I'm no engineer but I do have that sort of brain. I have learnt a few things from our own PJB and from Dan White at Suplex and I have also done a little research on my own.

It may seem strange but in the Morgan suspension when both springs are under compression the spring rate is the sum of the two spring rates. I think of it as the lower rebound spring exerting a pre-load on the upper load bearing spring. To take simple numbers (not real!!) if the upper spring has a rate of 150 lbf/in and the lower rebound spring has a rate of 100 lbf/in as long as the lower spring is under compression the total rate is 250 lbf/in. The moment the lower spring is fully extended, say when the car is cornering hard or hits a bump, the rate drops to that of the upper spring alone, that is to say (in the case of this imagined example) 150 lbf/in. This is the famous falling rate which leads to the nodding dog syndrome.

If you soften the lower spring you also soften the initial ride. Say the rate of the lower spring is reduced to 50 lbf/in the combined rate in our example is reduced to 200 lbf/in and will undoubtedly give a more comfortable ride but you will still have a falling rate when the lower spring ceases to provide that "pre-load" effect.

Obviously if the lower spring is softened and the upper spring is increased in rate the transition will be reduced (the reduction in the rate is equal to the rate of the lower spring)but the ride in the initial phases, that is over small bumps, will remain hard, if not harsh.

Ok so what happens if we select a spring that is going to give the ride we want and a length that give the desired ride height and do away with the rebound spring altogether? The result in a straight line would probable not be bad and the bounce and rebound could be controlled by a good set of dampers. Naturally some sort of rising rate system in extreme bump would be desirable, long tapered rubber bump stops or a supplementary rising rate spring could be used wink

The only problem is that to get minimum roll in cornering you would need fairly high rated springs or "sway bars".

If a fairly high rated re-bound spring that barely touches the bottom of the stub axle at static ride height is used the moment the car starts to roll the stub axle on the inside of the corner comes into contact with the rebound spring, the rate of the two springs then combines but, in this case, to limit the action of the upper spring in pushing down the unloaded wheel. The effect is to limit body roll.

These principles, in full or in part, are what all the suspension designers use. Each designer tunes the system to his requirements and those of his clients. At the end of the day it is a matter of driving style and the compromise between comfort and handling. There is only so much that can be done to tune a system that has inherent limitations.

I hope I have been clear in my layman's explanation.

For a more scientific and/or detailed explanation of the Suplex system check out Peter Ballard's discourse at Morgantica. It includes a description of the falling rate system on older Morgans: https://sites.google.com/site/morganatica/suspension/springs-progressive-rising-rate

Peter

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