A small exemple 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.
Girder length 4,5m
wheight : 450 daN
This quite the same configuration on a Morgan except the girder is not regular and straight.

[Linked Image]


Values of Von Mises constraints (daN/mm²) :
Helicoidal spring / / leaf spring
A 0,2 // 0,2
B 7,71 / / 7,71
C 1,93 / / 2,56 (linkage)
D 3,00 (linkage) / / 1,97
E 0,75 / / 0,75 (linkage)
F 0 / / 0

The maximum constraint around the rear spring :
leaf spring : 2,56 daN/mm² at the front linkage (C)
helicoidal spring : 3 daN/mm² at the spring linkage (D)
A difference of 17 %, not a large amount given that the security coefficient for a chassis is generally around 3 and 4 (300 % - 400%) . The spreading of the forces is only between the 2 linkages of the leaf spring.
There is no difference for the front and rear parts . In terms of stress analysis the girder sections sees the same force moment.

Regards
2005 PLUS 4