I’m at a dilemma here on the rear suspension design, so I’m asking for your help. I have narrowed down the rear suspension to 3 candidates, 2 of which are interchangeable as the major difference is method of construction, and the third would require cutting most of the back end off the car to go from either of the other two to it or from it to either of the other two.
Anyway here are the choices:
1) Reuse almost everything under the front of the minivan including the subframe. That means the struts, springs, hubs, knuckles, axles and CV joints, A-arms, and the tie rod ends. Advantages are reduced fabrication as almost everything is reused except the upper strut mount to the frame of the minivan. Major disadvantage is no way to adjust ride height except to cut the spring to make it shorter, no way to change the spring rate except to cut the spring to make it stiffer, no way to reduce roll stiffness to improve rear grip, very little way to predict the ride height, and poor camber control with body roll. Also ugly with a capital UGH! The front suspension bits of a Chrysler Town and Country are strong, but they will never win the “Rear Suspension” category of a beauty contest.
2) De Dion beam with fabricated brackets to fit the knuckles attached to a 3″ dia 0.25″ wall aluminum tube, probably a 7075 alloy. This has the main advantage of keeping the wheels pointed in mostly the right direction in all 3 axis all the time unlike option 1. It’s also much better looking than option 1, but that is faint praise from a bad comparison. Another advantage is roll stiffness can be reduced by mounting the coilovers closer to the center of the car. The major disadvantage is I can cut the pieces for the bracketry but not weld them as none of my equipment will work on the thicknesses of aluminum needed for this job and the budget does not run into buying welding equipment that will only be used for one major assembly. Secondary disadvantage is coilover shocks and springs will need to be purchased to keep the frame from dragging the ground, but that is offset with the ability to choose shock and spring rates better suited to the reduced overall weight (compared to the donor vehicle), and the ability to adjust the ride height. This will reuse the knuckle and hub along with the parts attached like brakes etc. but probably not the tie rods. Lateral location will be by a Watt’s Link mounted under the differential and connected to the hubs or the bracketry the hubs are bolted to. Fore and aft location by a parallel 4-link connecting the frame and the end bracket on the de Dion tube.
3) Bird cage style de Dion beam from thin wall small diameter steel tubing in a 3D Warren or Pratt truss that sweeps back from the knuckles to clear the transaxle while leaving room for the axle shafts to come through without hitting the structure when the suspension travels vertically. Advantages include looking cool, something I could fabricate on my own, looking cool, slightly lighter and slightly stronger than the single 3″ aluminum tube, looking cool, all the advantages of the 3″ tube version, and finally looking cool. Disadvantages are much harder to fabricate since it’s basically a space frame for the rear axle and leaves less room for the trunk and gas tank behind the engine and transaxle.
Options 2 and 3 are interchangeable, just unbolt the tube or space frame and bolt in the space frame or tube to replace, so I could make both and see which works better. Probably not going to happen because I don’t have the budget for iterative development.
Right now I’m trying to decide which of the three options I’m going with. #1 is cheapest but has the most negative compromises, #2 and #3 have similar costs but #2 is much quicker to build because there is less actual cutting and welding. So help me make up my mind
Witch on a Bicycle 