Triangulated 4 link
 

I eventually want to do a triangulated 4 link (with coilovers). I know, by reading on here, that the top bars need to be between 35 and 45 degrees. Can that be relaxed if the lower bars are at an opposite angle? I drew up an example. By no means is this to scale or correct for geometry, but it does give and example of my thought. Will this work to keep the rearend centered in a 4000lb truck on an autocross track? Any downfalls to this design?

http://i297.photobucket.com/albums/m...GBod/4Link.jpg

Also, no worries about exhaust, I plan to run outside the frame and dump in front of the wheels.

Chad

Re: Triangulated 4 link
 

I would have to do some more research, but I have not seen them done the way you illustrated.... and that's probably for a good reason!

What I would recommend, is doing a Mumford link set-up. Your lower links would converge, as pictured, and your upper links would be straight. There are multiple advantages to a mumford link, the main one having to do with the roll center. The drawback (not really IMO) is the fact that your crossmember where the lower links converge needs to be well designed and strong!

Re: Triangulated 4 link
 

What you have drawn is a double triangulated 4-link. It is popular in the rock crawler world due to the fact that it can articulate almost infinitely. It is not a good setup for street driving though, as you roll center is constantly moving, and becomes unpredictable at best. It's basically an unstable setup at speed, and in any decent cornering.

Re: Triangulated 4 link
 

Thanks Nathan and Twisted Minis, that's why they pay you guys the big bucks. It was just a thought that ran through my head. I will most likely stick to a standard triangulated setup.

Chad

Re: Triangulated 4 link
 

Nate, what you described is a Satchell Link. The Mumford Link is an alternative to the Watts Link for maintaining center.

Mumford:
http://www.not2fast.com/chassis/mumford_mallock.jpg

http://www.not2fast.com/chassis/mumf...formanceS1.jpg

Satchell:
http://www.vpmcobras.com/images/satchell1.jpg

http://www.vpmcobras.com/images/satchell3.jpg

The reason you don't see more Satchell setups is because it is hard to package into most frames, but worth it if you can.

Re: Triangulated 4 link
 

That's what I meant to type!:uhmk: Too many suspension configurations on the mind!

Thanks for clarifying!

Now the Mumford link IS pretty cool!:ito:

Re: Triangulated 4 link
 

:lol: I figured that was the case ;)

Re: Triangulated 4 link
 

ya im going to do the satchell link on my frame... you get a lower Instant center with it if i remember correctly?

Re: Triangulated 4 link
 

That Satchell link is on a Jaguar isn't it?

Re: Triangulated 4 link
 

I just got hold of a Ford 9" rear end that I believe is from a mid 70's Torino or T-Bird and it has brackets for a very similar 4 link setup. Both sets of arms were angled with the lowers converging towards the front. I dont know whether these cars suffered from excessive articulation or not.

Re: Triangulated 4 link
 

Actually i tell a lie - now that I look at the brackets I cut off the housing I see that the top links converge towards the front and the rears go out presumably to the frame. The lower bars are set way to the outer ends of the housing angled outwards. here's a pic http://i6.photobucket.com/albums/y23...9inch_rear.jpg

this is upside down BTW.
Nate; why does the satchell link have an advantage over a triangulated 4 with the angled bars on top? My plans for this rear end is to use a triangulated 4 with the top bars diverging out forwards from central mounts welded on top of the pumpkin and the lower arms outside the frame. It seems that the satchell configuration would be harder to get the 45* angles on the lower bars with the frame there.
Not meaning to hijack the threat BTW; I just thought it was interesting to see this configuration right after i picked up this rear end with a similar layout.
-Andy

Re: Triangulated 4 link
 

You're not hijacking at all. I am interested too.

Chad

Re: Triangulated 4 link
 

The Satchell link provides a lower roll center.

I have actually found it to be easier to achieve 45 degrees on each bar with a Satchell link, because the bars can run under the frame. I generally set them wider than the frame, as close to the wheel as I can get them. On one I did it was possible to go past 45 degrees, so I pulled the bushing in towards the pumpkin a bit.

On a Satchell link it is always important to set the lower bars up so that the bushings are wide on the axle and narrow on the frame, like the pictures above. Also your lower bars should be a bit more heavy duty than a standard bar, since the lower bar sees more force applied to it. And when that bar is at an angle, it tries to make the center of the bar flex under power. I generally either step up the size of the tube slightly, with the same wall thickness, or run the same tube size with a slightly thicker wall.

Also the upper bars are generally angle out a few degrees (2-3) to achieve some under steer.

Re: Triangulated 4 link
 

lower roll center than what? the arrangement with the triangulated bars on top?
When you talk about angling out the top bars slightly where are you setting them? inside the frame like this:
http://i6.photobucket.com/albums/y23...top_inside.jpg
or outside like this:
http://i6.photobucket.com/albums/y23...op_outside.jpg

Apologies for my crude renderings but I was halfway through making a 3d version of my Apache frame and the new rearend so I threw in the simple bars to try out the different arrangements. Blue bars are uppers, reds are lowers. I havent done any moutning points as yet, this is still early stuff.
Putting the lowers under the frame seems like it would make problems with ground clearance, at least on this frame layout. I laid out the lower bars to sit inside the step notch, is that far enough apart on the axle or do they need to be further out?
http://i6.photobucket.com/albums/y23...hell_persp.jpg

At 5" ride height, with a 30" tire and the bars parallel to the ground I have this: http://i6.photobucket.com/albums/y23...chell_side.jpg
It actually looks like this might be easier to package than the triangulated 4 I'd been thinking of here: http://i6.photobucket.com/albums/y23...i4_persp01.jpg
Attaching the top bars to the pumpkin moves them up so high I'd not be sure how to attach them without some huge high X member and I wouldnt want to have them facing down towards the front would I? Moving them down the pumpkin makes them short and I'm not sure how that would function. I've seen it done.
http://i6.photobucket.com/albums/y23...tri4_top01.jpg
I guess there's not much in it at first glance but will the satchell outperform the tri-4 in other ways besides the roll center?

-Andy

Re: Triangulated 4 link
 

Yes lower roll center than with the upper bars triangulated.

For the upper bars, being on the inside or outside of the frame doesn't matter much.

However you don't want both of your upper and lower bars parallel to the ground. With a Satchell link, I set the uppers parallel to the ground at ride height, with the lowers angle up slightly at that same height. This has to do with your Instant Center.

A Satchell link won't really make a huge difference over a standard 4-link set up the same way. But it would be better than the setup you have illustrated above. But only for one simple reason. With the bars being narrow on the axle, it puts your roll center on the axle. Which means it moves in relation to the vehicle. So your vehicle will feel different at ride height, versus anything else. Where if the bars triangulate on the frame, your roll center is always consistent. Most people don't care enough about handling to be concerned with this though, as it isn't a vast difference.

Re: Triangulated 4 link
 

So just reversing the triangulated bars will improve the tri-4 setup? Interesting. That makes the two setups even more similar with the only real difference being whether the angled bars live above or below the axle. Putting them wide on the axle also reduces my options for bag placement and shock moutning.
I havent worked out any of the angles on the bars in the side views as yet. im not really sure where to assume the CoG should be. These renders are just quick and dirty 3d sketches - i just threw these bars in here since I had your attention. I've been putting off doing this for a while so it was good to jump in and start it.
On the satchell setup I have here, are the angled bars out towards the axele ends far enough do you think?
If so the main concern seems to be how to package the cross member for them to attach at the front and how I keep them away from the driveshaft.
I'd been kind of planning to get a tri4 setup from Suicide doors to make it a little easier but if I do the satchell i guess im starting from scratch.

Thanks

-Andy

Re: Triangulated 4 link
 

To keep them away from the driveshaft I would keep the same angle on the bar, and just move the bar closer to the wheel so that there is some space in between the bars to provide more driveline clearance.

Re: Triangulated 4 link
 

Like this?
http://i6.photobucket.com/albums/y23...chell2_top.jpg

I nudged the notch forward to give more room for the lower bars to slip inside and moved them out a couple inches. I also angled them up towards the front 8degrees:
http://i6.photobucket.com/albums/y23...hell2_side.jpg

Im going to need a big old driveshaft hoop I think:
http://i6.photobucket.com/albums/y23...ell2_persp.jpg

The offest pinion on the 9 inch is a wrinkle in this. i moved the pumpkin sideways to centre the pinion and when I shorten the housing I could offset it to compensate.

-A

Re: Triangulated 4 link
 

That is basically what I was saying. Your lower bars should still be the longer of the bars in this situation however.

The pinion is offset in the chassis for a reason. That could have built it centered from the factory if they wanted to. Having it offset keeps a constant angle on the U-joints, which keeps them loaded and helps them last.

Re: Triangulated 4 link
 

keeping it offset is going to make locating those angled bars tricky though isn't it?
the lower bars are currently about 17" long. is that long enough and is there a relationship between that length and how long the uppers should be? I seem to remember reading somewhere there was a ratio of the short to the long bars in a four link but I cant find it right now. Im looking at Adam's "chassis engineering" book at his section on the satchell and his diagram has the lower arms at less than 45 degrees off the center line and longer than mine.

Re: Triangulated 4 link
 

Generally the upper bar should be 70-80% of the length of the lower bars.

I don't think you should have an issue locating the bars. If you make them longer, the driveshaft will be offset less in relation to the bars, just because of distance. I can't post pictures right now, but I did it on a minitruck with a more sever offset because of the short length and 2 piece driveshaft, and it had I believe 22-24" long lower bars.

Re: Triangulated 4 link
 

really? i have read a few (slightly mind bending ) threads over on corner carvers where the opinion seems to favor the longer upper bars to control the Roll center position . They touch on it but dont really get to the bottom of it in this thread between posts 103 and 115 or so: http://corner-carvers.com/forums/sho...atchell&page=3
this is the thread where the pics from the top of the thread come from and yes, its a Jag.

i've seen the opposite stressed elsewhere however like here http://www.pro-touring.com/forum/arc...p/t-21677.html

I really need to run my numbers through some performance analyzer before i go much further. The link above on Pro touring has bar lengths of 21" upper and 28 or so lower which is right at 75% isn't it so that is right in the range you advise.

So you think i should keep the pinion offset to the side and shuffle bar mounting points around the offset driveshaft loop? i'll have to have another play in the 3D model and see what i come up with.
Thank you so much for your advice BTW, I totally appreciate it.

-Andy

Re: Triangulated 4 link
 

Well, suspension design is one of those great things, where there are a few things known to work, and many theories believed to work. I don't agree with the longer upper arms to set roll center on a Satchell link, because your lower bars are actually setting your roll center. The only thing your upper arms are doing, that their length and angle is concerned about, is tuning roll steer. Which by angling them slightly out on a Satchell link, you will have under control.

I think 21 and 28" bars sound reasonable. I do think you should keep the driveshaft offset.

Here is the one I did, the driveshaft was offset and I just spaced the bars out evenly. So one bushing was close to the driveshaft at full lift, and the other was about 2-3 inches away.
http://www.streetsource.com/uploads/...916PM60731.jpg
http://www.streetsource.com/uploads/...430AM38141.jpg
http://www.streetsource.com/uploads/...1836PM4081.jpg
http://www.streetsource.com/uploads/...121PM98591.jpg

Re: Triangulated 4 link
 

oh cool, thanks for the pics. Those lower bars are much slimmer than I expected. Are those adjustable ends at the rear of them?
What are those turnbuckle fulcrum things tied to the bridge and the front of the pumpkin? are you fixing the pinion angle there?
I guess the posts I linked were discussing the long bars for reducing the amount the roll center migrates during travel but I think those other bar numbers that prove your point came from running the numbers through a suspension analyzer.
I already think hat when i lengthen those lower bars and offset the rear end again Im going to run into interference between the lower bars and the front of the notch unless I lengthen the notch like the one you have in your pics.
How did this one ride and handle when it was done?

-Andy

Re: Triangulated 4 link
 

Those brackets hold the limiting straps. The truck was built to 3-wheel, so that is my version of a "chain bridge" which is big in the lowrider world. They generally use chains though, and I thought that would be too noisy.

The lower bars are 1.25" .188 wall tube. They are pretty stout. But again it is on a minitruck, with about 80 horsepower. It rode great for the short trip it saw before being torn down to be "finished". It's still torn apart in his garage.


Can you just run a longer lower tab to get the bar down away from the frame a bit more? I know on these trucks the frame kicks up a bit before exiting behind the cab. I would think the bars could be go under there.

I've done more backhalfs than notches, so I generally build the frame to suit my 4-link needs.