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Making Off Road Trailing Arms

Posted in How To on April 1, 2010
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Trailing arms (AKA lower links) are one of the most important suspension system components on a long-travel linked rear suspension. Trailing arms must withstand forces from three sources: the terrain acting upon the wheels, the weight of the chassis, and the shocks' damping. If your trailing arms aren't strong enough they'll bend, or worse, break.

There are four main factors to consider when designing trailing arms: length, geometry, strength, and ground clearance. Bigger, longer trucks will best use bigger, longer trailing arms. Geometry refers to the lateral (or fore and aft) location of the shock mounts between the front and rear mounting points, and the vertical location of the shock mounts relative to the plane (or centerline) between the front and rear trailing arm mounts. As to strength, more is better, but there's a fine line between weight and strength. Too much strength is almost never a bad thing, but too much weight creates problems. Finally, trailing arms hang down pretty low, so they should be designed with as much ground clearance as possible.

There are three ways to get a set of trailing arms: the super-hard way, the hard way, and the easy way. The super-hard way is to design and fabricate your trailing arms completely from scratch. The hard way is to use pre-cut, pre-designed materials and do the welding and assembly yourself. The easy way is to buy your trailing arms pre-made.

We'll cover the hard way and the easy way in this story.

The Hard Way
This set of trailing arms was designed by my friend Dan Barcroft, who has also designed an online four-link calculator that can be used by anyone to design a complete four-link system. The four-link calculator will help you figure out the geometry of your four-link, but it will not design the individual parts and pieces. Dan designed the trailing arms seen here using Solidworks software, the results of which were sent to Elite Laser Cutting. Elite turned Dan's .dxf files into finely-cut pieces of 4130 Chromoly plate. The assembly and welding were done in a home garage by yours truly.

You're looking at the benefits of our day and age. The old way would have involved paper templates and a bandsaw, which is still a viable, albeit time-consuming, way to fabricate parts. Computer design work and CNC laser cutting streamlined the process. Both 0.125-inch and 0.090-inch sheet thicknesses were used to make these parts. Any thermal cutting process (laser, plasma, oxy-acetylene torch) leaves behind a burned edge (or "scale") that should be removed for optimal weld quality. I sanded the scale away before starting to weld. These trailing arms are 60 inches long and designed to use with a 125-inch wheelbase.
PhotosView Slideshow
PhotosView Slideshow
PhotosView Slideshow
PhotosView Slideshow

The Easy Way
To spotlight the easy way, we headed over to Blitzkrieg Motorsports in Anaheim, California. Blitzkrieg offers its trailing arms in 55- and 60-inch lengths. Forty eight-inch-long trailing arms will be available soon. "We recommend the 60-inch arms for fullsize trucks with a tube chassis," Blitzkrieg owner Nate Hanson told us. "If you're building a fullsize truck with a factory frame, the 55-inch lower arms will create better upper link geometry that's easier on the Heims. A factory frame sits narrower than the outer edges of a tube chassis, and shorter upper links are easier to set up for more triangulation. Greater triangulation means less stress on the Heims, so they last longer. The 48-inch trailing arms are a better choice for smaller trucks with shorter wheelbases."

PhotosView Slideshow

Sources

Blitzkrieg Motosports
Anaheim, CA 92806
714-630-0630
http://www.blitzkriegoffroad.com/
Dan Barcroft's Four Link Calculator
unknown, AK
http://mysite.verizon.net/triaged/4linkcalcv15html/index.html
Elite Laser Cutting
Santa Ana, CA 92705
714-667-1950
http://www.elitelaser.net/
HM Engineering
Fountain Valley, CA 92708
714-979-6631
http://www.hmengineering.netfirms.com/

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