2.5 inch kj lift

[TwoBobsKJ]

Everything Tom said! :smokin:

For clarification...The front SHOCKS are the same length whether your Jeep is lifted or not. The lift doesn't come from the shock length but the lack of compression of the spring, the thickness of a top plate (if one is installed) and/or the amount of lift on the clevis. Longer shocks in the back are necessary if you lift.

Bob

 

[sexygirlfriend]

Hmmm. Lets see, how to get into this...

Let's start with the back, because that's a piece of cake. Yes, we lengthen the shocks when we install taller springs so that:

We don’t extend the old, shorter shock to its max when the suspension is in full droop.

We install a taller bump stop so that:
We don’t fully compress the new longer shock (that is in the shorter shocks same position) when we are in full bump, i.e., compression. It's more desirable to limit in this way than lowering the bottom mount any more than it already is.

By doing this we have increased the range / travel of the system while increasing the ride height of our vehicle. Which is good, that's what we want.


Now the front of the vehicle.

Ideally, we would like to do the same exact thing. Increase the travel of the system while raising the ride height. Agree?


TwoBobs you eloquently defined the problem in one sentence, "The front SHOCKS are the same length whether your Jeep is lifted or not."

There are simply no struts available other than those that are the stock travel length. Let's talk travel only at this point. The Rancho's and other stock replacements like NAPA, seem to have a travel of 4.25 inches. The OME's are at 5.2". For the life of me I cant find a Bilstein spec sheet anywhere, so I don't know where they are at. Somewhere in that range no doubt.

I think this is going to be long and painful, please bear with it. The scattered thoughts will eventually come together.

Let's design a suspension. For the time being let's not worry about the upper A arm / spring contact and look the other limiting factor, the max lift we can put on the CV joint axle and not have it bind up.

This is why I was asking the question about the max droop you guys had after your lift. I guess I'd just try to measure it, but I'm on the road in a hotel for the next few days. Let's make an educated guess of 5 inches.

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I did some measuring and it seems fairly accurate that the distance from the lower control arm frame axis to the ball joint is 16", and the strut is located 6" from the ball joint. This sets up a ratio at 16/10, or a 1.6 factor for force and distance calculations at the wheel vs. the strut. (I've seen a factor of 2 all over the forum).

So with that factor, when the axle displaces 5", so does the ball joint, and the strut displaces 3.125"

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That's a total of 6.25" travel at the strut. But remember... the LONGEST travel strut available was 5.2". This makes sense really; we assumed the 5" up and down. No manufacturer on earth would design their suspension to go right to the limit of the CV joint.

But we want to

We just cant do it, because 5.2 is the biggest. That equates to 8.32 inches of travel at the wheel:

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So where are we? We want to get THE MOST lift possible out of this situation that we can right? So lets design the bottom (extended) range of the strut to correspond to the max deflection of the CV joints. In this case 5".
RIGHT NOW it is not our concern as how to LOCATE the strut there. That can be achieved with shims / spacers at the top of the strut or "clevis" lift as you've termed it.
Or things like this:

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Since we only have 8.32 inches of travel at the wheel available instead of the full ten, we get something like this:

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That kinda *****, but it gets worse...

From what I can see, the axle shaft between the two CV joints is pretty much horizontal for a stock ride height. Let's assume it is.
We want to design a ride height 2.5 inches above stock. After all that's the name of this thread right?
Here you go:

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Now to the math. Let's define "Wfw" to be the weight on the front wheel and "Wfs" to be the ‘weight’ on the front strut. They are related by a factor of 1.6.
Wfw x 1.6 = Wfs

From what I can find (and why I was asking) is that a stock kj curb weight is 4115 pounds with a distribution of 53% front and 47% rear. That comes out to 1090#'s at one front tire. Let's say we have a big bumper and maybe a winch and some lights and other $hit hanging off the front. Maybe 180 or 200 pounds worth. AT THE FRONT axle, that weight is amplified a little bit because of the fulcrum. Let's say it's pressing on the struts/springs with 265 pounds or 132.5 pounds each side. That's not unreasonable, and the reason for such odd figures will be apparent.

Now lets use the recommended strut and spring combo:

OME's NS-131 strut with 5.2 inches travel, and an extended length of 333mm or 13.11 inches.
OME's #927 spring, with a 400#/inch spring rate (after all we have a big bumper and winch!) and an uncompressed length of 394mm, or 15.5 inches.

(15.5"-13.11") x 400#/inch = a strut preload of 956 pounds.

We said the jeep weighed 1090 plus 132.5 pounds at each tire, or 1222.5 pounds. Multiplying by 1.6 to get the "weight" at the strut yields:
1956 pounds force, provided by the spring/strut to support the vehicle. So factoring out the preload of 956 pounds, we will need to displace the spring SOME DISTANCE such that the force required to do so will be 1000 pounds. That's at the strut.


That's easy math, 1000 pounds, 400 pounds per inch, 2.5 inches! Cool right? That's our lift? Not quite, that 2.5 inches is displacement at the STRUT. That means 4 inches at the wheel. Turns out it's only a 1 inch lift kit.

But hey, we can fix that with shims and plates and "clevis"! (Yes there's a slight error in the math here... you guys are only adding .325" of top shim and .325 of clevis offset for .75 inches at the strut, not the .94". [.94 inches x 1.6 is 1.5" at wheel, plus the 1" is a 2.5" lift] So the math is off by .18" but remember... we assumed that the stock ride height equated to an exactly horizontal axle. At least I think that's what is causing the inconsistency!)

So that's what we do. We offset the strut to give us the lift we want, with the given weight and spring rate of out truck.


Now lets look at the real problem with this.

The strut is displaced 2.5 inches to provide the required force to lift the vehicle weight. There is only 5.2 inches to start with, so that leaves us with 2.7 inches left to displace before the strut hits the stop (and I don't even think it has an internal stop at that end.) That 2.7 inches at the strut equates to 4.32 inches at the wheel.

What you end up with is a limited range that looks like:

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And the bottom 2.5 inches is only available in droop. (like if you jacked up your jeep from the 'frame' and let it the wheel hang.)

Now it is a sound design with respect to things like... getting your lift where you want it, Not busting a CV, supporting your cool winch, etc. And don’t get me wrong, it will feel great to drive around, responsive with limited body roll. But it's akin to putting blocks under an indy car. It's really stiff and responsive, and it's really high.

By the way if our strut is shorter than the 5.2 inch OME, it reduces the usable travel EVEN FERTHER!



God that was long. I sure hope my math is good and I'm not just spraying a bunch of $hit. It begs the question though:

What should we do now?

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Well we need is a strut with full travel. Let's say we could find one. 6.25" minimum if we really do have 10 inches (5 up and 5 down) of usable axle displacement. We can still preload a 400 pound spring 2.4 inches to yield 956# and add 2.5 inches of displacement to arrive at 1956 pounds force at the strut, which will hold us at 2.5 inch lift, but the spring is going to have to be longer. And we are going to have to fab up the mounting for it.

I haven't done the math on this but I suspect that a strut with an even longer displacement could be used with a lower preload and weaker spring if it were mounted more compressed. Of course that would take away the lower bump stop that limits the system extension. Gotta figure that out I suppose.


So this is the impasse. Has anybody cracked this code? Gotten full travel out of their lifted IFS? I haven’t found a strut like I'm thinking this needs yet. Although a strut cartridge like this might have potential:

http://catalog.monroe.com/catalogPa...CTIVE&locale=en&methodName=displayPartDetails

It would require fabricating some sort of clevis and spring seat though. Not to mention poke out the top mounting a bit, a mounting that will have to be fabricated.




Thanks for reading tonight's novel. Next chapter: Roll Centers.



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[tommudd]

I think
ONE; you have way too much time on your hands
TWO; you need a real hobby
THREE; over thinking a problem can sometimes be worse than not thinking about one
FOUR;
in the real world sometimes things are a little different than they are on napkins
and you don't need a slide rule to figure that out :happy175:
Now granted if you were building a full on race say KJ for extreme 4 wheeling then yes you may want to go to those lengths to figure out how to get the most out of that vehicle. But for what we do, how we use them and where they will go what has been used works great. I know a lot of people who have been lifted over 100,000 miles me included and the setups we use although all are not exactly the same they are close.
But if you have that much time, that much energy then have fun and find your ultimate flex

 

[TwoBobsKJ]

Lauren (or Lauren's boyfriend :smokin: )

Couple of things. First, I wish I had the genetics that would enable me to speak math as well as you do! I trust your calculations cuz I don't know how to de-construct them!

Second, I believe the original stance of the Liberty caused the front axle between the CV's to be slanted down toward the wheel as the original ride height was high enough to cause a natural "droop" of the axle.

Third, because all of our Liberty's came with crappy springs from the factory we all had sagged suspensions - some lower than others. The problem I've seen throughout these forums is a misunderstanding of the amount of lift generated by an OME/Bilstein or other lift kit. The baseline is different for different manufacturers and those who communicate the specifics of their kits only add to the confusion since they're all working from a different starting point.

The baseline sag from factory stock height is broadly defined as being about 1"; when you go to JBA's site and read his OME descriptions note that the lift attained is said to be 1.5" and many assume that the kit must be just a small, incremental lift. The reason OME states 1.5" vs 2.5" is that they are working off the stock ride height - not the lift gained from the sagged ride height. In other words, if my Libby sagged 1.5" from factory height (down to 17.5 from 19) my OME lifted height would be 3" or more higher than my tired ride height with bagged springs. Wow - I must have gotten a special lift from OME cuz I'm ridin' higher than JBA said I would! Wrong...It's just that my Libby was a lo-rider before I put the lift on.

As far as cutting the CV's to get the necessary travel...There is an excellent post from tjkj2002 showing the guts of the CV's and what happens to them when 3/8" is removed to eliminate binding. It ain't pretty and his explanations cured me of ever wanting to go that route.

Unless and until you choose to go SFA on your Jeep the articulation on the front end will be limited to about a 5" swing. But given that many here have lifted their Libby's up to about a 23" or so height - and have amazingly capable off-roaders - there is a lot to look forward to with a lifted Libby.

As for the weight of an ARB with a winch and what that will do to the front springs - back to math class for me... :freak3:

Bob

 

[sexygirlfriend]

He he. Yea maybe you're right. I've been on the plane about 16 hours in the last 4 days and have had lots of time to think, draw pictures on napkins, etc.

But that's easy stuff and more importantly it's free (and so are you guys!).

A few years ago I researched picking up my 4wd Dakota. It's IFS with torsion bars. I did engineering in college and needed to get smart on suspension. A book called "fundamentals of vehicle dynamics" by Gillespie is the bible on the subject. Read it cover to cover.

Turns out, instead of building a sweet pair of 4-links, I built a monster small block and just added a leaf and tightened up the torsions.

So since we've brought Laurens jeep out to MT from the east coast last month, I've been stoked to build the suspension that I never got to. I'd love to do a solid axle swap (hmmm sounds like another sweet 4-link set up again). But frankly the vehicle isn't worth putting more than 2 or 3 grand into. It's got a fair amount of east coast rust under it.

But I'd still like to design and build for performance.

I think I'll do another day of looking for parts and drawing on napkins, then come up with a plan and start tearing shit apart. I appreciate the your guys time. I'm sure I'll bounce more ideas off you if that's cool. I'll probably start a new thread if I come up with something innovative; Show off the process in case somebody wants to do something similar.

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[sexygirlfriend]

Hey it looks like the stock Upper control arms have a fixed ball joint? They make you replace the entire control arm when the ball joint wears out?



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[Ry' N Jen]

Hey it looks like the stock Upper control arms have a fixed ball joint? They make you replace the entire control arm when the ball joint wears out?.

Yes, you are correct!
When the ball joint packs it in, it's time for a new/remanufactured upper control arm.

 

[holmadik]

bottom line do you actaully need to change shocks and struts right away when you put on OME springs?

 

[TwoBobsKJ]

bottom line do you actaully need to change shocks and struts right away when you put on OME springs?

Do you NEED to? No, but...

Much better to wait since the process of replacing the front shocks requires you to disassemble the front end - the same process you use to replace the springs. You'd be doing double the work besides taking a dump on your new springs with old shocks. Plus I saw on another post that you want to do a winch and bumper - wait till you get all the parts and then do a lift with the proper springs to support your bumper. Higher rated springs don't cost any more than the Mediums or HD's.

I was excited to lift mine too but I took other's advice and purchased the parts over the course of a few months and then did everything at one time. Unlike TomMudd's Jeep mine actually requires ME to disassemble it to change or add something. Tom whistles at his and the wheels come off and clevis bolts come out somehow... :hail:

Bob

 

[501]

Unlike TomMudd's Jeep mine actually requires ME to disassemble it to change or add something. Tom whistles at his and the wheels come off and clevis bolts come out somehow... :hail:

Bob

:laughing1:

 

[jeremy1r]

banging sound from rear

I have the typical ome lift set up minus a cleavis lift, have noticed loud baning noise from rear, sounds like rear shocks are too long? and bottoming out. went with heavy duty rear ome's and one extra isolator. runnin rear dakots shocks. any suggestions

 

[Cardhu]

I have the typical ome lift set up minus a cleavis lift, have noticed loud baning noise from rear, sounds like rear shocks are too long? and bottoming out. went with heavy duty rear ome's and one extra isolator. runnin rear dakots shocks. any suggestions

http://www.jeepkj.com/forum/f202/how-install-rear-bumpstops-hockey-puck-version-43989/

will also keep your eventually bigger rubber from tearing off your fenders. 2 will be fine for up to 245 75 16's or 31's.

its easier to drill the spring perch with the springs out.

 

[Luke]

its easier to drill the spring perch with the springs out.

.. and with a right angle drill

 

[jggv98]

I have the front and rear coils OME 927 and 948 ready to install in my 2004 kj, what option do I have for the struts and shocks after the rancho RSX 17505 are discontinued?

Thanks

 

[ThunderbirdJunkie]

Get Bilsteins. Ranchos are just Tennecos and ITBJHO, have NEVER been any good.

 

[jggv98]

What about the ranchos RS5000 front struts and rear shocks?

 

[jggv98]

Ok I found that the only way to go with ranchos is on the rear suspension with the RS9000XL with lift

Are they ok?

 

[TheBlueKJ]

... Don't do Ranchos like TBJ just said. They're quality has greatly declined so just go with Bilstiens.

 

[Outofideas]

What about the ranchos RS5000 front struts and rear shocks?

That's my setup with ome coils. I think they are soft. I should have spent the few extra $ for better although I am overall happy with them. The front seems fine but way too soft for my liking in the back especially with towing a trailer. The rear squats way too low loaded. Trail wise they seem ok but I have no previous experience to compare them to. I'm probably going to upgrade the rear shocks soon.


Sent from my iPhone using Tapatalk

 

[deanoo]

theres nothing wrong with spacer lift...the spacer lift im doing you dont compress the spring this one im doing is pretty much an extension the the strut but thats besides the point of my question...im doing the 2.5in spacer kit will 255 75 17 fit?