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 Redneck Trailer Supplies

RTS 101: Axle Assemblies

RTS 101 provides basic trailer parts information for the DIYer or business owner. For more information, please call Redneck Trailer Supplies toll free at (877) 9 REDNECK (973-3632).

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What are the two major types of axles for utility/industrial trailers?

Leaf spring (tube) and torsion

What is the major difference between a leaf spring axle and a torsion axle?

A leaf spring axle requires a separate suspension system, which is comprised of leaf springs and hangers that must be mounted to the trailer. Torsion axles have an integral rubber suspension system built into the axle beam.

What are some of the advantages of a leaf spring axle versus a torsion axle?

Leaf spring axles have replaceable suspension components, which are generally readily available from multiple sources.  In addition, these suspension components can often be quickly replaced in the field.  On the other hand, many times when a torsion axle is damaged, the entire axle must be replaced, leading to an additional investment and higher cost.

Can leaf spring axles be mounted directly to the trailer frame?

Yes. However, Dexter Axle (Redneck’s axle supplier) does NOT recommend this type of mounting directly to the frame. When this is done, the load is transferred directly to the frame and usually results in a very harsh ride. In addition, total axle capacity is also reduced by at least 50%

What is the difference between “overslung" and “underslung” axle mounting?

These terms refer to the position that the leaf springs are mounted to the axle. With “overslung” the leaf springs are mounted over the axle tube and with “underslung” the springs are mounted under the axle tube. “Underslung” mounting results in a lower deck height.

What is an axle spindle?

An axle spindle is the end section of an axle where the trailer hub is mounted.

What are three ways that a trailer manufacturer might use to change the trailer frame height when using a leaf spring axle?

By using a straight or drop spindle axle, by using suspension hangers of different heights, or by using “overslung” or “underslung” spring mounts.

What is the difference between a straight spindle and a drop spindle?

As the name implies, a straight spindle, and therefore the center of wheel hub, is in-line with the center of the axle beam. With a drop spindle, the center of the wheel hub is offset from the center of the axle beam.  Drop spindles are most often used for applications that require a lower trailer frame and deck height.

What are the two main measurements required to order a leaf spring axle for a single wheel trailer application?

You must have both the correct hub face and spring center.

What is the correct description for hub face measurement?

Hub face measurement is the distance from the wheel mounting surface on one hub to the wheel mounting surface of the opposite hub.

What is the spring center measurement?

This is the distance from the center of one spring seat to the center of the opposite spring seat.

What is track width and how does it differ in definition from hub face?

Track width is used in dual wheel applications and is the measurement from the middle of the two tires on one side of the axle to the middle of the two tires on the opposite side. Hub face is generally referenced in measuring or referring to single wheel trailer applications.

What is axle overhang and why is it important?

Axle overhang is the difference between the hub face measurement and the spring center measurement. This measurement can best be designated in two ways: each end of the axle or both ends of the axle added together.

This measurement is important and is used to calculate the actual beam strength of the axle, because as the length of the overhang increases, the more stress is placed on the axle beam.

What is the difference between a 60R and a D60 axle?

A 60R axle is rated at 6,000 lb capacity utilizing a light-duty wall axle tube. With the light-duty tube, overhang is limited to 15” when using a straight spindle. 

A D60 axle is rated at 6,000 lb capacity utilizing a medium-duty wall axle tube. With the medium-duty wall tube, overhang can be expanded to 20.” All other components of 60R and D60 axles, including spindle, hub, brake, and bearings, are the same.

What is the primary difference between a 10KGD (general duty) and a 10KHD (heavy duty) axle?

The 10KHD heavy duty axle uses a larger diameter spindle; therefore, the corresponding spindle nuts and spindle washers will be larger. The bearings will also be larger on the 10KHD (395S inner, 387A outer) than on the 10KGD (387A inner, 25580 outer). On a brake axle, the 10KHD also has larger drum brakes (12 ¼” x 4”) than the 10KGD (12 ¼” x 3 3/8”)

Why are axles cambered and what does the word camber mean?

Cambered axles have a slight upward bend in the middle of the axle beam, which is approximately 1° on Dexter axles. As load is applied, the camber in the axle flexes and the tires make full contact with the road.

If the axles you are using are not cambered, you will typically encounter increased tire wear on the inside edge of your tires.

How is axle capacity determined?

All axles have a gross axle weight rating, or GAWR. This term refers to how much weight your axles can carry and is determined by the lowest rated component in the assembly.

There are numerous factors that determine the weight rating on a particular axle, including such items as tube diameter, tube wall thickness, tube length, overhang measurement, bearing combinations, and the type of hub that will be used.


How does the integral suspension system work on a torsion axle?

The axle spindle is mounted to a torsion arm that is permanently attached to a solid machined bar, which is surrounded by rubber cords within the axle beam.  As load is supplied, shock absorption is provided by the solid bar rotating, causing a rolling/compressive resistance in the rubber cords. This rotating action provides a similar functionality as conventional leaf springs.


What is the torsion arm on a Torflex axle?

The torsion arm is the manufacturing method that that enables the axle spindle to be attached to the axle beam. One end of the torsion arm is attached to the solid bar, which slides into the axle beam the other end has the spindle mounted to it. The torsion arm is often called the “dog bone” because of its shape.

What are some advantages of using a torsion axle vs. a spring axle?

Torsion axles have a 5-year manufacturer’s warranty, whereas leaf spring axles have a 2-year manufacturer’s warranty. Rubber cushioning eliminates metal-to-metal contact and there are no suspension parts to wear out. 

Independent suspension on the torsion axle allows for a quieter, smoother ride with less sway. Torsion axles also have multiple starting angles to achieve various trailer heights.




What is the starting angle on a torsion axle?

This is the angle of the torsion bar relative to the horizontal plane (trailer frame). Torflex axles are available in different starting angles, which determine the trailer frame height.


Can the starting angle be changed on a Torflex axle?

No. Because the different starting angles are built using different components, the starting angle cannot be changed once the axle is built.


What are the common starting angles available for torsion axles?

The common angles are 45° down, 22.5° down, 0°, 10° up, and 22.5° up.

0° starting angle: The center of the spindle is on the same horizontal plane as the center of the axle beam.

Up starting angle: The center of the spindle is above the center of the axle beam, which lowers the trailer frame.

Down starting angle: The center of the spindle is below the center of the axle beam, which raises the trailer frame.

Are suspension hangers required to mount a torsion axle to the trailer?

No, hangers are not required on torsion axles. Torsion axles are mounted directly to the trailer frame using brackets that are an integrated part of the axle assembly.

Can I move the mounting brackets or weld additional mounting brackets on a Torflex axle?

No. The mounting bracket is an integral part of the axle assembly and cannot be moved. Because of this, the Outside of Bracket (OB) measurement is required when ordering a Torflex axle. Also, the beam of a Torflex axle should not be welded because the internal rubber cords can be damaged.

What are some of the required specifications that enable you to order the correct Torflex axle?

Hub face (HF) measurement, outside of bracket (OB) measurement, starting angle, and rubber suspension capacity.

What is the hub face measurement?

This is the distance from the wheel mounting surface on one hub to the wheel mounting surface on the opposite hub.

What is the outside of bracket (OB) measurement?

This is the distance from outside of the mounting bracket on one end of the axle to the outside of the mounting bracket on the opposite end of a torsion axle. 

Because torsion axles are mounted directly to the frame, this is same measurement as the outside of the trailer frame where the axle will be mounted.

What is the term top mount as it refers to torsion axles?

This is the method to mount the Torflex axle when the trailer frame is built using “C” channels or “I” beams. The mounting bolts are assembled through the top of the bracket and bottom flange of the frame rail.

What are side mount brackets?

This is an optional mounting bracket that can be used to mount Torflex axles when the trailer frame is built using tubular members. The mounting bolts are assembled through the side of the torsion axle bracket and side mount brackets. The side mount brackets are then welded to the trailer frame.

What is “standard orientation” as the term relates to Torflex axles?

Standard orientation is where the longest vertical surface (leg) of the Torflex mounting bracket is positioned toward the middle of the axle.

What is “reverse orientation” as the term relates to Torflex axles?

This is an optional mounting bracket where the longest vertical surface (leg) of the Torflex mounting bracket is positioned toward the outside of the axle.

Which bracket orientation should I use on my Torflex axle?

It depends on the setup of the trailer frame. The longest vertical surface (leg) of the mounting bracket should be under the vertical segment of the frame member.

Can Torflex axles be used in triple axle applications?

Yes, if using the “T” series of Torflex axles. The “T” series uses a special axle beam and ruggedized components to stand up to the demands of a triple axle application and is available in the #12, #13, and #14 series of Torflex axles.

Are spindles replaceable on Torflex axles?

Yes, if the axle was originally ordered with the replaceable spindle option, which Dexter Axle began offering in early 2014.

Do torsion axles require specials hubs?

No. Torsion axles use the same hubs and hub/drums as comparable leaf spring axles.

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