Redneck Trailer Supplies

RTS 101: Suspensions

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

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What is a trailer suspension?

This is a method for absorbing road shock, cushioning cargo, and attaching axles to the trailer frame using a torsion axle, leaf spring system, or air suspension system.

What are the two types of leaf springs and how are they different?

(1) Double eye, which have eyes formed in both ends of the spring 

(2) Slipper, which have an eye formed in one end and a curved surface on the rear end

Slipper springs are generally used in heavier applications and come in more sizes and higher-rated capacities.

What is the proper method to mount leaf springs to the axle?

Use two properly sized U-bolts on each side of the spring that sandwich the spring between a properly sized axle plate and the spring seat on the axle. Springs can be mounted either overslung or underslung.

How do I determine the proper replacement U-bolts for an axle?

U-bolts come in multiple diameters, lengths, and different bends based on the diameter of the axle beam, capacity of the axle, and shape of the beam. 

The best way to select the proper replacement U-bolt is to measure the old U-bolt. If this is not available, then the U-bolt section of the Redneck catalog will provide a starting point.

How do I determine the correct replacement leaf spring?

1. Determine the type of spring (double eye or slipper). 

2. Measure the width, length, and arch of the spring.  

3. Count the number of leaves.  

4. Determine the weight capacity of the axle. (Keep in mind that a used/worn spring can be longer and the arch shorter than the correct new spring replacement).

If an axle is rated at 3,500 lbs. what is the minimum rated capacity of the springs that should be used?
To maintain the full rated capacity of the 3,500 lbs., the leaf springs should have a minimum rated capacity of 1,750 lbs.

Where are shackle straps used on a suspension?

Shackle straps are used to connect one end of a double eye spring to either a hanger or equalizer.

When are equalizers used in a trailer suspension?

Equalizers are a suspension component that is used on multi-axle applications that allow transfer, or equalization, of a portion of the load on one axle to an adjacent axle(s) when traversing an uneven surface.

How many hangers are used on a trailer?

It depends on the number of axles on the trailer: 

Single axles (2 front and 2 rear)

Tandem axle (2 front, 2 center, and 2 rear)

Triple axle (2 front, 4 center, and 2 rear)

What information is required to order a replacement hanger?

Type of spring (slipper or double eye)

Width of the spring

Capacity of the axle

Location of the hanger

Height of the hanger (measured from the top of the hanger to the center of the bolt hole)

Bolt size

What is static bump clearance and why should I be concerned about it?

Static bump clearance is the measurement from the top of the axle to the bottom of the trailer frame in a full load situation. 

If this is greater than 2.5”, a bump stop should be used to avoid overstressing the leaf springs. 

If it is less than 1.5”, full suspension movement may be limited and result in damage to the frame and/or axle(s) when operating on rough or uneven road surfaces.

Do leaf springs have a front and back?

On slipper springs the eye of the spring goes to the front of the trailer. On double eye springs the spring clips go to the front of the trailer.