School me on mid-arm vs long-arm

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.

You cannot get the link separation desired at the frame with longer links without modifying the tub or having lower links that hang down too far. Lower link separation does not allow for the best control of the instant center especially when your center of gravity starts moving like in a climb. If the link separation is too low then you might as well run a radius arm. The net effect is the same.

Well seeing as folks are just responding with pictures and not data/words, what's the difference? A picture of a stuck jeep tells me nothing. A picture of a jeep that is not stuck tells me the same. Not trying to be a dick here but we are on page two and nobody has responded to a single question that I have asked :rolleyes:. Now I already know that Savvy is the best and that long arms suck but I can't find out what everyone considers a "long-arm" and why a 27" rear LCA is the best.

Did you go read the other threads I put links to? Typically when "long arm" is being mentioned it is referring to bolt on kits like RE, Tera, Skyjacker and the like. Bolt on kits are about ease of install first and good suspension geometry second. The common trait is that the lower arms usually hover around the 3 foot mark because that is what the Warn XCL used and people just considered that the standard. Ironically Warn had a "long arm" developed for the rear of a TJ that only used what we now call a mid arm. Warn sold the Black Diamond line off before the kit made it out of prototype.

Short arms and tall tires don't work well together. Your starting point is a pretty vertical upper and lower control arm that wants to wants to fight obstacles instead of riding over them. And on the road.....well, a rough ride. But I'm not researching front suspensions at the moment. I am looking for answers about the rear suspension and most specifically, about why Savvy designed the length of their arms at around 27"s. I am NOT attacking them and I am not pretending to know more that you or anyone else on here. Just answer some of my questions. Or don't. But whatever you do, please don't answer my questions with more questions. Seems to be a thing around here..

Unless you are running more than 4-4.5 inches of lift control arm angles have little to do with ride quality. Springs and shocks do.

Savvy put the arms at the length they are because it gave them the amount of link separation, roll center and instant center they wanted. Not moving the lower arm mount on the axle was part of those considerations.

I am actually coming at it from a different direction altogether. I am working the 4-link calculator and trying to get the anti-squat to be as close to 100% as possible. I know that this is a single metric and perhaps not the holy grail but I am focused on it the most because it appears to be the metric that I can change the easiest. That being said, my axle mounting points are fixed. I have committed myself to 37" tires and I have 4.5" springs. The CG Height is what it is (assuming around 34" for my TJ) and that leaves placement of the frame side mounts as the only variables. So the longer the arms, the closer I get to 100%. Shorter arms yield me a higher percentage. So in a nutshell, that's why I'm advocating for longer arms. But I'm definitely not a suspension expert and am trying to get an answer as to why I might prefer a shorter arm. For example, I could see that have shorter lowers keeps the links out of the rocks and shorter uppers might triangulate the axle a little better and prevent it from wandering at higher speeds?

Why the fixation of 100 percent? How much higher of a percentage if the links are shorter? Where is your instant center location? Since you say your axle points are fixed is the link separation at least 9.25 inches? Did you move the lower control arm mount on the axle from the stock location and if you did is it above the axle center line? Too many people fixate on antisquat and keep forgetting that there certain rules that need to be adhered to and that in the end packaging is everything. Stuff is going to go where stuff is going to go.
 
Welcome to my world. Questions are answered with questions.



In the last year I have looked through many many pictures on the Jeep West FB page trying to focusing on the TJ stuff. I noticed a dropped pitman arm and lower frame side TB mount and stock axle mount on one build. I don't know if the pitman arm was a reaction to the lower TB mount or the other way around.



I understand that good shocks can help on off camber sections, but it seems like shocks can only slow body roll and not limit it.

JeepWest posted a video of a SA TJ doing what normally will cause the drivers front to lift even roll in a parking lot. A few times it lifts the rear tire, which means there is a lot of rear roll resistance cause by high rear roll center? Is this evidence of geometry that eliminates jacking?





The places I wheel are somewhere in between. Our hills can seep water for days after a good rain keeping some obstacles slippery.

Front track bar and drag link have a symbiotic relationship that must be maintained unless you like bumpsteer. Tie rod and and drag links only like to operate in a certain range of movement. So depending on how much shock travel and what steering linkage is being used he may need to use a drop pitman and then drop the panhard to match.

Notice I said shocks and sway bars. Shocks dampen the movement sway bars resist it.

That sure did not look like a short arm TJ in that vid. It definetely had a mechanical locker or spool and a lot of anti squat though.
 
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i went through all of what your struggling with right now. asked all of the same questions and got just as frustrated.

when you start to talk about this stuff the technical end gets over peoples heads real quick, until you have some understanding of how the sys works.
this is why you get breadcrumbs until you start to learn and understand the sys and how it's parts control the suspension. until you understand this, nothing we say will translate into knowledge.

calc's are guesstimators at best since you don't have exact COG and weight distribution information.
i've seen and used several calc's and find none of them to include all the information needed.
things like drive bias or tire rolling radius or braking bias are not considered in some calc's.

don't try and start in the advanced class go back and start with basic suspension guidelines.
start with your chosen wheels size and work the problem back from there following just the very basic guidelines.

tire size (which is really the rolling radius) should be the 1st thing on your list and the location of the lower links on the axle would be next. just follow the trail and the design will begin to appear for you if you follow the guidelines.


now i saw 32" as estimated COG? from the engine crank? or top bolt of the bell housing?
mine with about 4" of lift was almost 36" to the bell housing bolt. i think the cranks to far forward for us, but that's a guess.
 
I am actually coming at it from a different direction altogether. I am working the 4-link calculator and trying to get the anti-squat to be as close to 100% as possible. I know that this is a single metric and perhaps not the holy grail but I am focused on it the most because it appears to be the metric that I can change the easiest. That being said, my axle mounting points are fixed. I have committed myself to 37" tires and I have 4.5" springs. The CG Height is what it is (assuming around 34" for my TJ) and that leaves placement of the frame side mounts as the only variables. So the longer the arms, the closer I get to 100%. Shorter arms yield me a higher percentage. So in a nutshell, that's why I'm advocating for longer arms. But I'm definitely not a suspension expert and am trying to get an answer as to why I might prefer a shorter arm. For example, I could see that have shorter lowers keeps the links out of the rocks and shorter uppers might triangulate the axle a little better and prevent it from wandering at higher speeds?

It seems that you have decided that you are keeping the lower axle side mounts, and placing your axle uppers on top of the truss. I'm guessing that will yield around 10" of separation at the axle. If I recall, that means you are going to want 7 or so inches of separation at the frame. You have two options. First, get those upper frame side mounts as high as possible... like lightly rubbing the underside of the tub kinda high. A body lift is pretty much required. The other option is lowering the lower frame side control arm mounts which sacrifice ground clearance. Somewhere in the middle is the right answer.

The problem is raising the upper mounts is that they will contact the tub at the rear passenger footwells. You can notch the floor, you can bend the links, you can make the uppers shorter to get around that tub. If the uppers are too much shorter than the lowers, the pinion angle at droop will cause binding. That's one reason to not go TOO long.

The problem with longer lower links is that at full compression the lower links will contact the frame... especially while twisted. The longer the link, the more of a problem this is. You can create a cross member to hang the lower frame side control arm mounts off of, but you are going to have to move the lower axle mounts closer inwards also. You can shave an inch or two off the frame to clearance the links, you add bump stop extensions, you can put a bend in the lower links. This is another reason not to go TOO long.

The final determining factor on arm length that I'm going to mention is the angle of the two lower links in relationship to each other. They are not parallel. The angle is actually very important in regards to roll steer. Lay under your jeep looking up at the links, draw an imaginary line extending the control arms towards the skid plate. That line is going to be where you want the links to mount. Notice that the only point at which the cross the frame rails is exactly where the factory put them. The longer the line the further it gets away from the frame. You are going to have to compensate by hanging the lower links off to the inside of the frame. the longer the link the longer the offset. Deviate from this imaginary line to much and roll steer will make the jeep scary to drive at high speed. I think you will wind up with a link around 26-27 inches. When you start actually cutting and welding and adhearing to certain parameters, you find that there really is only one place to mount the links and they have to be a certain length. Anything else and you start to compromise too much.
 
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And there ya go. That's why the tech is so low on this board.

Because my results with a spring change were different than toximus?

No other changes. It feels much better over pavement changes or manhole covers. The old front springs worked ok on bigger hits, but the old rear springs were harsh. I did not want to spend that money, but I feel it was worth it.
 
Because my results with a spring change were different than toximus?

No other changes. It feels much better over pavement changes or manhole covers. The old front springs worked ok on bigger hits, but the old rear springs were harsh. I did not want to spend that money, but I feel it was worth it.
What springs? Did the ride height change at all?
 
I assume they were Rough Country. The rear was sagging so I added a 1" spacer. New ones are 4" Currie CE-9132FP Front Springs and CE-9131RH2P Rear Springs. I did not measure ride height before and after, but there is no visible difference in height.
 
Unless you're running really heavy rated dump truck springs, springs don't effect ride quality.

Because my results with a spring change were different than toximus?

No other changes. It feels much better over pavement changes or manhole covers. The old front springs worked ok on bigger hits, but the old rear springs were harsh. I did not want to spend that money, but I feel it was worth it.

Or running a bad front to rear rate split causing a frequency imbalance. Some early lift springs had this problem. You would go over a speed bump and the rear would feel like it was slamming.
 
Or running a bad front to rear rate split causing a frequency imbalance. Some early lift springs had this problem. You would go over a speed bump and the rear would feel like it was slamming.

Good post. I recommend anyone interested in this kinda thing research Suspension Frequency. The front and rear springs work together. Remember the rear suspension has to do twice the work as the front and the relationship of the different spring rates matters in regards to motion ratios. The engineers at savvy knew this when selecting spring rates. I'm sure other high-end manufacturers do too. A blanket statement like "spring rate don't affect ride quality" is both correct and incorrect. It matters a lot, but not in the ways most people think.
 
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We have had the "frequency" discussion before and I was way out numbered. I believe it was a frequency problem and one reason I went with Currie was they mention tuning in the product information. @greaseorbounce might know something about spring frequency.
 
How can we choose a spring based on it's frequency? What does that look like?

When a coilover is setup, how is spring frequency incorporated into the selection of what springs to use?
 
Not spring frequency, suspension frequency. not the same thing.

Fine. What are examples of poor suspension frequency and good suspension frequency? What does that look like?
 
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An example of poor frequency would be rear springs that have a lower rate than the front spring. I ran an experiment on my own jeep after reading about suspension frequency. I removed my 2.5" rear springs with a rate somewhere near 180 and replaced them with factory TJ springs (I believe around 140) and a 2.5" spacer. So, shock bias was preserved. The jeep rode smooth enough but felt like shit. It bounced and lurched everywhere. I at first blamed the shocks thinking there wasn't enough rebound control (RS5000x). So then I changed the front springs to stock TJ springs with a 2.5" spacer... again, front and rear shock travel bias maintained. The jeep drove great. no bounce. no lurch. Then went back to my normal setup. 2.5" springs front a rear. Again, no bounce, no lurch. That's a bad suspension frequency. A good one is the opposite of everything I just said.

Do you own homework, I cannot properly explain something to you I can barely grasp. I did a test to confirm that there is something to the theory. That's why Brians jeep rode better after the savvy springs. Spring rate has nothing to do with ride quality. and everything to do with it. You're a big Savvy guy, you think they got the spring rates right on accident?