My main guide to engineering is the math, but after that is my sense of engineering esthetics. And sometimes that gets in the way of finishing a design. Seriously, the single 3″ tube would have worked fine for the de Dion suspension, but a truss would weigh less and be stiffer, by a small amount on both counts. And the new truss is much simpler both to build and to mount than the previous truss of 0.5″ thinwall tubing with a plethora of tiny triangles in two planes as it is just 7, 1.5″ X 0.120 wall round tubes in a single plane. The tube diameter and wall thickness are enough to hold the toe and camber alignment while the truss is strong enough to take all the vertical and horizontal forces with a huge safety margin. The truss weighs 20 pounds with brackets, not including the filler wire from the welds. This compares to the 3″ tube which comes to exactly the same weight but not as stiff vertically. Or as pretty to look at, which as I wrote earlier is an equal criteria after weight.
I mean face it, the 3″ tube would work just fine and probably less than 3 people out of 100 would be able to feel the difference in stiffness compared to the truss. Even fewer than that would care about the looks of the truss compared to the single tube. TBH even I am just the slightest bit ambivalent about the difference in appearance between the truss and the single tube. There is the simplicity of the single tube across the back of the car, but on the other hand there is the zen-ness of the collection of triangles running across the back of the car, even if it is hidden by the bodywork for aerodynamic reasons. There is also the fact that I can lower the roll center by almost 2″ in the rear to reduce oversteer slightly with the truss. And finally there is the cost issue, a single 58″ 3″ X 0.120 wall tube is less than half the price of the 132″ of 1″ X 0.120 I would need for the truss.
And even while I’m thinking about the rear suspension I’m still thinking about the cockpit and a possible roof and side windows. Mrs. the Poet is still saying there is no way I’m going to be able to get in and out going through the top of the roll cage after climbing the side of the frame. I have zero doubts about getting in and out of my own car, if for no other reason than I will have lots of time to use the frame as exercise gear to get my upper body strength up. Or I could screw together some black pipe for a dipping rig and chinup bar and continuously build my upper body every day. 😀
And I think I need to go to bed now, and so become the Nighty Knight.