Today We’re Discussing Beams and Beam Ratings on Flatbed Trailers

The beams on your flatbed are essentially the backbone of your trailer. A pair of longitudinal support beam sections running under the deck the length of the trailer connects the front approach plate, the suspension hangers in the rear, and all the cross members run through it.

Here, we’ll look at the different flatbed trailers, their beams, and how they might affect specific applications for hauling. Some questions we’ll answer are:

  • What is a coil package on a flatbed?
  • Why are some semi-trailers bowed?
  • What is an extended flatbed trailer?
  • What is a beam rating on a flatbed?
  • How can I increase my backhaul options on my flatbed semi-trailer?

The 2 Types of Beams on a Flatbed Semi-Trailer

  • Aluminum Beams – found on all-aluminum trailers
  • Steel Beams – found on all steel and combo trailers

All-Aluminum Trailers:


Aluminum flatbed with arch in beam and no cross members.


  • Aluminum trailers are lighter and less rigid than steel trailers, and their aluminum beams flex more than a steel beam. So, aluminum beams are designed with an arch (Camber), and as the trailer is loaded, it begins to flatten.
  • This arch might not be ideal for transporting long flat materials though dunnage can be used to help fill that gap between the trailer’s arch and the product.
  • Aluminum flatbeds typically do not include cross braces, as is found on a combo trailer that has a steel beam.


Combo Trailers:


Photo of combo flatbed semi with cross braces.


  • A combo trailer has less arch (Camber) due to the steel beam.
  • The combo trailer typically includes cross braces for additional support. The weight of the load is distributed through the cross braces and back to the steel beam itself.


Which Beam is Right for You?

The answer will depend on the needs of your application.

A semi-trailer beam rating is defined by the maximum weight that can be loaded onto a 4 ft. section, and beam ratings run between 52,000 lbs. to 80,000 lbs.

For example, if you’re hauling concentrated loads like coils or concrete, we recommend going with a heavier beam.

It’s important to choose a trailer with a beam rating that will allow you to haul any load and not limit your options by starting with the wrong back-bone of the trailer.

Options to Increase Your Back Haul Opportunities.


Flatbed semi trailer hauling a coil.


Add a coil package.

A coil package is a necessary upgrade if you’re regularly hauling coils.

Aluminum trailers, including MAC, can be fully customizable to your specific hauling needs, including multiple hauling packages.

The Utility 4000AE comes standard with a 47,000 lb. coil haul package, with (9) 4” aluminum full-width tapered cross bars on 8” centerlines that provide optimized strength for the coil haul package.

Choose a heavier beam.

Upgrading from a 52,000 lb. beam to a 60,000 beam increases your backhaul opportunities and adds only about 300 lbs.

Options for Hauling Specialty Loads.

Wide Loads:

Wide loads are any load more than 8.5 feet wide.

  • Add additional cross braces for added strength.
  • Add wide-load amber and red lights to the front and the extreme corners and extension of the load as required.

Over Length Loads:

  • Consider an extendable beam trailer that will extend your trailer’s loading capacity from 48’ to 80’ or more.

Dedicated Coil Runs:

  • Add additional coil packages if you are running dedicated coil runs and not limit yourself to just one coil package.
  • Consider adding coil packages the length of the trailer. 

If you’re running specialty loads, talk to your flatbed trailer sales specialist to help you choose specs to optimize your options.



Read more in this series, How to Buy the Best Flatbed Trailer.



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