How to Size Your Ramp Door Spring System

It is important to properly size your Ramp Door Spring System.  If the spring is too torque is too large, you will not be able to put enough turns on the spring to wind all the cable on the cable drum or the door will raise by itself.  If the spring torque is too low, the door will be too heavy to lift by hand and/or the spring will have too many turns.  The problem with too many turns, is the spring life is dramatically reduced and the door may be difficult to open.

A properly sized spring system will allow the user to lift the trailer door with one hand.  The cable will never become loose on the drum.  The door will open easily and not “crash” down.

Following are the measurements needed to properly size a spring system:

Critical measurements:

Springing weight – Weight of the ramp at the beginning of the spring cycle. Determined by placing a scale under the open door with no spring system attached.

Door Height – It is also helpful to know the distance from the top of the door to the end of the open door. This is an easy check to be sure the cable will be long enough. Standard cable lengths are 150”. Lengths of 110”, 125”, and 174” are also available and can be substituted in any standard system.  Standard M-3 drums require 13” of cable to remain on the drum when the door is open. This is a safety precaution that insures that the cable does not disconnect from the drum.

Header Width – Width of available headroom inside of the trailer. This determines the length of tube in the spring assist.

Frame material of trailer – Spring assist systems are built with either steel or aluminum weld brackets that attach to the header above the door frame.

Ramp door hinge style – M-3 spring assist systems are designed to be used on doors with pipe-style hinges attaching the ramp door to the trailer frame. If you have a torsion spring style hinge, please contact us.  They require some additional information.

Please use the following M-3 Spring System Spec Template to help us size your system.  Fill in the relevant information and send it to us.  We will respond with a system that will meet your needs.

At M-3 & Associates we strive to provide our customers with the best possible products.  We hope this information helps you put the best possible system in your trailer.  Feel free to contact us with your questions at

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