Rear links. How long is too long?

[kake]

Vehicle-1972 FJ40, radius arm front/coilovers, 4 link rear tj coils.

My original plan was to run about a 96" wheel base and keep my 37 inch tires from hanging out the back. Now, I a purchasing some unlimited LJ crusher corners and making some what of a CJ 8 type rear (kind of a mini-bed). So this means I can extend my wheel base even further. I was thinking 98-100". My lower links currently 36" long at about 12 degrees downslope. So to achieve 98-100" my links would need to be about 38-40". I really don't want to move my crossmember back (the links attach to this which would allow for a longer wheel base) anymore as it would hit the transfer case with out modification.

Question:

How long is too long for lower links? Is there any real formula? Is losing ground clearance my only issue? Any opinions welcome.

 

[I Lean]

Speaking strictly on suspension performance, longer is better. Real-world, longer links are easier to bend, and get hung up on.

That said, even 40" isn't ridiculous--although it is on the pretty damn long side of things. Just for comparison, the Teraflex TJ longarm kits use ~32" links, which makes the Unlimited kits ~42". Those rear lowers are bent for better clearance in the long version.

 

[jswainthug]

As long as the geometry works there is no length restrictions.

 

[Vonski]

As long as the geometry works there is no length restrictions.

I'll agree with this, but I can see two main issues with links in excess of 48".

(1) Unnecessary waste of material.
(2) Links that are potentially more likely to contact rocks/ledges. Also, when this occurs, they are more likely to bend.

For example, this morning I built some links that are 55" long. The customer is linking the front of his Blazer and would like to have his mounts in a particular location on the frame (which is his choice, as he is doing the install). The links are built from 1.75 OD .281 wall DOM, then they will be sleeved over with .120 wall DOM material (which is a good idea, especially in this case).

Of course, the longer the link, the more likely it may bend when coming in contact with rocks/ledges. As we all know, you can bend any link if you try hard enough, regardless of the wall thickness.

 

[rockdog]

Mine are 36" and they're all self clearance d ..... err I mean bent.

 

[Chevycrew]

I went with 48" lowers and 36" uppers. But I spent hours looking at mounting points and using the 4link calculator.

Thats just where mine worked the best.

 

[jswainthug]

As long as the geometry works there is no length restrictions.

Mine are 50 inches and I rarely hit them, but I took along time picking mounting points as well as the geometry.

 

[STAG]

The 4-link calculator that I use allows you to enter the type, size and thickness of your tubing links, and you enter in the weight of your rig, and then the length of your links, and it will tell you if you will bend your lower links or not when you get the weight of your rig resting on your link. Not sure how accurate it is, but its a good idea to check out.. obviously the longer the link the easier it will bend, and you may need to sleeve it with another DOM tube, as mentioned by Von.

 

[kake]

My thumb and eye seems to make a good calculator--JK. I haven't used a calculator so far, but I have done some math and tried to stay as close to a "proper" 4 link geometry as possible. My main concern with these links is ground clearance and strength. They are 1 3/4" x .281 wall DOM. How hard are these to bend in a bender?

 

[I Lean]

My thumb and eye seems to make a good calculator--JK. I haven't used a calculator so far, but I have done some math and tried to stay as close to a "proper" 4 link geometry as possible. My main concern with these links is ground clearance and strength. They are 1 3/4" x .281 wall DOM. How hard are these to bend in a bender?

In a tubing bender like a Pro-Tools, JD2, or equivalent--next to impossible. In an el-cheapo Harbor Freight pipe bender, not too tough to bend.

 

[kake]

Good, cause thats all I have access to right now. It's a hydraulic pipe bender (tube folder) with a 15 ton ram. Anything I should watch out for? Tips?

 

[Anchor_Mtn]

I have always used lower links that were a little more than 2x as long as the stroke of the shock I was gonna use. Its always seemed to work out well for me. I have 35" lowers with 16" Stroke coilovers. My lowers are 2" OD 7075 solid alum, No bends.

 

[waynehartwig]

My rear lowers are 36" and my front lowers are 40", if I remember correctly. With my lower belly, I seem to sit on them a lot. I don't think I've been hung up on them, though... Personally, I think mine are too long for the amount of lift I'm running and will probably shorten them up a bit at some point.

 

[UNSTUCK]

If the front of the links stick out past the front bumper, they might be too long. Almost sounds like a red neck joke...

 

[rholbrook]

A couple of weeks ago they went over this on Extreme 4x4.

http://www.powerblocktv.com/site3/index.php/watch-full-episodes/ep?ep_num=XT2009-07&ep_show=XT

Here is a link to the episode.

Good Luck

 

[STAG]

I watched that episode when it aired, it just says that your uppers should be 70% the length of your lowers, and that your vertical separation at the axle should be 25% the height of the tire, and the vertical separaration at the frame end should be half the vertical separation of the axle end... it doesn't say anything about choosing a link lenth to best work for your suited needs.

What I'm doin on my build-
http://img3.imageshack.us/img3/5840/dk2wu0.png

As you can see, my link lengths are about 32" for my uppers, and about 44" for my lowers. (32" is ~ 70% the length of 44") Now these are pretty long lowers when compared to most kits but I will be running a 40" tire, and I will double sleeve my lower control arms. Also I have a pretty long wheelbase. (108") and lastly my control arms are angled inwards a little more than most aftermarket "bolt on" kits.. which allows me to have a little more length in my lowers w/o going too far forward...

So what are some of the specs on your rig you're building kake?... tire size? wheel base? expected travel amounts? amount of lift?

 

[kake]

I was waiting for somebody to call me out for pics. I will get some up. I really wanted to get these LJ fenders (picking them up friday) on to give a glimpse of what I am planing.

I am using all of the ratios mentioned and then some. I am confident in my current design, its just the longer link thing bothering me which has come about due to streching my wheel base even more. These fenders were a recent idea.

 

[kake]

Took longer than I thought to get the crusher corners. Here is what they look like. 43651.
This will allow me to stretch my wheelbase to about 102". It also gives me more room for a fuel cell and spare tire. I have to have a back seat (3 kids) so this will allow me to do so. Basically this is a stretch on the cheap and I get the added benefit of tube flares and tough fenders.

As far as the links are concerned, I am just going to move my crossmember (my lowers connect to this) about 5-6" back and avoid having links over 42". Here are a couple pics of my current link set up. [/ATTACH]

 

[utah340six]

isn't the farther out you get the links on the axel the better off you are????????/

 

[STAG]

isn't the farther out you get the links on the axel the better off you are????????/

You are correct.. those lower links should be mounted out wider... the closer in you have your link mounts, the more leverage you are putting on the link ends when you push your tire up against an obstacle... and the more likely you are to have a failure of a link end, or link mount....