4 link for dummies

[Lars]

I just re-read some of the previous posts. Galen quoted from the calculator that in bending, a FS of 2 is probably plenty. I have to remind people (and especially myself) that I'm no expert here. I know plenty about structural design in general, but I've barely thought about the structural considerations of a linked suspension so I'm just this side of clueless. Having established that... since a suspension link has rod ends at both ends, the only way I can see that you can apply a bending load to a link is by coming down on an object. Or if you made a mistake in design and you exceed the misalignment ability of a rod end. Otherwise normally the only load is going to be in compression.

[Sillyneck]

omg you guys are too smart... I went w/ the philosophy major so I didn't have to work w/ numbers LOL Excellent info. Made my brain hurt.

my personal experience.....if your lower links are 2" .250 and the length of the actual DOM is 36" you'll be hard pressed to bend it. Denting? haven't seen much of that myself... maybe in a rockwell and 48+ tire smashin and bashin application they could get wasted. If it was going to be a 4'+ link (maybe a super extended bronco) I'd say get 500wall (380 is hard to come by around here) and drill the end to drop the insert in. I've never linked a bronco w/ anything longer than 40" lowers. they seem to meet right in the middle of the frame if both lowers are right around 40" hole to hole and that's w/ at least 5 more inches of wheelbase.

1.75" 250 is too weak for sure though. Didn't see anyone say anything about that... but it will bow in a bronco app.... it's onehelluva ride to bow it... but it will

[highlander]

Thanks, for your opinion Lars. As you said the bending FS is based on the vehicle dropping on the arm. So with the 2.25" x .375 wall it can (on paper) take ~4850# on one arm. I am pretty comfortable with that.

[crawlin68]

Valley Iron sells the 2.25 x .375 wall for $14.25 a foot. Not too bad. I think we can get three links out of a 10' piece. So a 20' stick would be $285. What do you think?

[highlander]

Valley Iron sells the 2.25 x .375 wall for $14.25 a foot. Not too bad. I think we can get three links out of a 10' piece. So a 20' stick would be $285. What do you think?

That will work for me. Do you want me to get it? It has to be special ordered right, can we order over the phone?

So what are your thoughts for your brackets?

[720Racer]

Valley Iron sells the 2.25 x .375 wall for $14.25 a foot. Not too bad. I think we can get three links out of a 10' piece. So a 20' stick would be $285. What do you think?

Double check that he has 20's, the salesman at Team Tube told be DOM is sold in 18' sticks (probably still enough, but might be a little short depending on how you design it).

[highlander]

Thanks, I would be fine w/ 9'.

[crawlin68]

Yeah it can be ordered over the phone. The guy said that it comes in randum lengths between 17' and 22', but you can specify a minimum length anywhere in between 17' and 22'. So if you specify that you need at least 20', it will be at least 20' long.

If you are going to be down in town, it would probably be easier for you to pick up in your truck. If not, I can get my trailer out and have them cut the stick in half for me. That way it will fit in my trailer. They are open on Saturdays until noon too. He said it takes a day or two to get it in.

[RJLougee]

Hey guys, thought I'd wade in here a little bit and pass some info along about what I've learned.

1. Earl M. Jorgensen is usually the least expensive place I've found to buy steel. I know they've got a bunch of yards and they deliver to most of the smaller places we buy steel from. They will sell to the little guy as well and you can get them to deliver to your town on a normal run. My closest one is in Denver, but they come down here 2x week and will bring a couple sticks down for me. They also have better pricing at the 2 stick level, so if a couple guys are doing projects you can get a better deal. My 2x.25" DOM is just over $10 a foot.

2. Red Rocks 4x4 is the best price (by far) I've found for JJ and a lot of fab parts. Off-road Overstock is another good source, as well as Rough Stuff Specialties. Also look in the Vendor section on Pirate.

3. http://www.aladdinsteel.com/ Aladdin Steel is a good place to look up steel to figure available sizes. If you're looking for 2+" DOM with and ID of 1.5" you can get several sizes. Also gives the weight per foot so you can figure out how much more unsprung weight you're adding.

4. Fastenall had the best prices on jam nuts and will usually have what you need in a couple of days.

Now on to some theory.

I believe a FS of 2 is plenty for the lower links. I'm running .25" wall 2" OD DOM and that's pretty good for a 3K# buggy.

Upper links will only see compression/extension forces on them so lighter is more than enough. 2" is overkill to a high degree. I'm using 1.375 x .188 wall tube.

It's nice to have left and right threaded joints at all the links so you can adjust them on the fly. Of course, then you should have jam nuts on all the studs.

If you want to use angled lower links you need to have a fixed bushing at one end, otherwise the link will rotate and give you a bunch of rear steer. Why angle the link you ask? For better ground clearance while getting the mounting point as low as possible on the axle tube (rear below).

Put a winch in back so you can pull the body down so the coilovers don't unload as the rear unweights on steep downhills. Do you need it? Maybe, maybe not, depends on how well the suspension actually works.

Unless $$ is really an object, and I know it can be, just go coilovers right off the bat. Or even air shox IF YOU ARE WILLING/ABLE TO WORK ON THEM TO GET IT RIGHT. You'll stand a much better chance of getting a coilover right than air shox and you'll need to reoil/recharge several times. If you do a cost comparison you'll find that $400 a corner for coilovers is reasonable vs. say a nice set of Deaver leaf springs ($450 or better by the time you get them home) and a set of good shocks ($375/pair for some Bilstein 7100s). Looks like $800ish to me and the ride won't be as good.

When you're running your measurements and making calculations, ensure you're making them the correct way. If the lower link is 40" long and at a 15 degree angle, it's placement on the X axis isn't 40", it's more like 38.5".

Build adjustment into the mounting points at each end of the upper links, that will allow you to change your anti-squat to dial it into what you want as you learn.

My definition of Anti-squat: the way the rear suspension will move as accelerative forces are placed upon it. So, a really low AS will cause the rear end to SINK upon acceleration and a high AS will make it rise. Front suspension will also play a part in this.

Gotta run,
Joe

[crawlin68]

Wow, that is all great info Joe! Thanks for your input. What kind of AS would you shoot for on big heavy rig like mine? What do think about using 1.5 OD x .25 wall tube for my upper links?

[720Racer]

My definition of Anti-squat: the way the rear suspension will move as accelerative forces are placed upon it. So, a really low AS will cause the rear end to SINK upon acceleration and a high AS will make it rise. Front suspension will also play a part in this.

Joe,

Thanks for sharing with us. As for Anti Squat, with low AS causing the rear end to sink, and high AS causing the rear end to rise, what % AS would be neutral?



Galen

[crawlin68]

So what are your thoughts for your brackets?

I'm not sure yet. I don't think that I am knowledgeable enough yet to make that decision. Ballistic Fab has some really nice brackets that seem to be reasonably priced, but I don't really know what I need yet.

[720Racer]

.....but I don't really know what I need yet.

Sounds like it's time to build a model!!!

[crawlin68]

Sounds like it's time to build a model!!!

Your model illustrates my confusion. I like the idea of the combo bracket that Highlander has for the frame end of the links to mount to, BUT like in your model, the upper mount for the lower links go to a crossmember which looks like it would give you better triangulation vs. being mounted out at the frame rails. Did that make any sense? So which is better?

It also look like your lower links are considerably longer than your upper links. Using the combo frame mount, it seems like your links would need to be almost the same length? I'm so confused.

[720Racer]

Your model illustrates my confusion. I like the idea of the combo bracket that Highlander has for the frame end of the links to mount to, BUT like in your model, the upper mount for the lower links go to a crossmember which looks like it would give you better triangulation vs. being mounted out at the frame rails. Did that make any sense? So which is better?

Yeah, it makes lots of sense. The two things that are hard to accomplish with the PP kit (No disrespect to Highlander) are (1) having 40* seperation between the uppers and lowers (I.E. if uppers are 18* from the frame and lowers need to be at least 22* from the frame) and (2) the length of the uppers should be between 50% and 70% of the length of the lowers.

Disclaimer: As with most other 4 link statistics, these are just things I've seen mentioned as important factors. I have no experience to back it up (yet). After I build mine I will probably be able to tell you what doesn't work well.