Not your mama's long arm debate

[Paul Ruggles]

Some of my friends and I built a single triangulated 4 link rear end for a CJ7 a few years ago, and we put 3 sets of holes 1 inch apart at the upper and lower frame end mounting points. Sort of like what drag race cars use for adjustment.

With the links in the center holes, it worked pretty good. Rear squatted just a touch when you stood on the gas, drove pretty good down the road, took bumps well. Then we started moving links to see what it would do.....

Wow. You could make it completely undrivable. At one point the rear would lift about 4 inches and the tires would just spin. It was a real learning experience ( that was why we did it. It was about 10 years ago when my group started converting over to coils from leafs).

Front ends started out as radius arms, they worked ok for what we did (fast bumpy trails, no rocks), short 4 links , a little bit longer 4 links, way too long 4 links, then kinda back to about 2 ft long links. No 3 links yet, I may try that on mine next.

The point is, if there is a point, if you do not want to cut and weld, and you are around 4 inch lift on a tj, just run short arms and good shocks. Be happy.

If you are ok with cutting and welding but are not willing to experiment, buy a Savvy mid arm. Its seems to be proven to do alot of stuff well. It climbs, goes fast, handles well.

If you are willing to do the old farmer cut and try (that's what my friends and I do because we are cheap bastards), build your own. BUT.....be prepared to do it over a few times. You will learn, but it takes time to figure it out.

 

[someguysjeep]

Hopping and jumping from the rear as the loaded suspension lifts the back end, loses traction, falls to the ground, regains traction and continues to cycle like that.

5:30 shows this behavior start to happen.

is it loading or is it the inability for it to load? low AS causes overloaded transfer to the rear and lifts the front? and high AS would not allow or retard loading, meaning it starts or tries to bite down but is forced out of the action by the high AS?

am i saying this right? i hope.

 

[mrblaine]

Wheel hop if you are pushing against a ledge.

I have never seen AS and IC numbers on long arms. How bad are they?

I don't do numbers. But, you and Josh have it correct. Pushes the back up until the axle can't climb under the rig any more, loses traction, pops back and repeats until it rolls, breaks, or makes it.

 

[mrblaine]

is it loading or is it the inability for it to load? low AS causes overloaded transfer to the rear and lifts the front? and high AS would not allow or retard loading, meaning it starts or tries to bite down but is forced out of the action by the high AS?

am i saying this right? i hope.

No, it is loading, loading enough to push the rear chassis up too much which lets the axle crawl under the rig until it breaks traction and then it slips back and repeats. What you would like to see is just enough AS to maintain full traction and not push the front down very much if any at all which is exactly what the mid arm does.

 

[Lilnuts]

No, it is loading, loading enough to push the rear chassis up too much which lets the axle crawl under the rig until it breaks traction and then it slips back and repeats. What you would like to see is just enough AS to maintain full traction and not push the front down very much if any at all which is exactly what the mid arm does.

With that said, is a good mid arm system the happy medium ?

 

[Brianj5600]

It has been stated in every thread like this that LA suspensions typically don't climb well. Is the lack of AS or the IC the cause or something else?

 

[jjvw]

It has been stated in every thread like this that LA suspensions typically don't climb well. Is the lack of AS or the IC the cause or something else?

The position of the IC creates too little AS.

 

[someguysjeep]

i have this BM'd for info purposes. if yall have a minute and can verify the information is accurate. particularly the footnote guestimations for particular applications.

https://www.crawlpedia.com/4_link_suspension.htm

 

[pcoplin]

When I accelerate from a dead stop the front end rises substantially. When I combine this with the basic geometry of the rear (10" separation at the axle, 3" separation at the frame, 12 degree rise on the lower arm, upper arm parallel to the ground), it suggests to me that I have a high anti-squat value. When I translate that to slick rock, it seems that my front end becomes light as the rear suspension compresses and/or the control arms experience pushing and pulling forces.

My assessment is that I would benefit from a more neutral anti-squat status. It's clear that more separation at the frame is needed. Burkey says to keep the upper arm flat or, I guess, parallel to the ground and keep the lower arm below 10 degrees. When I asked about lowering the frame mount earlier in the thread, @mrblaine replied that wasn't a good idea:



I'm still pondering this. Raising the upper mount will certainly raise the instant center. It also seems like it will raise my anti-squat value as well when I think it is already too high.

Care to identify the flaws in my hypothesis?

On the other question. Stock jeeps seem to go up slopes with no problem when I have to be extremely careful. Some of these are lifted (though not extreme) and seem to be on regular or short arms.

Is your front a radius arm style long arm?

 

[pcoplin]

The position of the IC creates too little AS.

Too little for what?

We run quite low AS, I prefer it that way. I build midarms with less AS than others, but there's no detriment on any of them, just a different focus on how we prefer the rig to handle.


edit: It's been a while (like years and years) since I've plugged in a lift like RE into a calculator, but you'll be surprised how high of AS it runs. It's due to the lack of frame side separation, and short IC.

 

[jjvw]

Too little for what?

We run quite low AS, I prefer it that way. I build midarms with less AS than others, but there's no detriment on any of them, just a different focus on how we prefer the rig to handle.


edit: It's been a while (like years and years) since I've plugged in a lift like RE into a calculator, but you'll be surprised how high of AS it runs. It's due to the lack of frame side separation, and short IC.

How does your mid arm behave differently than Savvy or a RE long arm?

 

[pcoplin]

How does your mid arm behave differently than Savvy or a RE long arm?

Did you just answer a question with a question?

The RE long arm hops on climbs, front radius arm lifts.

This is what I have noticed: The Savvy kit is very neutral on AS, climbs good, accelerates flat. Dave's has a higher AS, great road handling, hardly any roll steer. Mine squats more (this not not equate to front end lift), and works well with the higher wheel speed "bumps" we have to do around here, and also at Moab. I will say that I don't have any sort of production suspension. I make as I go, and can build higher AS if that is desired.

 

[Chris]

Did you just answer a question with a question?

His part time job is writing the questions for Jeopardy

 

[kmas0n]

His part time job is writing the questions for Jeopardy

He's being mysterious, like Andy from the 40 year old virgin. Chicks love it

 

[Chris]

He's being mysterious, like Andy from the 40 year old virgin. Chicks love it

Fast forward to 1:30. I'd almost forgotten about this scene, thanks for the laugh out loud! This thread needed some humor

 

[pcoplin]

The iteration of my Jeep currently has a little too much AS for what I like to do down in the desert. But for around here it does great. As you can see by this video it's very neutral when I'm on the gas.

edit: and yes it's a dreaded "long arm".

 

[someguysjeep]

This is what I have noticed: The Savvy kit is very neutral on AS, climbs good, accelerates flat. Dave's has a higher AS, great road handling, hardly any roll steer. Mine squats more (this not not equate to front end lift), and works well with the higher wheel speed "bumps" we have to do around here, and also at Moab. I will say that I don't have any sort of production suspension. I make as I go, and can build higher AS if that is desired.

this is kinda what that link eluded to, higher speed and bumps would handle better with lower AS.

• Anti-squat between 10% and 50% works well for high speed desert racing.
• Anti-squat between 20% and 80% works well for open road racing and rally racing.
• Anti-squat between 70% and 100% works well for rock crawling and trail running.

now don't bash me if these #'s aren't right , i asked if yall agreed with them, or not.

 

[Goatman]

First off... I neither want nor need a long arm suspension in my Jeep. Every single one I have seen going down a highway is either in the slow lane doing under 60 or in the middle lane trying to keep at least one tire in their lane. On a good windy day they look like sailboats leaning into a turn.

Second off... I find it humorous that so many people get twisted up when told they are wrong.

Third off... I find it humorous when someone posts Don't believe what you read on the internet. Hmmmm. Even funnier when the then give a link to prove they are right.

Fourth off... this started as a design question, but as always the 'anti' long arm folks always change it to a kit designed arm. Even when it starts specifically stating not talking about anybody's kit system.

Fifth off... I'm curious why drop brackets are always dismissed as a way to improve control arm angles to allow easier uptravel over obstacles. Every Monster Truck uses huge drop brackets. But I guess they aren't designed to drive over anything.

Sixth off... being told that a great suspension is needed to drive at 5 mph makes me scratch my head as I climb on my tractor, whose suspension consists of a spring under the seat, as i drive 5 mph over rock walls and deep furrows with ease.

Sixth off (i think?)... this is the only forum i know of that let's people argue and cuss if necessary. Every other place will suspend you for saying . Free speech is rare nowadays. Love you guys. I've never minded being wrong as long as I learn why. And this is the only place that allows this anymore.

 

[Wildman]

First off... I neither want nor need a long arm suspension in my Jeep. Every single one I have seen going down a highway is either in the slow lane doing under 60 or in the middle lane trying to keep at least one tire in their lane. On a good windy day they look like sailboats leaning into a turn.

Then you haven't seen very many longarm TJ's going down the road. Mine does 70+ MPH no problem. A stock TJ gets blown all over the road if the wind is strong enough. And if you don't want or need then why are you reading about it??

Second off... I find it humorous that so many people get twisted up when told they are wrong.

Your wrong...…

Third off... I find it humorous when someone posts Don't believe what you read on the internet. Hmmmm. Even funnier when the then give a link to prove they are right.

If this was really true then why do we believe ANYTHING we read on the internet?

Fourth off... this started as a design question, but as always the 'anti' long arm folks always change it to a kit designed arm. Even when it starts specifically stating not talking about anybody's kit system.

Becasue other than those who are building their OWN longarm suspensions the only other way to get one is in a BOLT ON KIT...

Fifth off... I'm curious why drop brackets are always dismissed as a way to improve control arm angles to allow easier uptravel over obstacles. Every Monster Truck uses huge drop brackets. But I guess they aren't designed to drive over anything.

I'd hedge a bet becasue monster trucks aren't trying to rock crawl thru some of the places folks take a Jeep. If the lower control arms from a longarm kit gets hung up on obsticals they why wouldn't drop brackets?

Sixth off... being told that a great suspension is needed to drive at 5 mph makes me scratch my head as I climb on my tractor, whose suspension consists of a spring under the seat, as i drive 5 mph over rock walls and deep furrows with ease.

Want to see you take your tractor to some of the places people take a Jeep.....

Sixth off (i think?)... this is the only forum i know of that let's people argue and cuss if necessary. Every other place will suspend you for saying . Free speech is rare nowadays. Love you guys. I've never minded being wrong as long as I learn why. And this is the only place that allows this anymore.

Then you sure the hell ain't been on Pirate....

 

[Brianj5600]

Sixth off... being told that a great suspension is needed to drive at 5 mph makes me scratch my head as I climb on my tractor, whose suspension consists of a spring under the seat, as i drive 5 mph over rock walls and deep furrows with ease.

If you are going 5 mph there is probably a good reason. Pretty much every time I have been in a sticky situation it was below 5 mph and never on flat ground. Off camber, descending and climbing is when you notice the shortcomings. Things like low speed damping, spring rates, roll stiffness and geometry all come into play.

I've never minded being wrong as long as I learn why.

Ditto