Tuesday Tech Tip #3 - Extended Radius Arms

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There are a couple of reasons to extend your radius arms:

1. Your lift is so high that corrective C bushings can no longer compensate for the change in caster (see last weeks Tech Tip)
2. You need more suspension articulation, the longer radius arm puts more leverage on the springs, allowing for more travel


There are a few things to think about when building or buying extended radius arms:

• Is it important to increase the positive caster?

Almost all lifted Broncos need some correction of caster. You may be able to get enough correction from C bushings (again, see last weeks tech tip)

• Do I want to use a heim style joint or the stock type with a bushing?

Tough call, many will tell you there is no difference in ride quality, but I can't believe that having a rubber or poly bushing on the end of the radius arm doesn't help absorb some of the road bumps.

• How long?

The length is a tough issue to settle, many of the manufactured arms are 10-12" longer than stock. Some of the home-made units I have seen vary between 6" and 14" longer than stock. 

• How much bend to correct the angle of the radius arms?

Stock radius arms are angled inwards, this is because the radius arm mounting surface on the axle is wider than on the frame (the springs sit on top of of the radius arms, which sit outside the frame). This graphic below will help explain. The angle is approximately 15 degrees, the dotted line shows where an extended radius arm would need to mount if we do not correct the angle. In addition if we make the correction where the tires might hit the radius arm, we can benefit from tighter turning when running wide tires.

 Options:


James Duff makes them with 2" O.D., .313" wall DOM tubing and 1/4" steel plate. Theirs are made from 100% new components. They are 10.75" longer than stock and have 4.75 degrees of caster built in. Their design makes them sit up higher for added ground clearance and the angle correction provides more tire clearance.

Cage Off-Road made some identical to the James Duff units, there is a reason for that, the same person designed both sets. I don't think these are available anymore.

These extended arms are built by the folks at All For Fun Off-Road
These units also have a slight correction in the angle. They use the stock style bushing and mount.

 
These "Lars Bars" were crafted by a mechanical engineer at his home, made from 2" O.D. , .250" wall DOM tubing, some joints and some original donor radius arms, they are 6" longer than stock and feature a 9 degree bend at the end.

Here are a bunch of Home built units