Okay more fettling, and I’m more or less there. 3 cones of 2 different specs, balancing out against the 2 Volvo mounts, and no rubber bands or bungees. By tightening and loosening the 4 bolts you can take it from what I wanted ( almost a couple inches) to zero trave (also with adjustable roll) and obviously and possibly most importantly; taking unsprung weight from fully loaded at roughly 150 kg down to maybe 30ish kg. Ive added some bump stops to the sides which also help control the roll and rebound, as does 2 of the 4 possible adjustable adjustments. The other 2 control overall travel and ride height, with shims helping out for fine adjustments.. Still needs a panhard rod. After an evenings playing around with it, I’ve got a similar response to jumping up and down in the drivers seat to what I wanted. Ie a bit like my old mini, but smaller.
So: 1 moving part, a total addition of less than 5 kilos in weight to what I started with, all the added weight being well under the axle centreline, a definitely defined roll centre, the previously mentioned sprung/unsprung weight shift, and the ability to go from spec cyclekart (no rear suspension) to full suspension just by adjusting 2 bolts. Win.
When it stops hooning it down with inclement weather I’ll roll her out of the garage and shoot a video of me jumping up and down on the drivers seat in order to demonstrably put my money where my mouth is.
Possibly the biggest unforeseen side effect is that it squeaks like dancing at a goth club when the PA cuts out….
(It’s lots of quite tightly stressed rubber parts, all squeaking away….)
Reminds me of being 21 again….