Long Arm Lifts vs. Short Arm Lifts

[jjvw]

I figured if the control arms were extended and new mounts were welded on the frame to support the longer control arms, that would bring that instant center line down, closer to the purple antisquat line. Or in my mind, it looks like if you extended the wheelbase enough, you'd eventually bring the instant center down further.

It seems to me that the further up you go with the lift, the more of an angle you have with the control arms. That instant center line is relative to the angle of the control arm angle (from the way I'm looking at those images at least), so this is where I'm getting my thought process from.

Let's keep things a little simple. The moment we start extending the wheelbase, we are in a whole different type of build.

Moving mounts is the correct approach. What happens if you were to flatten the arms? What happens if you make them more parallel to each other?

 

[Chris]

Let's keep things a little simple. The moment we start extending the wheelbase, we are in a whole different type of build.

What happens if you were to flatten the arms? What happens if you make them more parallel to each other?

I see what you're saying... if you make the arms flatter and more parallel with each other, you should at some point achieve the desired result... I think (if I had that software to play around with I'm sure I could either prove or disprove this).

But the reason that doesn't make much sense to me, is because how do we make the control arms more parallel (and flatter) to each other without making them hang down lower (maybe that's the wrong way to describe it)?

 

[Chris]

Maybe I'm wrong... when I look at this photo of mid-arms, I can clearly see they are much more parallel to each other. But of course, it seems this was in part achieved by extending the length of the arm and moving the mounting locations around both on the frame and axle.

 

[jjvw]

They are more parallel. This is accomplished by raising the upper axle side mount a bit, along with the upper frame side mount. This is the vertical separation between the upper and lower mounts that comes up so often in these examples. Additionally, moving the frame mounts away from the axle will flatten the arms and make them longer.

This combination of adjusting the vertical separation and lengthening the arms will move the instant center down and further away. This is what we want in order to achieve a lower antisquat number.

The mounts are located where they need to be in order to place the instant center in a certain location. The arm lengths are largely the result is connecting the mounts together. What really matters are the mount locations, not the arm length.

Here is what mine looks like as it sits in the garage tonight. The instant center is lower and projected further out. The antisquat is in the high 80s.

 

[Chris]

By raising the upper axle side mount a bit, along with the upper frame side mount. This is the vertical separation between the upper and lower mounts that comes up so often in these examples. Here is what mine looks like as it sits in the garage tonight. The instant center is lower and projected further out. The antisquat is in the high 80s.
View attachment 53481

This is what I figured. I hadn't really paid much attention to how those mid-arm lifts were attached, but I went just a moment ago to the Savvy site (and a Google search) to see how they have them mounted, and it's apparent that the brackets themselves make a big difference in terms of changing the suspension geometry.

I'm so used to looking at the stock control arm mounting brackets that I had no idea how much different the mid arm brackets looked in terms of where they are placed and how they are raised.

So there's more here at work than just control arm length, it's how the control arm brackets are designed and positioned.

I guess this is starting to make sense. I have seen some of these guys off-road who just have this horrible, horrible squat in the rear end when they are wheeling. I'm not talking about sagging springs either, I'm talking about that squat they get when they give it throttle and end up powering up a large embankment or something. The ass end just drops almost entirely.

 

[jjvw]

....

So there's more here at work than just control arm length, it's how the control arm brackets are designed and positioned.

I guess this is starting to make sense. I have seen some of these guys off-road who just have this horrible, horrible squat in the rear end when they are wheeling. I'm not talking about sagging springs either, I'm talking about that squat they get when they give it throttle and end up powering up a large embankment or something. The ass end just drops almost entirely.

I'm not sure what your seeing, but the purpose here is to induce some squat when the tires are producing traction in order to prevent the hopping.

That is part of what will create a smooth climb over a difficult obstacle.

 

[Chris]

I'm not sure what your seeing, but the purpose here is to induce some squat in order to prevent the hopping.

Maybe I am just seeing worn out rear ends then?

The hopping though, does that typically only happen when you're getting heavy on the throttle? I've seen it before, just never experienced it personally.

 

[jjvw]

The hopping occurs when the tires grab and raise the suspension, then they lose traction and the suspension unloads and drops, the tires grab again and raise the suspension, ... Then an axle shaft breaks.

By keeping the instant center low and far away, this hopping won't happen because the Jeep isn't trying to push itself off of the rock face.

Stock TJs don't hop. The higher you lift them, the more they begin hop. This becomes the most pronounced on steep climbs. The true purpose of longer arms (if correctly executed) is to make the Jeep behave more like it did when it was stock.

If you are experiencing this hop on short arms, a bolt on long arm kit will not fix it. The only thing you have achieved is a loss of clearance.

 

[tworley]

jjvw and I spoke briefly about this last weekend when on a tough trail. Its very interesting to see in the real world how two jeeps react to an obstacle differently.

Ive read thru the information posted but am still sipping on my coffee. I need to go back and read this again, but it is very good info.

Ill suggest a sticky...

 

[jjvw]

jjvw and I spoke briefly about this last weekend when on a tough trail. Its very interesting to see in the real world how two jeeps react to an obstacle differently.

Ive read thru the information posted but am still sipping on my coffee. I need to go back and read this again, but it is very good info.

Ill suggest a sticky...

French Creek was one of the spots where we saw the hopping start to happen. A steeper climb, with questionable traction.

On Eagle Rock, I remember watching an LJ with a Teraflex long arm bouncing and oscillating where everyone else just rolled up and over.

 

[bobthetj03]

On a typical off the shelf long arm kit, you are moving the frame mounts as well as using longer arms, but it's not enough to produce a good instant center and antisquat #'s the way I'm understanding all this suspension voodoo.

 

[Mike_H]

Interesting...Are you using the 4-link calculator on Pirate @jjvw ?

I'm paying attention to the hopping discussion. I ran into that on some sandy hill climbs a couple weeks ago. Same physics at play, or something different because of wheelspin?

 

[jjvw]

On a typical off the shelf long arm kit, you are moving the frame mounts as well as using longer arms, but it's not enough to produce a good instant center and antisquat #'s the way I'm understanding all this suspension voodoo.

The mounts are in the wrong locations. They don't put the instant center in an optimal position.

 

[bobthetj03]

The mounts are in the wrong locations. They don't put the instant center in an optimal position.

That is what I mean.

 

[jjvw]

Interesting...Are you using the 4-link calculator on Pirate ? ...
...

Those models are from the 4 link calculator. Some time should be spent discussing it. The calculator is flawed in that it only shows these forces on flat ground. In reality, the instant center changes with the suspension travel. The antisquat line also shifts as the suspension travels and as the vehicle tips, rolls and moves around. Because it is partly determined by the center of gravity, the antisquat line even changes with added cargo, passengers or an empty tank of gas. What actually happens on the road and on the trail is quite a bit different from what is shown in the calculator. We do run the risk of fixating too much on the lengths and measurements we see on the screen rather than trying to understand the overall concepts.

What is important (and where this matters for the vast majority of us) is to understand that these forces exist, they have real world implications on our modified Jeeps, and that they can be manipulated if you have the resources and know what to do. Most of us do not have the resources or know-how to build and refine our own custom suspension, so we must rely on kits. What sets the Savvy kit apart from all other "longer arm" kits is that it was specially designed with these suspension dynamics in mind.

....

I'm paying attention to the hopping discussion. I ran into that on some sandy hill climbs a couple weeks ago. Same physics at play, or something different because of wheelspin?

As I understand it, the hopping tends to occur when when the control arm geometry allows the traction from the wheels to lift the Jeep up. Think of it as repeatedly jumping and slipping while trying to power over an obstacle.

 

[JeepNWilly]

This post has turned into a great information source. :thumbup: It should definitely be a sticky. I have the ability and tools to fabricate but I never built my own lift because my TJ is my daily driver thus I need it for transportation. At some point in the future it will retire from daily driver duties and that is when the custom build will begin.

 

[jjvw]

Hopefully all of this helps shed some light on why so many of us don't encourage using the bolt on long arm kits. Unfortunately, they don't accomplish anything that outweighs the problems they create. A short arm lift, while not perfect, has far fewer compromises.

This entire topic should also be put into perspective. The geometry that we are talking about is only something that presents itself on larger builds. Even then it only becomes an issue in specific instances on difficult trails. I'll be the first to say that my Jeep with mid arms is not being challenged in ways where it's improved geometry is making any difference. I am still the biggest limitation.

As I mentioned earlier, if you don't know why you want longer arms, you probably don't need them. If your Jeep is not up to the more difficult trails, there are far more valuable areas to focus on before you start trying to improve the suspension geometry. Keep your short arms. Don't fall for the marketing!

 

[JeepNWilly]

@jjvw I agree which is why I like this discussion. Most lift discussions become a bashing discussion without any real data. A lot of us don't have the means to spend the $$$ on a Savvy setup so we get what we can while keeping our bill paid. In my case I got the complete RC 6" long arm for under $700 because I was involved with a dealer back then.

 

[Shane Mckinley]

So with the correct understanding and software or maybe eyes to see on trails (if you’ve reached that point in wheeling)

Could it not be achieved solely on mount positions of the longer arms at the frame, axles, and/or skid plate?

Hypothetically because I doubt I’ll ever get into a situation where it’s needed


Sent from my iPhone using Tapatalk
2005 RHD TJ Sport
2010 BMW 528xi

 

[jjvw]

So with the correct understanding and software or maybe eyes to see on trails (if you’ve reached that point in wheeling)

Could it not be achieved solely on mount positions of the longer arms at the frame, axles, and/or skid plate?

Hypothetically because I doubt I’ll ever get into a situation where it’s needed


Sent from my iPhone using Tapatalk
2005 RHD TJ Sport
2010 BMW 528xi

If that were possible, we would have it already. This debate goes back many years. And the "mid arm" concept has been in use on TJs since the earliest days of people modifying them. The Savvy kit has its origins in the suspensions that Currie was building for it's competition rock crawlers. People have known how to build a good TJ suspension for a long time.

The problem is packaging, along with ease of installation. There isn't a lot of room to squeeze the mounts and the arms into the same space as the exhaust and drive shaft. Even if a bolt on kit could find the room to put the mounts in better locations, the bracketry would be bulky, complicated, and weak. Welding to the frame is the only decent solution.