer. There are two most common types: air suspension and leaf spring suspension.
Air Ride Suspension
In the trailer industry, air suspension is the most popular suspension, and currently about 75% of semi-trailers use air suspension. Although it was more expensive in the initial stage, it was worth it. Because the air suspension requires little maintenance and repair, and when you don’t need a semi-trailer, the air suspension also has a higher conversion value.
Its characteristic is to bring a smooth and efficient driving experience, no matter how heavy it is. When the weight on the trailer changes, the height control valve senses the movement between the axle and the chassis. When the movement is large enough, the system will send out more air pressure to the air spring to make the axle reach the desired height.
Leaf Spring Axles
This is one of the most commonly used axle types and is also part of the spring suspension system. When the semi-trailer needs to drive on uneven roads, the leaf spring axle is very useful. Because the system is curved, the wheels of the semi-trailer can be moved independently of the truck body.
Springs can be rated according to their stiffness, which is called spring rate. It refers to the force required to compress a spring by 1 inch, expressed in pounds per inch (lb/in). The lower the spring rate, the more comfortable the ride experience provided. However, this spring rate is not suitable for use in semi-trailers. Commercial trailers that usually carry heavy loads, especially semi-trailers, are suitable for higher spring rates.
Pros of leaf spring axles:
- Lower repairment and replacement costs
- More uniform tire wear
Cons of leaf spring axles:
- Rougher ride on uneven roads
- Metal parts may generate additional noise
Leaf spring axles are good for: Lowboy trailers, Flatbed trailers, Tanks, Dump trailers, Reefers dumps.
Load capacity of axles
The axle load capacity of semi-trailers is crucial for the transportation of heavy goods. This determines how much cargo the semi-trailer can transport. Usually, axle configurations are subject to legal weight restrictions. Before special permits were obtained, the average axle load capacity was usually 34,000 pounds. With the license, the average load capacity is 44,000 pounds.