» » Torsion Axle – everything you want to know

Torsion Axle – everything you want to know

Boler Axle

The original Boler came equipped with an Ingersoll Rub-R-Ride rubber torsion axle and later was replaced with the Dexter Torflex. Rubber torsion axles are a good system that requires little servicing other than the usual bearing repacking and maintenance. One very unusual aspect is that the axle in the Boler is actually installed backwards. These axles are designed to be installed so that the suspension arm trail behind the axle tube, the wheels are pulled behind the axle, but the Boler designers saw the opportunity to install the axle tube behind the step in the kitchen leading up to the dinette area, but to locate the wheels in the correct location for proper trailer balance the suspension arms need to point forward (called a leading axle), the wheels are essentially being pushed down the road ahead of the axle.

There does not appear to be agreement on what the original Boler used as the start angle, I believe the angle they used was a 0° or 10° up angle but this I cannot confirm. An initial setting of zero degrees or a slight up angle will maximize the suspension geometry and provide the smoothest ride. The reason for this is that when the arm is positioning upward and being pushed down the road the impact or compression of the suspension arms arcs toward the rear of the trailer following the direction of travel, if the suspension arms are is positioned at a down angle any compression actually forces the wheel forward against the direction of travel which results in a harsher ride.


Replacing your Axle

Over time the axle will wear out, the rubber elastomer will deteriorate with use and age.  As the elastomer deteriorates the axle will start to sag, causing the trailer to sit lower, there can also be movement laterally in the torsion tube which will cause the wheels to toe out, this can cause slight swaying and tire wear. The most noticeable result will be a harsh ride, often noticed by seat cushions flying everywhere, cupboard doors open and even bouncing of the trailer even when the road appears smooth.  As a general rule of thumb an axle that is 15-20 years old probably needs replacing.


How do I check my axle for wear?

According to the Dexter engineers “Dexter would consider any Torflex arm that has moved more than ten degrees from the original build angle as weak or losing suspension”.  But how would you know if your axle has sagged 10° or more when you don’t know what the start angle was?

The first test is to jack up each side of the trailer and watch to see if the wheel moves down as weight is removed from that side, if on either side the wheel does not drop at least 1½” the axle needs replacing.  Second, measure the diameter of your tire (as an example ST175/80D13 trailer tires have a diameter of 24″) and divide this number by 2 (in this case 12″).  Now with the trailer sitting on level ground measure the distance from the ground to the top of the axle tube, either just ahead or behind the axle mounting brackets.  Take the tire radius and subtract the frame to ground measurement, if the result is greater than 2½” your axle needs replacing (the above calculations are based on a fully loaded axle with an initial start angle of 0° to 10° up angle).

First measure the diameter of tire and divide by 2 to get the radius

Measure from the ground to the top of the axle
If the measurement (Radius minus height) should be the 2.5″ or less.

In the above example R=12″; Frame to ground = 11″ (12″-11″=1″ axle is good)

As an example: your trailer has ST175/80D13  tires which have a diameter of 24″, dividing the diameter by 2 gives you the radius of 12″.

The distance measured from the ground to the top of the axle measures 7″

12″-7″=5″  The axle arm has dropped more than 2″ and should be replaced

How do I order an Axle?

When replacing your axle there are a number of items to consider, these include:

  • Axle weight capacity
  • Axle arm start angle
  • Axle bracket spacing
  • Hub face to face measurement
  • Brakes
  • Axle type or manufacturer
  • Axle orientation (leading arm vs trailing arm)