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Twist on 3/4 eliptic -- theory

thedrip

thedrip

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I had this bright idea tonight, thinking about changing up the rear suspension on my Trazer. First was inboarding the springs, then inboard and 3/4 eliptic. Now I've thought of a twist on the normal 3/4 implementation, and was wondering if anyone had ever seen it done this way, or if it really makes any sense at all.

In a normal 3/4 eliptic, the upper leaf is a single leaf, shackled to the main leaf pack. The upper leaf lays flat against the frame (or whatever bracketry is there), and the spring eye is static relative to the frame. When the axle is unloaded, the upper spring falls away from the frame, allowing much more droop than a regular leaf setup.

My twist is this. The upper leaf is a multi leaf pack. Similar to a 1/4 eliptic pack. Bolted to the frame like a normal 3/4 setup. With the multi leaf pack, the upper pack would maintain an arch at ride height. With the upper and lower packs both fighting compression, effective spring rate would be greatly reduced. Assuming the 1/4 pack and main pack have the same rate, then the effective rate would be 1/2 of that. When the upper leaf pack "bottoms" against the frame, the lower leaf could still compress, but then the suspension would have a higher effective spring rate. This would mean a softer spring rate until the suspension is part way through the compression cycle, then the spring rate would increase, like a real poor man's air bump.

On the other side of suspension cycling, during droop/unloading, the multileaf 3/4 setup should behave differently as well. A regular 3/4 setup has excessive droop, requiring a center limit strap in most applications. The multileaf upper would have much greater resistance to droop, allowing more droop than a regular leaf setup, but preventing the "unloading" commonly associated with a 3/4 setup.

These are just crazy ramblings going on in my head, and if any of it seems illogical, incorrect, or insane, please explain to me why. I'm actually considering trying this as a setup to see how it works, unless someone has done it before and it's just a bad idea.

Thanks for reading all of that, if you can. I might even draw this out later to help everyone understand my poor explanations =) I'm hoping this gets enough discussion to warrant being moved to the CoG forum. That is if I'm not just really stupid in thinking this up.

suspidea.jpg
 
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By tuning not only the overall spring rate, but the rates of the upper vs lower pack, it seems you would be able to control how much travel would happen before the upper pack flattened out, and the rate increase happened. Also you would be able to choose what the combined rate, and the rate after the change would be. This is getting better and better looking, and I'm going crazier and crazier!
 
It seems after talking with a local guy, that I'm not crazy, this works. Its also just a regular old 3/4 elliptic. What I'm used to seeing, and is also called 3/4 is a buggy leaf setup, which has the single leaf attached to the frame.
 
I would build a way to lock the shackle in the up position. That way if it handles poorly on the street it can be pinned up, then later on the trail have the pin removed for full droop.
 
If the upper 1/2 leaf and the lower full leaf have similar dimensions (from the springpin back) I doubt you'd even need that rear shackle. There won't be any disparity between the lengths of those spring packs as they flatten out.

Simpler is better.



You realize of course that you are about to re-start the age old arguement about whether a drooping tire with no weight on it has any real benefit. :D
 
A drooping tire with no weight... I do not believe that there is such a thing. There is always the weight of the rim, tire, and a portion of the axle housing. I think that ANY traction is better than NO traction.
 
How effective would that really be? If both axles are locked then how much flex becomes unnecessary? I'm not so worried about hanging a tire in the the air as I am about moving forward.

now if you were doing a 1/4 elliptical setup then at least you would be gaining departure angle.
 
I have a friend with a j$$p with this same setup as well as the pin setup earlier mentioned. He is locked front and rear and within the 2 years Ive been wheeling with him Ive only seen him unpin it for a RTI ramp competition. He says thats the ony time he has ever needed it.
 
blazd88 said:
I have a friend with a j$$p with this same setup as well as the pin setup earlier mentioned. He is locked front and rear and within the 2 years Ive been wheeling with him Ive only seen him unpin it for a RTI ramp competition. He says thats the ony time he has ever needed it.
Click to expand...

what kind of numbers did he get on the ramp? any pics?
 
Blazdd88
This wouldnt happen to be a older jeep with flames on 38's from Luffkin,Tx thats been beat to death would iT?
 
No, but I know who your talking about. Dont remeber his score exactly but lets just say he pissed of a few linked big tired guys. As far as pics I dont have any of it flexed but Ill see what I got.
 
This is the only one I could find for now. It looks simple but a 400+ hp 351, a C-6 and an Atlas 2 help it quite a bit.(for a heep lol) The side says Hammerwagon if that helps.
IMG_0948_sized.jpg
 
Marv actually had the Springer Rear suspension & a buggy leaf on the front suspension.

Harley
 
theres a toy guy on pirate roc doc that used i think 2 leaves in the upper pack. he said it helped alot kept it from being unpredictable and have alot of sway. i think it would flex more also with there being some uptravel in the top pack.
im thinking about doing it on my toyota as well
 
thedrip said:
major snippage.......
....This would mean a softer spring rate until the suspension is part way through the compression cycle, then the spring rate would increase, like a real poor man's air bump.
Click to expand...
No, it wouldn't. True, you would get a major ramping-up in spring rate in compression, which could be a good thing. The problem is that unless you're running by-pass shocks tuned to have a huge rebound damping rate in the range of the upper spring's compression you will have what the LocosMocos call a "Dawg Launcher." I think that's suitably descriptive. :wink1:

So-called "Air Bumps" (which are really more hydraulic than air or nitrogen) have shim stack damping in both compression and rebound. The rebound stack is monster stiff so that the bump does NOT act like a spring.
 
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