3/4 Link Setup and design questions

[Kbach66]

Alright...I've been working on the 3 link design on the computer for a while, and read quite a bit of books about theory, but now I'm looking for some real world offroad input. All the text I come across relate to low travel street cars, drag cars, etc. I'm curious on what areas I should be concerned about, like pinion angle throughought travel, upper/lower arm mounting points to determine roll center, articulation, etc.

It's for a X-cab fullsize chevy that's basically tube from the cab back. I'm looking for around ~30" of travel.

I've got a solidworks model of the rear that I can post once I figure out the posting dealio!

Anybody got some real world answers from first hand experience? Any comments would be greatly appreciated....I'm sick of the computer and ready to do some welding...but don't want a setup that looks good on paper, but handles like a shitbox!!

Thanks.

 

[ntsqd]

Why a 3 link and not a 4 link ? Look at the Roll Center progression of the 4 link and think about where it is relative to the CG when landing off some yump, i.e. from full droop to full bump. Done right you can get the truck to gather itself over the suspension, rather than trying to fall over, when landing all Scooby'd out.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages

 

[Kbach66]

Why wouldn't I be able to achieve similar RC movement from a 3 link? I'm not sure what type of 4 link your referring to....maybe something with both upper and lower links placed on the outboard side of the axle tubes, close to the hubs? I'm talking abou the difference between a 3 link, with a single "triangle" mounted to the frame and above the carrier(using one hiem on the housing). And a 4 link, with seperat links - each mounted to the frame, and then fairly close to each other above the carrier (using 2 hiems)

Attached (hopefully!!) is a pic of an unfinished solidworks model that I've been screwing around with. It's by no means done, so I don't need any comments on strength/integrity!!! I'm just looking for design ideas!
Thanks

 

[ntsqd]

With a 3 link the RC is fixed relative to the axle CL. With a 4 link it is not.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages

 

[ntsqd]

NFG attachment. Figures.....

OK,

3 link: RC is at the single (upper in this case) joint on the housing. It is fixed there, it can not move around. Simple and easy, but maybe you're giving up something.

4 link: These have a slightly better defined (though harder to describe in words) Roll Axis. For simplicity let's say that the lower links have a slight angle btwn them. The uppers have a pronounced angle btwn them. From the top view, extend the Line of Action (LOA) of the upper pair of links until they intersect. Do the same with the lowers. From the side view draw a line from one intersection point to the other. This is your Roll Axis (RA). Where the RA pierces a verticle plane coincident (to use a SW term) to the rear axle housing centerline is the Roll Center. Now move the whole system to full bump and look at where the RC is relative to the axle CL. Try it at full droop. Notice as you iterate the 'top view' angles btwn the pairs of link arms how the RC's position relative to the axle CL can be manipulated. All of this w/o changing the Instant Center location.

BTW, I think you'll want to turn those lower arms over. Put the shock mounting points slightly lower than the CL thru the pivot points. That way they aren't trying to twist the arm over while under load. Also, for a given weight the gusset tube will be stronger in tension than in compression.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages