The pros and cons of overslung and underslung axles

Feb 10, 2023 | Spring Axles, Trailer Axle Kit, Trailer Axles

The following guide answers the question: What’s the difference between overslung and underslung axles?

Overslung and underslung refer to the position of the spring to the axle beam. In overslung suspensions, the spring is on top of the axle beam, whereas in underslung suspensions the spring is below the axle beam. See the illustration below.

overslung vs underslung springs

overslung vs underslung springs

Overslung axles

An overslung axle refers to the leaf spring that is attached to your axle. On overslung axles, the leaf spring is positioned over the axle. 

The leaf spring is a series of curved metal pieces that are clamped together. These metal pieces provide suspension. Suspension is important because it is the system of shock absorbers that allows your vehicle or trailer to ride more smoothly. With the suspension, the vehicle is cushioned from uneven roadways, bumps, and potholes. 


  • Greater ground clearance
  • Higher frame
  • Better on rough terrain


  • Less stability
  • Little to no sharp turning ability

What type of trailers uses an overslung axle?

Choosing between overslung and underslung trailer axles depends on how you plan to use your trailer. Because overslung axles are ideal for rough terrain hauling, these axles would be a good fit for agricultural or livestock trailers because you are often hauling on uneven ground, muddy fields, or gravel roadways.  

Underslung axles

In underslung suspensions, the spring is under the axle beam. As the spring deflects and the balance beam rotates, there needs to be clearance above the axle in the chassis for travel.


  • Great stability
  • Better on winding and twisting roads


  • Less ground clearance
  • Not ideal on uneven ground

BlueSwift Axles is the Trailer Axle Expert

Underslung trailer springs are much more common than overslung. But, really the key difference is that overslung axles raise the height of your trailer. 

If you’re unsure if overslung or underslung springs are the right choice for you and your trailer, give us a call today to discuss. We’d be happy to take a look at your current trailer axle situation and provide you with the best option to fit your hauling needs. Give us a call today to get started!