Suspension travel upgrades on an 80

[SUMOTOY]

Man, there is a lot of info in this thread...

Yes there is. And I'm intrigued by some of Nay's suggestions early on. A bit of baseline regarding WE thoughts on frame drop vs axle mounting lift contains errors we should correct. Specifically referencing WE comments in posts 15 and 18.

Wrong. The path the tire moves with a radius arm is going to be determined by the arc from the center of the tire to the mounting point of the arms. This isn't changed with caster plates, caster bushings, or raising your axle mounts. When you move the frame mounts, then you move the motion of the axle/tire relative to the frame. So it's not "the exact same effect".

Depending on how you raise the axle mounts, you can also create a bunch more leverage on the suspension. In the front, if you flip the arms, the center of the axle is still the same distance from the arm (more or less), it's just on top rather than on bottom. But in the back, if you start raising the mounts on the axle, it's going to get more leverage for bending the links.

Let’s get some baseline here. I was just starting to note Nay’s ideas carefully, as modifying a stock height truck has its merits.
We, the path the tire moves with the radius arm on the 80 depends exactly on which axle you are speaking to. In the case of the front, you are correct, the instant center (the pivot point for drawing the tire radius arc) is the mounting point of the arms at the frame.

However, in the 4 link rear of the 80, that statement is no longer true. The Instant Center for the tire/axle radius arc is located where the lines extending forward from the upper links and the lower axles intersect (the virtual pivot point to draw the tire radius arc). That is much further forward than the actual mounting points on the frame.

The radius arc is indeed changed by caster plates and or bushings, in either the front or the rear. If you change the effective length of the rod/s, you change the path of the arc, specifically you redefine the radius of the arc.

Regarding Nay raising the mounting points on the axle vs lowering the mounting points on the frame, they indeed are “the exact same effect” in terms of what it does in geometric terms. In the front if you lower the top pivot (at frame) 2inches or raise the bottom pivot (at axle) 2 inches, you have reduced the angle of the link rod (to axle) by the same amount in either scenario. If the rod length is the same, and the changed angle is the same, the tire arc is the same.

Raising the truck causes leverage on the suspension, not the mounting of the arms (frame dropped or axle raised). The stress is identical because the angles are identical.

It might be worthy to note or discuss in the rear, you can actually change (reduce) caster changes by moving the lower mounts up, and leaving the tops alone. Why? Because the Instant Center (upper link stays the same, raising lower link reduces it’s angle, so the intersection moves forward) is now even further forward of the actual frame mount, causing less caster changes (read larger radius arc) vs raising both mountings together. This doesn’t speak to resultant mechanical problems (i.e. pinion angle), but it does speak to arc and travel.

Rigid axle suspension geometry is pretty well documented. It should be noted that Nay has made correct statements regarding drop frame or lift axle mounting as “the exact same effect” as he described.

Scott Justusson
QSHIPQ Perfomance Tuning
94 FZJ80

 

[Tools R Us]

....

Rigid axle suspension geometry is pretty well documented. It should be noted that Nay has made correct statements regarding drop frame or lift axle mounting as “the exact same effect” as he described.

Scott Justusson
QSHIPQ Perfomance Tuning
94 FZJ80

True, the geometry is the same, but by lowering the rear mount you create a new rock hang point and the whole arms are down in the rocks. By flipping the arms you cure the rock magnet of the arms hanging down under the axle.

 

[Walking Eagle]

Rigid axle suspension geometry is pretty well documented. It should be noted that Nay has made correct statements regarding drop frame or lift axle mounting as “the exact same effect” as he described.

It should be noted that Sumotoy often confuses rigid axle with IFS.

 

[landtank]

By flipping the arms you cure the rock magnet of the arms hanging down under the axle.

Has anyone actually done this in the US?

 

[alkaline747trio]

Nobody knows fully the answer to my question, or is it being ignored. With everything stock, what is the faulty point in the suspension reguarding droop/compression?

 

[Walking Eagle]

Nobody knows fully the answer to my question, or is it being ignored. With everything stock, what is the faulty point in the suspension reguarding droop/compression?

absolute stock, it will compress till it hits the bumpstops (and then like Slee says, compresses them some ammount). It will droop until shocks fully extend.

Articulation is a different question

 

[alkaline747trio]

So is there any droop or compression wasted in the shocks? And is this droop measured w/ or w/o sways?

 

[IBCRUSN]

Along with alkaline's question.

Is it possible/acceptable to run the L shocks with either stock springs or one of the OME low lifts to gain some articulation/travel?

 

[Cruiserhead05]

Its been discussed.

https://forum.ih8mud.com/showthread.php?t=60679

 

[landtank]

Along with alkaline's question.

Is it possible/acceptable to run the L shocks with either stock springs or one of the OME low lifts to gain some articulation/travel?

As far as the fronts go the OME Js would be the same as Slee's fronts as they are the same length uncompressed, I'm not sure about the rears.

 

[SUMOTOY]

True, the geometry is the same, but by lowering the rear mount you create a new rock hang point and the whole arms are down in the rocks. By flipping the arms you cure the rock magnet of the arms hanging down under the axle.

I agree, so does Nay (see post #2 - last sentence paragraph #2). I believe exactly what he is saying is that you Raise the axle mount, just as you describe, it's effectively the same thing as lowering the frame pivot point. I don't see anywhere that Nay or I indicated that one should lower the rear frame pivot mount. In fact, quite the opposite.

The point is that Nays presentation that raising the axle mounting point is indeed the same as lowering the frame mounting pivot, it is the same thing. WE ascribed that as wrong. It's a true geometry statement, *and* it accomplishes higher clearance as TRU has confirmed. TRU, you need to reread the post. Given it results in the same geometry, you agree with Nay and myself, that raising the axle mounting point is a better idea, and has the advantage of less hangup. That contradicts WE posts.

I look at a "wrong" statement very early in this discussion, that has no basis or support. Please feel free to put instant center solid rear axle in google to understand the concept better.

Again, I enjoy technical discussions, and I believe Nay was onto something good. It got hung up in bad geometry 'correction'.

SJ

 

[SUMOTOY]

It should be noted that Sumotoy often confuses rigid axle with IFS.

WE, an all caps 'wrong' is not confusing to me, when it's indeed right. Nay had it correct as stated (post #2 last sentence paragraph 2). You only had the pivot point half correct in post 15 (as it applies to the front axle), and the geometry in 15 and 18 is just not supported in theory or fact. It's ok, I still think Nay is on the verge of something good....

Thanks


SJ

 

[Tools R Us]

I agree, so does Nay (see post #2 - last sentence paragraph #2). I believe exactly what he is saying is that you Raise the axle mount, just as you describe, it's effectively the same thing as lowering the frame pivot point. I don't see anywhere that Nay or I indicated that one should lower the rear frame pivot mount. In fact, quite the opposite.

SJ

Sorry if it looked like I was disagreeing with you, I agree and was trying to add some clarification on the trail clearance of arms on top.:whoops: At least one vendor sells drop brackets for the rear of the front arms, no US vender that I am aware of sell an arms on top kit. The biggest hurdle I see for flipping the arms is fitting the sway bar.

 

[Nay]

Nay,

Do you have measurements of the compression and extention with your current lift? I am planning on going with the heavy lift so the specs should be close.

I don't yet - I need to get out a marker, flex it, and measure (I hate those damn metal boots...if it was just the bare rod with no boot I could just measure in my garage )

I'll be out on the trail this weekend and will try to measure and report back.

Nay

 

[Nay]

Along with alkaline's question.

Is it possible/acceptable to run the L shocks with either stock springs or one of the OME low lifts to gain some articulation/travel?

The basic OME shock is 10" travel, which doesn't sound like much in the world of 14" travel shocks, but is actually a ton of travel if you can use all of it (I only ran 10" travel shocks, properly positioned, on my former 8" lifted Jeep, and it was plenty of travel). The 80 front end is not coming close to using a full 10" of travel with swaybars connected. I don't think there would be anything to be gained by messing with the shock mounts or running longer shocks on a stock height suspension.

Now you extend those same shocks 2.5"+ with a lift kit and that's where the whole idea of having too much up travel and too much down travel comes from. You could go from 3" up and 7" down to 6" up and 4" down. The former is a pretty good ratio and you won't use that full 7" down due to front end bind, but the latter is not even close to optimal. You ideally want to add 3" of lift and have your shocks positioned for 4" up and 6" down - hence the ability to run larger tires and have the best travel possible within the stock design constraints. That simple issue is what is keeping OME owners on 33's just like their stock height counterparts.

Nay

 

[SUMOTOY]

Sorry if it looked like I was disagreeing with you, I agree and was trying to add some clarification on the trail clearance of arms on top.:whoops: At least one vendor sells drop brackets for the rear of the front arms, no US vender that I am aware of sell an arms on top kit. The biggest hurdle I see for flipping the arms is fitting the sway bar.

Thanks TRU... I figured you had it right, as did Nay. Regarding front brackets on the axle vs frame: I see a lot of potential issues there, the biggest being the arm reducing upward travel (hitting the frame) without remounting the arm inbound, which creates another set of issues.

Even a slight bit of upward mounting of arms on an axle results in more clearance, all else being equal. The side benefit is better bump geometry, and better ride quality. I'm not convniced we are speaking to a whole bunch of upward mounting on the front or rear axles, but on a stock height truck, it's free gain.

I will say too, that lowering rear frame mounts on the front arms may ultimately prove the better solution if going beyond raising the stock mounting point on the axle, because you generally go forward over obstacles, so the brackets aren't really an interference. That changes on the rear axle however.

SJ

 

[Walking Eagle]

Man, there is a lot of info in this thread. Just wanted to point out two things. Heath the above is true in the theoretical sense, however the rubber on the bumpstops compress and trail pressure on bumpstops are generally different to the ramp testing we do. We went with 2" to provide a safety gap.

Probably get a bit more angle on the axle too if you're compressing one side 4 or 6 inches more than normal, or a couple inches more than J's do. I'm sure that'll change how the tires stuff and where they hit. I know on my 40, articulating the tires stuff nicely, if I load it with 1,000lbs of edging stones and it compresses equally on both sides - it rubs the wheel well a little.

Definately more to be had on the 80 though. If you stay with the stock mounting, like you said, it's going to limit shock choices. It's going to be interesting as people start looking deeper into extracting more from the 80 with the stock or dropped suspension mounts (as opposed to custom links and mounts). Once people like actionjackson start messing with shock mounting and longer travel shocks, it'll be interesting to see what the next constraint will be.

It's kinda fun seeing where the next weak spot is. Sort of like having a Sweet Carver amp running high end speakers, and you're feeding it with a tape deck. It sounds great. But with a CD player it'd be that much better. I think that's sorta where we are with the stock shock mounts. We're stuck with a tape deck, which while it works, there is more potential in the rest of the components once we free ourselves from that constraint. Guess the downside is there is also alot more potential for cost

 

[Tools R Us]

Thanks TRU... I figured you had it right, as did Nay. Regarding front brackets on the axle vs frame: I see a lot of potential issues there, the biggest being the arm reducing upward travel (hitting the frame) without remounting the arm inbound, which creates another set of issues.

Agree, 6" or more of lift is needed to put the stock arms on top, the axle will needed to be bump stopped losing some up travel, but longer shocks are needed to get full travel and they need the extended stops anyway. that much lift is where the arm angle starts getting extreme, affecting ride and handling, I don't see any benefit to doing it with a lower lift.

...

I will say too, that lowering rear frame mounts on the front arms may ultimately prove the better solution if going beyond raising the stock mounting point on the axle, because you generally go forward over obstacles, so the brackets aren't really an interference. That changes on the rear axle however.

SJ

It depends on where and how you wheel, I have landed on the stock arms at the frame brackets a few times playing in the rocks, it hasn't been a problem, but I wouldn't want them any lower. The arms under the axle cause more trouble, they are easy to hang up on.

 

[Walking Eagle]

WE, an all caps 'wrong' is not confusing to me, when it's indeed right. Nay had it correct as stated (post #2 last sentence paragraph 2). You only had the pivot point half correct in post 15 (as it applies to the front axle), and the geometry in 15 and 18 is just not supported in theory or fact. It's ok, I still think Nay is on the verge of something good....

Thanks


SJ

let's see in post 18 I said

"No, the effect is not essentially the same. Raising the brackets on the axle will give put the suspension travel into a diffent part of the arc than dropping the brackets on the frame. You get more front to back motion."

here's a picture for ya'. The frame, though not drawn, is in the same possition for all 3 links. The green link would be equivalent to raising the brackets on the front axle with stock mounting location. The Blue link would be a stock link, stock mounting location. The path by the tire - in pink, is the the path either of these two will follow. Notice how much the tire moves front and back through the usable part of the arc. The black arm witht the black tire and arc would be like a dropped suspension mount. The arm is much more level and has less forward and backward movement through the same suspension travel. So the effect of raising the mounts on the axle is absolutley NOT the same as lowering the suspension brackets!

Before you state that my posts have errors that you need to correct or that what I said is not supported in theory or fact, I suggest you take the time to verify it. I'm not going to take the time to explain why it also increases the likelyhood of bending arms, you can look it up in a statics book and do the free body diagram yourself.

 

[SUMOTOY]

let's see in post 18 I said

"No, the effect is not essentially the same. Raising the brackets on the axle will give put the suspension travel into a diffent part of the arc than dropping the brackets on the frame. You get more front to back motion."

here's a picture for ya'. The frame, though not drawn, is in the same possition for all 3 links. The green link would be equivalent to raising the brackets on the front axle with stock mounting location. The Blue link would be a stock link, stock mounting location. The path by the tire - in pink, is the the path either of these two will follow. Notice how much the tire moves front and back through the usable part of the arc. The black arm witht the black tire and arc would be like a dropped suspension mount. The arm is much more level and has less forward and backward movement through the same suspension travel. So the effect of raising the mounts on the axle is absolutley NOT the same as lowering the suspension brackets!

Before you state that my posts have errors that you need to correct or that what I said is not supported in theory or fact, I suggest you take the time to verify it. I'm not going to take the time to explain why it also increases the likelyhood of bending arms, you can look it up in a statics book and do the free body diagram yourself.

WE:
The arms are different lengths in your drawing. If you have the same length arm, and cause it to be level, you have the same arc.

You need to make sure that Overall Length of Green = Overall Length of Black. Because you have done nothing to change the Overall length of the rod. Therefore the pivot point of Green and Black is the same at the "frame" and at the axle. Your drawing reflects Green having the same frame pivot point, but a shorter axle pivot point. How can that be if we are using the same rod and only changing how it is levelled?

You drop the frame pivot point straight down. OR you raise the axle pivot point straight up the same amount. That's all you can do in the exercise. 'Cutting' the green axle rod as your drawing reflects, is premature.

Scott