AEV JK suspension testing photo from today!

[Cole]

Hey Dave.....STALKER!!!:coffeedrink:

 

[winkosmosis]

No. Jim had some pretty compelling points about why the JK does not need and can't use a long arm.

First was the concept that the TJ has smaller fender openings and needs much more lift to fit the same size tires. That combined with it's short arms made it really benefit from long arm kits.

The JK on the other had requires about 1/2 as much lift (or less) to fit the same size tires and comes with much longer arms and better mounting locations stock. Jim Frens said the only way to do a long arm correctly on a JK would be to remove the gas tank. Mounting to the outside of the frame rail negates the advantages of the long arm. (I'm not exactly sure why, but he is the engineer).

Too many companies simply applying what sold on the TJ to the JK without the proper engineering behind it.

But 4.5" is a pretty big lift. So in this case, it's a big lift, not a small lift taking advantage of the big wheel wells. Are the JK control arms longer so the angle isn't as severe?

Here is the Procomp setup

4WD magazine likes it http://www.4wdandsportutility.com/features/jeep/0805_4wd_pro_comp_jeep_jk_kit/index.html

 

[Zeero]

No. Jim had some pretty compelling points about why the JK does not need and can't use a long arm.

First was the concept that the TJ has smaller fender openings and needs much more lift to fit the same size tires. That combined with it's short arms made it really benefit from long arm kits.

The JK on the other had requires about 1/2 as much lift (or less) to fit the same size tires and comes with much longer arms and better mounting locations stock. Jim Frens said the only way to do a long arm correctly on a JK would be to remove the gas tank. Mounting to the outside of the frame rail negates the advantages of the long arm. (I'm not exactly sure why, but he is the engineer).

Too many companies simply applying what sold on the TJ to the JK without the proper engineering behind it.

Some excellent points that I am total agreement with. The JK is a different machine from the TJ, and you have to do the mods intelligently.

 

[Cole]

But 4.5" is a pretty big lift. So in this case, it's a big lift, not a small lift taking advantage of the big wheel wells. Are the JK control arms longer so the angle isn't as severe?

Here is the Procomp setup


4WD magazine likes it http://www.4wdandsportutility.com/features/jeep/0805_4wd_pro_comp_jeep_jk_kit/index.html

I have talked to the ProComp guys in depth (and FWIW with a couple of the 4wd guys present). It should be noted that the Procomp is a 6" lift.

I did not get to drive the Pro Comp lift so can't comment on that.

One thing that keeps bothering me is that all these long arm kits sacrifice ground clearance. From what I have learned I wonder how much a long arm is needed, or is it more of a sales gimick at this point?

 

[Cole]

Youtube video of the trip. Ran it all unlocked. My Jeep starts at 2:24


http://www.youtube.com/watch?v=-YXE...showthread.php?t=9907&feature=player_embedded

 

[Zeero]

One thing that keeps bothering me is that all these long arm kits sacrifice ground clearance. From what I have learned I wonder how much a long arm is needed, or is it more of a sales gimick at this point?

I'd be leaning towards the whole "Gimmick" thing, it certainly is a "Badge of pride" for alot of owners, but I don't think its a functionally effective piece of equipment.

 

[Cole]

On a TJ you NEEDED some sort of control arm correction when gaining the height required for big tires.

Not really sure it is needed on a JK.

For example. A typical TJ runs 2.5" of lift to fit 32" tires. At this height the control arms are already starting to slope. A JK comes stock with 32" tires and the LONGER control arms are running flat at this height.

You only really need about 2.5-3" of lift on a JK to run 35s. At this height with the longer stock arms there is still less angle change than a TJ running 32s. I would guess that a JK on 4.5" lift has about the same control arm angle as a TJ on 2" of lift. (guess, but would be curious to measure it).

 

[winkosmosis]

TJ LCA length is 18.75" vs 22.5" for the JK, so 20% longer. So to me that still means 4.5" on a JK is enough to warrant longarms.

 

[Root Moose]

It's all about the angles of the arms.

If the amount of lift added makes the front arms point into the frame rails the ride will be affected for the worse. Small lifts and small angle changes will cause little noticeable change in ride quality.

If you have a substantial angle to the arms and want to deal with this then the arms either need to be reconfigured so that they are parallel to the ground again (drop brackets) or the entire configuration needs to be changed.

Long arms fall into the realm of complete and total reconfiguration. Don't knock it until you understand what the geometry is doing with respect to anti-dive, anti-lift and axle location. Additionally, the longer the arms the less caster change and possibly variation in roll steer as the the suspension cycles through its motion.

A well designed long arm suspension is hardly a gimmick. If it was you wouldn't see it used on Jeep Speed competition vehicles. Or other classes of racing, including rock racing or KOH. There would be no need.

I've never been very impressed with anything put out by ProComp. The image above does not change that opinion.

$0.02

 

[Root Moose]

I would guess that a JK on 4.5" lift has about the same control arm angle as a TJ on 2" of lift. (guess, but would be curious to measure it).

If that is the case then I would agree that there would probably not be that much advantage to running a long arm system on a JK.

It would only be worth the bother to add a long arm system if you really needed the extreme articulation for some reason or were very anal about ride quality.

In the case of articulation, normal length arms on Jeep suspensions seem to work quite well after having some tuning done to them.

$0.02

 

[winkosmosis]

The 20% extra length means you can have 20% more lift with the same resulting control arm angle. So instead of 2.5", you could go to 3" but 4.5" is a lot more

 

[Cole]

The 20% extra length means you can have 20% more lift with the same resulting control arm angle. So instead of 2.5", you could go to 3" but 4.5" is a lot more

My trigonometry is a bit rusty here, but I do know that it is not quiet a direct calculation like that.


Someone correct the math if I forgot something here.

A 2.5" lift on a 18.75" arm is about a 7.6*(degree) change.
Same lift on a 22.5" arm is about a 6.2* change.

A 4.5" lift on the TJ gets it up to 13.6*
The JK about 11.4*

Now to put this in perspective. To fit 35s at full stuff with suspension lift alone on a TJ you need about 5-6" of lift. Which puts the control arms at about 18*. On a JK you need 2.5-3" of lift. Which is a 7.6*.

Meaning that to run the same size tire the TJ control arm angles change by more than 10* more than a JK does.

Most people don't long arm a TJ until you pass 4" of lift, and you can see that on the JK it would take you 7.5" of lift to equal the steep control arms angle of a TJ with 4' of lift.

 

[Aggie]

Ok Cole, I have been thinking about the 4.5" AEV kit for quite a while now. We know it performs great On-Road, we have seen that. This is the reason I am seriously considering it. I have seen the videos of you driving it over some simple trail riding which is where I would be doing most of my off roading. Have you had a chance to truly flex it out? How stable did the truck feel as you were going over the rocks?

 

[winkosmosis]

On a TJ you NEEDED some sort of control arm correction when gaining the height required for big tires.

Not really sure it is needed on a JK.

For example. A typical TJ runs 2.5" of lift to fit 32" tires. At this height the control arms are already starting to slope. A JK comes stock with 32" tires and the LONGER control arms are running flat at this height.

You only really need about 2.5-3" of lift on a JK to run 35s. At this height with the longer stock arms there is still less angle change than a TJ running 32s. I would guess that a JK on 4.5" lift has about the same control arm angle as a TJ on 2" of lift. (guess, but would be curious to measure it).

You don't have to do all that math and angle figuring. Assuming the arms start horizontal, you have a right triangle as you lift. For a given LCA angle, you have a 20% longer arm, therefore 20% taller lift.

 

[Cole]

Your math is wrong. The length of the control arm and the lift height can't change as a direct percentge