5 link rear end

[Jet]

Hi trojan hows things?

Mr Boost, Its very possible to bottom out suspension, the cars that spend $10,000+ in each corner on shocks bottom out, its why they run bump stops. its hard to find the medium between smooth enough to hit ruff at fast, and hard enough to take massive jumps, most of the time you need both, enternal bypass shocks help alot for this, but you still bottom your suspension out, thats why its designed for the supension to be bottomed out with the frame off the ground, rather than the frame hitting the ground and becoming a solid conection with earth, which can hurt alot the tires now take the force, its still ruff, but it saves alot. bump stops are bassically a massively high in pressure air shock which take alot of force to move, they are well known for saving suspension after a huge jump because it removes the shock loading of bottoming out. Your also not using your shocks full potentinal if the frame hits the ground before it bottoms out. The reason the barracuda doesn't do this is because the springs are so tight due to the buggy being setup for rally type driving etc its VERY hard to bottom out both shocks enough to fit the frame on the ground, and the extra travel can be used to soak up a jump that has gone wrong etc. Guys, i know everyones views and opinions on this allready and i dont want another debate about it! thats just my view and im running with it for now. As you've read earlyer my next build will be bottoming out before the frame hits.

Cheers
Phil

[Boostinjdm]

Most of what you said makes sense. Except bottoming out a shock is not using it's "full potential",  it's using it's full stroke they are not the same thing.  I will leave it at that.

How are you coming on your five link?

[Jet]

I mean bottoming the frame out, with out the shock bottoming sorry my bad.

Nice and slow, Whats so bad about 6 link? seems a shit load stronger?

[fabr]

Completely unnecessary. More expense.

[Admin]

Boost, My buddy has a few old spare electric wheel chairs, Let me know if you will need one... Bottoming the shocks then puts the load into the tire...Jet if you wish anything moved just let us know...

[fabr]

[Engineer]

IMO all of these designs achieve what so many do not.The pivots are as close as possible to the wheel . Only makes sense to me that that is the best design objective. I don't understand how some "respected" builders don't get that. Personally I like that last one based on a midboard hub and TA plate that comes with it..

Fabr, your correct, that means longer axle, longer axle means more travel! travel doesn't bother me, but the old mans a bit of a pussy so we need to make it nice and smooth 

Nah, Im aiming for 20" all round REAL travel. its something like 26 all round if you let the wheel go past the frame, if anybody has seen the last issue of dirtcomp you will see why im shit scared of it going past the frame.

question for you all.

In the centre im designing up i can get the cv's as close to each other as i like, that means longer axle, more travel etc. etc. But how close can i put them? sure i can bolt them sidebyside but the plunge is going to rip enough each other. so what can i do? i have it set at 2inch's between the cv's, i would love them to be as close as possible.

Cheers
Phil

I agree with fabr, that nothing is more disgusting than a rear design with the CV 6-10 inches inboard of the wheel.  One reason for it is the "minimum offset" wheels that are so common because people can't seem to measure and get what they need or find available what they need.  Also the VW beginings of the hobby dictated these type of wheels.  Rant over.

That all being said, I don't believe mounting the end of the A-arm or 5-link pivots closer to the wheel necessarily helps anything.  If you think about plunge on a 5-link or A-arm design, the main cause of plunge is that the A-arms are different in length, than the CV spacing.  I am currently designing around the F-150 CV's that have zero plunge in the stars.  There is a point in the CV that the star rotates around.  The same as in a 930.  The distance between the rotation point of the inner and outer CV is the needed length of the A-arm's or 5-link bars from hiem center to hiem center if you want to reduce plunge.

In the picture below the red line shows the length from CV center to center.  The blue lines show the pivot axises.  The pivots are almost in line with the CV centers.  This setup is going to have very little plunge.



Now plunge is not necessarily a bad thing altogether.  Some may be good to keep the CV from always running on the exact same surface.  I just don't understand how plunge is a mystery.

So on the car pictured, I don't believe that making the 5 link mounts on the outer carrier closer to the wheel whould help anything , but it would definately increase plunge.

I try to increase axle length.  Like Jet said longer axles = more travel.  Because the CV angle's limit the travel, and the A-arm or 5-link pivots don't, I think the axle is the first consideration.  More compact outer hubs help greatly along with a narrower width in the center.  Once the axle length is decided, then you can look at the A-arm or 5-link mounting possibility's.  But increasing A-arm length beyond axle length will only result in more plunge.

Also the A-arm pivots don't have to be inline with the CV center to reduce plunge.  But the arc lengths should be similar.  If the A-arm mounts in the center are 2" outboard of the CV center, then placing the outer A-arm mounts 2" outboard of the CV center, would make for minimal plunge.

Unequal length arms for Camber purposes are going to make it more interesting, but the problem is the same as finding an ideal tie rod length and location for the front.

So to answer Jet's question, IMO make the center as narrow as possible, then see if you can get the suspension mounts in a position that give's an allowable amount of plunge.

[fabr]

yep.

[Jet]

Hi Engineer, thanks for the responce!

I've got the cv's 20mm apart, thats just under 1 inch. I'll locate the axel in the cv's and allow the plunge that will happen, to occur on the outside.

This means that  centre is very thin, infact i've consitered running the suspension mounts straight up next to each other, on one tube, or two tubes butted up next to each other, or an oval tube. whats the down side to doing this?
this way the plunge that is created by what im about to say below is helped to over come. the sprocket and disc will sit between the suspension arms.

Also on the outside i'll be running the cv fairly much right up next to the wheel hub, and the wheels will be offset as far in as possible. so the connections may be inwards a bit, which creates plunge, i'll keep plunge down to a small amount tho.
All this is allowing 40inch long axels either side which gives about 22" of real travel, i think its something like 32" if you max the cv's and let the wheels come past the frame?
What length axles do you use?
Does anybody have drawings of the outer upright?
i would like to draw this up just so i can use the concept on a drawing so i can design the frame, i'll be using a diffrent 5 link rear end when the time comes to it due to 1 off costs!

[Engineer]

Hello Jet!

I will post a diagram and a drawing of an old 5-link design for reference.





I am not quite following some of what your saying, so I will ask a couple questions.

I've got the cv's 20mm apart, thats just under 1 inch. I'll locate the axel in the cv's and allow the plunge that will happen, to occur on the outside.

That is narrow!  Are the CV's plunging or non-plunging type?

This means that  centre is very thin, infact i've consitered running the suspension mounts straight up next to each other, on one tube, or two tubes butted up next to each other, or an oval tube. whats the down side to doing this?
this way the plunge that is created by what im about to say below is helped to over come. the sprocket and disc will sit between the suspension arms.

I have never been able to figure a way to get the inner mounts that close.  I think strength of the suspension mounting would be a concern with only one tube.  Make it a big one. 

What do you mean by between?  I take it to mean that either the mounts are above/below the sprocket, or in front of and behind.  If you intend for the mounts on the outboard side to be inside the wheel, then the separation distance will be limited.

If you mean in front of or behind, then remember that the the 3 links running sideways (as seen from above) must be parrallel, or as the suspension move up and down you will get toe changes because of the arc that the front two links follow.

I need a diagram! 

Also on the outside i'll be running the cv fairly much right up next to the wheel hub, and the wheels will be offset as far in as possible. so the connections may be inwards a bit, which creates plunge, i'll keep plunge down to a small amount tho.

So you will use something like a midboard hub?

http://www.gear-one.com/Htmls/centerboards.html

The 5-link connections may be inside the inner edge of the wheel?  May work for the side rods, but the fore and aft connections will have to be outside the wheel and give clearance for the tire sidewall.  Also the shock connection will need to be outside the wheel, unless you are planning to put it on a link in order to get some ratio.

All this is allowing 40inch long axels either side which gives about 22" of real travel, i think its something like 32" if you max the cv's and let the wheels come past the frame?
What length axles do you use?
Does anybody have drawings of the outer upright?
i would like to draw this up just so i can use the concept on a drawing so i can design the frame, i'll be using a diffrent 5 link rear end when the time comes to it due to 1 off costs!

I have had trouble locating axles that long.  My drawing above shows 28" axles, the longest I could find with out special order.  I am showing 20" of travel with 3" of frame clearance at bottom.  The CV's that I am using are non-plunging and will go 44 degrees, but I do not plan to push them nearly that far.  Any travel that has the frame in contact with the ground is IMO not worth discussing.

The 28" axles work for me because I am getting the travel I want, and with the off the shelf bearings and CV's, I come up with close to the track width I was looking for.  If I could find inexpensive 30-32" axles I may have gone a bit wider, or tried to narrow up something more to make room.

I don't really have a complete drawing of the upright, because I keep changing it.  I just can't  seem to get it to meet all of the criteria that I am looking for.  Mainly simplicity!

I would like to see a sketch of how you plan to run the bearings/sprockets/CV's in the mid.  It sounds like you have an interesting plan.

[Rick S.]

Another advantage to zero plunge is that you can run the cv housings outboard on the axles.
This will allow a little more angle before the shaft fouls on the boot flange.
You not only get increased angle, but the cv's are actually climbing higher on the axles as you ride them farther outboard. I like to set them up this way because now you're limiting the side to side play of the axle. A set up with zero plunge that allows the axle to drift all over is not good IMO.

[fabr]

With the non plunging cv's at big angles.How well does the boot hold up running at high speed with the big angle? Engineer I'm assuming you are not designing to normally run at big angles but many seem to do so and I'm wondering if boot failure is an issue with them?

[Admin]

My cvs are non plunging and i have found some boots that are very flexible and have held up extremely well, About the only thing that wrecks my boots is a sharp rock or something threw from the front tire...

[Doug Heim]

Yes I am about to say somthing most of you would not expect but...

Edge Products sells a set of really nice heavy duty boots for 930 CVs. Thsy have them custom made and are 2-3 times the wall thickness as standard boots. They currently have them in the clearance section. If anyone buys a set let me know. I want a set too. We can combine for shipping. They attach to the outer cage so no issues with axle angle being effected.

[Jet]

apart from my current buggy, which runs a special type of boot, i wouldn't go past the edge boot. Tony had them custom made and they are perfect. It wont be long untill they go mainstream for Racing across australia. There just not going to break!