A small example has been made in order to compare the difference between helicoidal spring and leaf spring in term of stress.
This is a schematic approach on rectangular girder with an uniform load :
leaf spring version : front axle on a spring (A), rear axle on leaf spring between (C) and (E)
helicoidal spring version : front axle on a spring (A), rear axle on helicoidal spring (D)
Helicoidal and leaf springs having the same stiffness. .
Bonjour CBY, Merci pour votre réponse!
I enjoy theory, but my conclusions come from experience, very much like the people who designed the trad and the better elements in aftermarket. I am in the unusual position, for the last 30 years, of dealing with many Morgans in the community, along my own three back-to-back Plus 8s. I fit them all with identical rear suspension components, springs, shockers, bracketry.
(This is aside from the many other Morgan setups I have tried.) None of them were the same!!!!!!!!!! 
.Helicoidal and leaf springs having the same stiffness. .
That is an assumption. The moggers have never been given the spring rates of the aftermarket systems. Even the most astute, don't know them and cannot reply when asked for them. Yet even the often closed-mouthed MMC gives them out and the designers of old, like dear Peter M, could recite them on his wares in a second and tell you why and their effect.
However, let's assume the spring rates of the subject leaf and coils ARE the same for the sake of this discussion. What is missing from your analysis of the single stress point of a rear coil spring and the dual stress points of leaf springs is the flexing chassis in between, along with the rest of the car. Your punchline can only be certain for an absolutely stiff chassis, which trads have never had. Today's automobile engineers (the type with degrees and lots of physics) take a stiff chassis as a given. A flexing chassis is PART of the suspension and a very important one. It is not measured in any of the analyses I have read. It changes,
from so many factors,
from engine power/weight to driving style. It makes one-size-fits-all rules super dubious. Each trad must be individually tweaked. No way around it.
L.
