Different long-arm question

[jjvw]

Thanks for that, this is complicated stuff but I find it very interesting, it's been like peeling back the layers of an onion gradually learning about the TJ suspension system.

When designing suspension geometry for a rock crawler, is the goal always one of those three options (extend vs compress vs neutral)? What i mean by that is whether it would always be desired for a neutral reaction for example?

During a steep climb, lifted short arms result in the rear lifting until traction is lost and the whole thing collapses, then starts again. This is the hopping we see.

Long arms all put the rear frame side control arms mounts in about the same place to allow for a simpler bolt-on kit. This fixes the hopping while making the rear sink during a steep climb. The result is the front end getting light due to the weight transfer. The Jeep wants to do a backwards somersault.

The Savvy midarm does not hop and it does not sink during a steep climb. The behavior of the suspension is calm and predictable. The difference is where the control arm mounting positions are located. This is why the midarm is not a bolt-on kit.

 

[inkedrose]

Thanks for that, this is complicated stuff but I find it very interesting, it's been like peeling back the layers of an onion gradually learning about the TJ suspension system.

I'm a visual person, @jjvw literally had to draw this out for me to understand

 

[jjvw]

I'm a visual person, @jjvw literally had to draw this out for me to understand

Instant center and antisquat are both very thoroughly discussed topics in suspension design with many better diagrams than what I made on the whiteboard. The moment one can understand how those two things interact, it all gets a lot easier to figure out. After that, realizing that these behaviors only really matter to us in very specific circumstances makes you understand why long arm marketing is a pile of lies and that the calculators are largely useless because they all assume static loads on flat ground.

Hard braking and how the front sinks from weight transfer is also affected by instant centers and antisquat from the front suspension with the forces going the opposite direction.

A very interesting dynamic involving instant centers and antisquat is where it relates to hard cornering with independent suspension. The same behaviors of a raising and sinking suspension while under load will affect how the outside tire will push into the ground and provide traction through weight transfer.

After all of that, then realize how important shocks are for controlling movements and you can begin to understand why getting good shocks fitted should take priority over changing control arm mounting positions.

 

[JMT]

long arm calling

And what would that calling sound like?

 

[GregBelleville]

I'm a visual person, @jjvw literally had to draw this out for me to understand

Same, I definitely don't understand instant center, anti squat, etc. but I understand what jj is saying about why the neutral handling rear prevents the short comings of both the short arm (axle hop) and the long arm (light front end).

 

[UhOh]

Like @inkedrose, I am also one of the few running a long arm TJ. Specifically a Teraflex LCG Enduro with the Falcon shocks appropriate for it. I had it installed when I was pretty new to all this, thinking that the longer arm would give me more capability. I've been happy with the setup as I've progressed in my wheeling. Certainly I have learned quite a bit more over time, still, for the intended future uses of my TJ I am comfortable with the setup. I have experienced the limitations of the long arm, especially the light front end on steep climbs which to me is also a function of the short wheelbase of the TJ.

All that being said, I did install the midarm on my LJ

 

[mrblaine]

I have experienced the limitations of the long arm, especially the light front end on steep climbs which to me is also a function of the short wheelbase of the TJ.

Put another way, the short wheelbase needs all the help it can get so it makes little sense to make that worse with a long arm.

 

[UhOh]

Put another way, the short wheelbase needs all the help it can get so it makes little sense to make that worse with a long arm.

For sure.
I keep learning!

 

[inkedrose]

And what would that calling sound like?

it's a very loud "cha ching"

 

[PurpleTJAZ]

Apparently my education is lacking. I thought the choices were stock or long. Guess I need to read up on this “mid” thing.

If you want to see a Mid-arm in the wild, let me know and we can meet up.

 

[any4xx]

If you want to see a Mid-arm in the wild, let me know and we can meet up.

Absolutely! I’m in Vail just South of TUS.