Suspension question: Control arms versus trailing arms?

Chris

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I've got a question for some of the more knowledgeable suspension guys.

When I watch KOH, I notice a lot of the vehicles have rear trailing arms with the coilover attached to the trailing arms as oppose to the axle itself (like it is on our Jeeps).

What is the reason for this?

Also, in this case, is it called a trailing arm or a control arm, and what's the difference?

Here's a photo of Randy Slawson's KOH buggy. Look at the rear coiler and you'll see what I'm talking about.

randy-slawson-koh-buggy.jpg
 
From my good old days of air cooled dune buggies, I'd call them trailing arms.

I'm not exactly sure why the coilovers are attached to the trailing arms but maybe it's to get actual suspension travel that is longer than the travel available from any coilover. The old VW suspension used the torsion bar which was the actual pivot point of the trailing arms, the shocks were about 3/4 of the way closer to the axles.
 
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@mrblaine or @pcoplin probably knows for sure.

Okay, so they are trailing arms then. I'm curious what constitutes a "trailing arm" versus a "control arm" as well.

I notice that most of the rigs seem to be setup this way, and it got me wondering why exactly this is.
 
Trailing arms are a way to get more suspension travel out of a shorter shock. Shaft speeds on longer shocks get too fast, and it's easier to spring a shorter shock. Long light springs don't tend to last long.

You have to use a larger diameter shock, more valving, and heavier spring rates than an axle mounted shock.

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Also, the same style of arm in the front is referred to a leading arm.

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Good info. Is there a reason so many of these purpose built KOH rigs then use trailing arms and leading arms over a control arm and axle mounted shock / coilover?
 
Yes, they have 20 inch or more rear travel. You do not want a 24 inch travel coilover.

All higher travel desert rigs will have rear trailing arms.

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And the reason for not wanting a 24" travel coilover is due to the faster speeds of the longer shaft, correct?
 
Yes, although they flat-out don't make coilover springs long enough.

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