School me on mid-arm vs long-arm

[Rock Toy]

New guy on this website. I joined because there seems to be quite a bit of info on Savvy Mid-Arms here and I'm curious. I am not buying a kit from anyone. Building my own four link for the rear right now and have some questions about Mid-Arms vs Long Arms. I already have Rokmen short arms and am simply going to get longer link material and reuse the Johnny Joints. Rear axle already has a truss with upper arm mounts on it. So all I am missing is the frame side link mounts.

First obvious question is "what is the difference between mid and long arm"? As far as I can tell, the Savvy Mid-Arm is just a 4 link with slightly shorter arms. Looks like the rear lowers for a TJ are right around 26"-27" long. At what point does a mid-arm turn into a "long-arm"?

Second question is regarding anti-squat. Based on my 4-link calcs, when using the stock axle-side lower link mounts and truss-mounted uppers, the longer the arms, the closer you get to a 100% anti-squat figure. With 27" arms, I am actually coming up with a figure of right around 130% (so many variables involved that 2 people couldn't possibly come up with the same figure). That being said, why choose to use shorter arms? Is it for better clearance in the rocks?

Final question and this is not meant as an insult towards Savvy or anyone else. I have been looking at 4-link frame mount brackets and they are all pretty much the same: Poly, Gen-Right, Barnes, Ballistic, Artec, TMR, etc. Most have adjustment holes for the uppers in order to dial the suspensions in and they all sell for $100 to $400, depending on whether they come pre-welded or as a kit for you to weld. Why don't the Savvy brackets have adjustment holes? Is it simply because the suspension is a "kit" and has been pre-engineered for a specific level of performance that doesn't need to be tweaked? And that being said, would the behavior of the suspension completely change if someone were to stretch their TJ and extend the arms another 4-6"?

Sorry for all the questions. I have searched the Interwebs to exhaustion and simply can't find some of these answers. I appreciate any responses that I might get. I'll be fabbing in the next week or 2 and want to make sure that I do the right thing.

 

[Blackjack]

New guy on this website. I joined because there seems to be quite a bit of info on Savvy Mid-Arms here and I'm curious. I am not buying a kit from anyone. Building my own four link for the rear right now and have some questions about Mid-Arms vs Long Arms. I already have Rokmen short arms and am simply going to get longer link material and reuse the Johnny Joints. Rear axle already has a truss with upper arm mounts on it. So all I am missing is the frame side link mounts.

First obvious question is "what is the difference between mid and long arm"? As far as I can tell, the Savvy Mid-Arm is just a 4 link with slightly shorter arms. Looks like the rear lowers for a TJ are right around 26"-27" long. At what point does a mid-arm turn into a "long-arm"?

Second question is regarding anti-squat. Based on my 4-link calcs, when using the stock axle-side lower link mounts and truss-mounted uppers, the longer the arms, the closer you get to a 100% anti-squat figure. With 27" arms, I am actually coming up with a figure of right around 130% (so many variables involved that 2 people couldn't possibly come up with the same figure). That being said, why choose to use shorter arms? Is it for better clearance in the rocks?

Final question and this is not meant as an insult towards Savvy or anyone else. I have been looking at 4-link frame mount brackets and they are all pretty much the same: Poly, Gen-Right, Barnes, Ballistic, Artec, TMR, etc. Most have adjustment holes for the uppers in order to dial the suspensions in and they all sell for $100 to $400, depending on whether they come pre-welded or as a kit for you to weld. Why don't the Savvy brackets have adjustment holes? Is it simply because the suspension is a "kit" and has been pre-engineered for a specific level of performance that doesn't need to be tweaked? And that being said, would the behavior of the suspension completely change if someone were to stretch their TJ and extend the arms another 4-6"?

Sorry for all the questions. I have searched the Interwebs to exhaustion and simply can't find some of these answers. I appreciate any responses that I might get. I'll be fabbing in the next week or 2 and want to make sure that I do the right thing.

Mid arm is really just a way to distinguish that it is not just another long arm. Savvy has set the arm locations because the kit is based on being at 4 inches of lift height and stock wheelbase so no adjustment is necessary. It also requires a body lift as it is necessary to get the geometry that they wanted to achieve.

The reason for the shorter arm length is packaging. Once you make your arm length on a TJ more that 26ish inches you cannot achieve enough frame side arm separation without extensive modification to the tub. This is the biggest problem with all bolt on long arms and even a large percentage of the semi custom stuff as well. If you look at the Savvy rear uppers they are about as far up as you can go and not have them crash into stuff under the jeep.

If you are want to do anything outside of being 4-4.5 inches of lift height and stock wheelbase the Savvy is not the kit you are looking for.

 

[Chris]

Lots of good info in this thread as well:

https://wranglertjforum.com/threads/currie-short-arm-vs-savvy-mid-arm.30235/

 

[Chris]

I’ll also tag @mrblaine in this, since he is after all the guy who designed the Savvy mid-arm. That being said, he can answer some of these questions I’m sure.

 

[BuildBreakRepeat]

The main point of most material you’ll read on here about “mid-arms” is that arm length is simply a by product of correct geometry. The mid arm was developed for good geometry on climbs and off camber situations, ample clearance when running 35s, and solve specific issues that short arms occasionally show.

 

[toximus]

I'll let you read the thread Chris linked to, lots of good info over there.

The long and short of it is that all arm lengths are a compromise, including the mid-arm, the question you need to answer is which one compromises in areas that you don't want to compromise on? For me, the Savvy mid-arm is the most well balanced and minimal areas are compromised in.

I already have Rokmen short arms and am simply going to get longer link material and reuse the Johnny Joints.

Check that the diameter is up to the task of being longer.

Rear axle already has a truss with upper arm mounts on it. So all I am missing is the frame side link mounts.

There's more to good geometry than having brackets, location and angle need to be considered.

First obvious question is "what is the difference between mid and long arm"?

It's just a term that was coined for easy conversation. Short arm is stock, long arm connects in the belly skid area, mid-arm is half way between.

At what point does a mid-arm turn into a "long-arm"?

The design process behind the mid-arm is that the arms are as long as they need to be and no longer. So I suppose it turns into a long arm when the arms are longer than they need to be and become a compromise more than they do a benefit.

Why don't the Savvy brackets have adjustment holes?

Because the suspension works as is. Nothing needs to be adjusted. There is also no room for adjustment if your build is overall well rounded — adjustable brackets would just get in the way and lead to compromises.

And that being said, would the behavior of the suspension completely change if someone were to stretch their TJ and extend the arms another 4-6"?

There's a little adjustability in the arm length if you need to move things around to package the axle a certain way but for that much stretch you should move the rear frame brackets instead of lengthening the arms.

Building my own four link for the rear right now

What are you trying to gain from changing the length of the arms?

 

[Rock Toy]

I don't have any "intentions" about the length of the arms. Just trying to figure out why they chose that specific length. There are a ton of long arm kits that all claim to be balanced and more then enough short and mid arm kits that claim the same. I guess that I am trying to figure out exactly what is balanced? What are the anti-squat, anti-dive and roll center that are ideal and how do I go about getting to those numbers? I keep hearing folks saying that this system or that system was designed "for correct geometry" or to "solve a problem" but no specifics. I am trying to "understand" what the designers were thinking so I can design my system to work for me.

For example, how would the rear suspension behave differently if the frame mounts were moved 2"s in either direction and why are they placed exactly where they are? How much of that is compromise to make the kit more user-friendly for installation and how much is for the best performance? And is that performance for street manners or rock crawling? I am more than certain that the Savvy system works and would gladly pay for it if I wasn't halfway there with my own parts (or if they sold just the frame-side brackets....hint, hint) but I just want to know if I should copy the geometry or tweak it a little to come up with a better system for me. That's all.

 

[mrblaine]

I’ll also tag @mrblaine in this, since he is after all the guy who designed the Savvy mid-arm. That being said, he can answer some of these questions I’m sure.

This is not a Savvy Mid arm question. This is a suspension question.

 

[mrblaine]

tweak it a little to come up with a better system for me. That's all.

If you could tweak it better, it already would be.

 

[toximus]

I am trying to "understand" what the designers were thinking so I can design my system to work for me.

What doesn't work about your current system?

 

[Rock Toy]

If you could tweak it better, it already would be.

Awesome. You mind sharing with me how you ended up where you did with the arm lengths that you have? More specifically, why not longer? What do you feel you would lose by going with longer arms?

 

[Blackjack]

Awesome. You mind sharing with me how you ended up where you did with the arm lengths that you have? More specifically, why not longer? What do you feel you would lose by going with longer arms?

Make sure to read the other thread. Lots of what you are asking is in there. Some good reads here:

https://wranglertjforum.com/threads/long-arm-lifts-vs-short-arm-lifts.13319/
https://wranglertjforum.com/threads/currie-short-arm-vs-savvy-mid-arm.30235/https://wranglertjforum.com/threads...-octane-a-streetable-adventure-lj-story.9956/

 

[someguysjeep]

Awesome. You mind sharing with me how you ended up where you did with the arm lengths that you have? More specifically, why not longer? What do you feel you would lose by going with longer arms?

refer back to post #2

 

[Brianj5600]

@Rock Toy it is hard to get tech here. Product suggestion is about the closest you will get. There are some people that have spent time and money to develop their package. I fully understand them not giving their hard work away for free.

The main point of most material you’ll read on here about “mid-arms” is that arm length is simply a by product of correct geometry. The mid arm was developed for good geometry on climbs and off camber situations, ample clearance when running 35s, and solve specific issues that short arms occasionally show.

Roll center is something that doesn't get much discussion. I would like to hear your thoughts on roIl centers. When you say "good geometry on climbs and off camber" are you talking about with a track bar or triangulated rear suspension? Jeep West seems to lower the front roll center a bit and raise the rear roll center. Savvy seems to leave the stock locations for the front track bar leaving RC as is and by not using a track bar the rear lowers the RC from a normal 4" lifted track bar.

 

[mrblaine]

@Rock Toy it is hard to get tech here.

It doesn't have to be that way. There's lots of smart folk here. If everyone would quit arguing quite so much in tech discussions and actually have a discussion with an open mind, that would foster much more tech.

 

[Blackjack]

@Rock Toy it is hard to get tech here. Product suggestion is about the closest you will get. There are some people that have spent time and money to develop their package. I fully understand them not giving their hard work away for free.



Roll center is something that doesn't get much discussion. I would like to hear your thoughts on roIl centers. When you say "good geometry on climbs and off camber" are you talking about with a track bar or triangulated rear suspension? Jeep West seems to lower the front roll center a bit and raise the rear roll center. Savvy seems to leave the stock locations for the front track bar leaving RC as is and by not using a track bar the rear lowers the RC from a normal 4" lifted track bar.

There is a good amount of info in several threads including talk about roll centers. Jeep West is following a similar recipe that Nth Degree did in regards to roll centers. He lowers the front because he is adding a drop pitman a lot of the time and raising the axle side of the panhard bar is more difficult compared to lowering the frame side. He also is going with bushings in a double shear mount for strength and allows him to push the axle forward a small amount if he so chooses. The high roll center in the rear does make for more stability off camber but at the expense of adding more bind into the suspension overall.

Savvys approach is all about gaining performance with a minor sacrifice in rear roll center. The front is not changed because they want the axle in the stock location as close as possible and at 4 inches of lift a good panhard bar and steering linkage will perform just fine. As Blaine has mentioned a few times the lower roll center in the rear can be made up for with well tuned outboard mounted shocks and good sway bars. This allows less bind in the rear suspension and predictable manners in certain climbs where "jacking" may occur.

You also need to look at where Dave and Blaine wheel at a lot and that will also help understand their approaches. If you spend any time in the Tillamook area of OR you will understand a lot of what Dave does. Tractionless and off camber is the name of the game. Blaine spends a lot of time in JV and has a lot more short vertical climbs and sharp ledges to negotiate. Neither approach is wrong, they are just different solutions to a particular set of criteria.

 

[Jerry Bransford]

You also need to look at where Dave and Blaine wheel at a lot and that will also help understand their approaches. If you spend any time in the Tillamook area of OR you will understand a lot of what Dave does. Tractionless and off camber is the name of the game. Blaine spends a lot of time in JV and has a lot more short vertical climbs and sharp ledges to negotiate. Neither approach is wrong, they are just different solutions to a particular set of criteria.

I doubt Oregon has more off-camber trails than we do out in our SoCal desert trails. The first one is of my previous TJ, the second one was taken in JV of a TJ that Blaine built.

 

[mrblaine]

There is a good amount of info in several threads including talk about roll centers. Jeep West is following a similar recipe that Nth Degree did in regards to roll centers. He lowers the front because he is adding a drop pitman a lot of the time and raising the axle side of the panhard bar is more difficult compared to lowering the frame side. He also is going with bushings in a double shear mount for strength and allows him to push the axle forward a small amount if he so chooses. The high roll center in the rear does make for more stability off camber but at the expense of adding more bind into the suspension overall.

Savvys approach is all about gaining performance with a minor sacrifice in rear roll center. The front is not changed because they want the axle in the stock location as close as possible and at 4 inches of lift a good panhard bar and steering linkage will perform just fine. As Blaine has mentioned a few times the lower roll center in the rear can be made up for with well tuned outboard mounted shocks and good sway bars. This allows less bind in the rear suspension and predictable manners in certain climbs where "jacking" may occur.

You also need to look at where Dave and Blaine wheel at a lot and that will also help understand their approaches. If you spend any time in the Tillamook area of OR you will understand a lot of what Dave does. Tractionless and off camber is the name of the game. Blaine spends a lot of time in JV and has a lot more short vertical climbs and sharp ledges to negotiate. Neither approach is wrong, they are just different solutions to a particular set of criteria.

That is all very correct except for one minor thing. This is very common in JV-

We absolutely need off camber stability out there.

 

[Rock Toy]

It doesn't have to be that way. There's lots of smart folk here. If everyone would quit arguing quite so much in tech discussions and actually have a discussion with an open mind, that would foster much more tech.

That's always the case in these Bulletin Boards. So that being said, how would you suspension change if the arms were longer? I have read through all of the discussions recommended and haven't found the answer to my question. I suppose that it really doesn't matter because I'll end up doing what I do based on my research but I really do like Savvy products and engineering and if there is something there that has already been figured out, I would love to know what it is.

 

[mrblaine]

That's always the case in these Bulletin Boards. So that being said, how would you suspension change if the arms were longer? I have read through all of the discussions recommended and haven't found the answer to my question. I suppose that it really doesn't matter because I'll end up doing what I do based on my research but I really do like Savvy products and engineering and if there is something there that has already been figured out, I would love to know what it is.

What do longer arms do for you? You are coming at it from the direction that one needs a longer arm equivalent to the length commonly used on a long arm kit. Why do you think you need an arm that long?