Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing The Trad Supension Basic

I cannot agree. But after I explain why, I think that someone with your acumen will understand.

ALL cars today are built on rigid frames..Morgan went to considerable lengths and added millions in cost with the Aero and CX lines to achieve that.

Yet everything else they have made from 1909 to 2019 had a flexing frame, which used to be a characteristic of vintage cars. As a frame flexes, it becomes,an important part of the suspension, the handling, the car's elan. It immediately charms every new driving or dismays them if the car has not been sorted properly. The frame is affected by all sorts of things, from the way they stack them at the Factory, to the equipment it is finally fit with, to how it is stored and by driver's style over time. After a short time, no two trads are alike or even as it was a decade ago. Each has to be fettled individually and continually.

When it is tweaked perfectly, a trad is deliciously sensuous, an experience that cannot be duplicated by modern vehicles. Sadly, most designers and after-marketeers these days have been trained to design for stiff frame vehicles. That allows to wrongly promise that one size fits all.

One example is the rear suspension we are speaking of. One should avoid focusing forces at a single point with a vehicle with a flexing frame. It is infinitely wiser to spread those forces along the frame with a fine set of leaf springs. As you suggested, leaf springs are capable of far greater sophistication and design than coil springs. Problem is, coils springs took over the industry. That is why I am interested in BBC. Not because of his "anti-tramp" leaf springs but because of his enthusiasm and quality

L.

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.




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.

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!!!!!!!!!! .


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.

"Helicoidal and leaf springs having the same stiffness" This is only an assumption for this small exemple showing that the spreading of the forces concern only the section between the 2 linkages of the leaf spring.
For this exemple you can choose a girder with an oversized section or a small section or different sections between the 2 linkage of the leaf spring, the conclusion is the same, there is a difference around 20 % between the 2 configurations.

Yes Morgan trads have a flexible chassis, mostly in torsion due to the ladder configuration. In pure bending this is not a today car, but...

"A flexing chassis is PART of the suspension and a very important one " … perhaps in the case of Morgan with their short suspension travels, but the chassis acts like a massive rate spring and don't have itself any internal dampering. Imagine a nude chassis fixed on a bench, you bend it or distor it and you suddently release it. What append ? In fact you add a massive spring over the suspensions with a non negligible travel if your chassis is very flexible.

Except for the trucks which have very rigid ladder chassis, at the moment all the cars have a rigid chassis : touring, rally, Formula 1 etc. and have tuned suspensions for their purpose improving the driving.
.
Some years ago I modelised the chassis of my PLUS 4, I was curious to verify the MORGAN chassis legend. I am a normal driver, not a pilot and I like sciences, so I use stress analysis program, this is less dangerous than extreme driving and keeps exercising my mind.
Stress analysis on the main girder gives an idea of the constraint values. The most critical part begins at motor & door level. Under a 3g vertical impact the constraint is roughly 12 daN/mm² (~3,82*3) inducing a security coefficient of roughtly 3 (depending on the used steel).

I love my MOG, and use it for touring, with speed limitatios you can keep driving sensations we can all share, but each with his own methods. Experience is the final complement of the theorie.

Yes CBY, I understood that. But it is quite an assumption for real life and I wanted that to be clear. And the newer aftermarket, when using coil springs, do not reveal their spring rates as the older aftermarket and the Factory once did.


Yes. Then you can draw conclusions. But they would not apply to trads that do not use girders or have a stiff chassis like all modern fare. They use a light flexing frame, typical of the Golden Age of Automobiles in the 1920s and 30s. . The flex is part of the suspension and imparts a delicious feel when set up properly. Something I have never experienced in other autos. And a dual point spring system is best as it spreads the stress over two points on each side rather than focusing them on two. The problem of focusing suspension or other forces always causes problems to Morgan trads. Even the mighty crossframe at the front bends like a bow with braking forces For decades, moggers banged thee old kingpins down the tubes to prevent that. https://www.gomog.com/allmorgan/CrossframeBrakingEffect.jpg When the Factory tried to copy the Mulberry anti-tramp bars to cure early Roadster tramp, (they used one anti-tramp bar only to keep costs down) their fitting point sheared!. I could go on with examples forever. Leafs springs (bless'em) work for decades on the Morgan trad chassis. They also USE the flexing frame rather than ignoring it.




Absolutely. Not a "today car" at all. Applying standard suspension principles that have been used and taught for the last 50 years is inherently unwise. However, I do understand that experts taught in ways and means of another era, think they are designing properly. A good question to you would be to ask yourself why leaf springs are the goto technology in the long distance tricking arena. [b]Think of a standard 36m trailer for example. What does it share with a trad Morgan?[/b] They certainly do NOT have a stiff frame. Ever seen one that went off the road?

You mean like my UK chassis below?



Morgan trad chassis are not made of memory steel or anything better than simple mild steel railing. Material cost is about 400 quid. In the case you describe, they will bend and stay that way. But they will still remain flexible. It is why I advise anyone making or buying a chassis (aside from G.E.E.) to ship their chassis directly to a chassis straightener shop, and spend a few quid to have it straightened. But it is going to change anyway depending on equipment and usage. But it will make assembly a lot less frustrating. I deal with this daily on the Help Line.



[quote=CBY] Some years ago I modelized the chassis of my PLUS 4, I was curious to verify the MORGAN chassis legend. I am a normal driver, not a pilot and I like sciences, so I use stress analysis program, this is less dangerous than extreme driving and keeps exercising my mind. Stress analysis on the main girder gives an idea of the constraint values. The most critical part begins at motor & door level. Under a 3g vertical impact the constraint is roughly 12 daN/mm² (~3,82*3) inducing a security coefficient of roughly 3 (depending on the used steel).

I come from a non-mechanical background as well. From a more cerebral training and profession. I prefer Morgans. They have been my hobby for 30 years, either working on them or mogging in them. I retired very young and have studied and experienced Morgans more than all scholastic studies. I was soon assured by everyone working on them, that each one is different, for the reasons I have given and other stuff. Accordingly, I don't think Morgans are susceptible to formulas, especially another technological era based on stiff chassis era. Hell, that era even reduced the automobile tyre air cushions. Not everything, in any era, makes sense. One has to progress by trial and error.

[quote=CBY]I love my MOG, and use it for touring, with speed limitations you can keep driving sensations we can all share, but each with his own methods. Experience is the final complement of the theory.

Me too. I muse now about the last 25 years whether Morgans and the aftermarket has changed so much because the newer decision makers were trained to expect a one-size-fits-all car. Stiff chassis, like the Aeros and the CX cars.. They cannot not fathom a flexing chassis. (who can blame them?!!) People from Aston Martin or Ferrari or those who read modern car magazines worship stiff chassis. But any trad owner will tell you how he/she adores the feeling of his trad when it is set right, and on the right road. My wife wouldn't let me sell it even if I wanted to. I have agreed with that on the condition that HW + Battery<MW

I do not apply this thinking to the non-Morgan components trads use. In my case, I choose what is best from the buffet available for my, for example, engine. 1960 to 2004 and the aftermarket.

Thank you for the link. It seems to show the advisability of leaf springs on trads.

Lorne

Few clarification :
.for material resistance, stress analysis, the term "girder" or "beam" designates a long part whose dimensions of its section are smaller.
A gider can have sections like L, T, H, I, square, rectangle, round etc. .. or Z like on the Morgan.

"In the case you describe, they will bend and stay that way. But they will still remain flexible "
. In term of resistance a steel is characterized by :
Re : Elastic limit
Rr : Rupture limit
Below the Elastic limit, the material can bend under a force and return to its initial position when the force is released. It is in the elastic domain. Applying a force ahead you distort the material, by instance to transform a plate to a Z girder. If you continue to apply the force and you reach the rupture limit, you break the material.
Calculation of structure take into account the Elastic limit with a security coefficient in order to don't exceed the Elastic limit in order to remain in the elastic domain.
I don't know the steel used by MORGAN, but generaly steel with a Re above 30 daN/mm² is used… I hope.

"I don't think Morgans are susceptible to formulas"… Why not ? I hope Newton, Young and others are deaf and are not rolling in their grave!

I think the 'susceptible to formulas' thing is just a way of expressing that, with the cars being hand made with quite large tolerances (by robot standards) and with wide variarions of material over the years, the flexible chassis, interaction of the wood frame/body panels and the suspension itself result in a system with so many variables that you'd need calculations for every car individually.

K

No clue. Such things are not revealed by the MMC and frankly, I don't think anyone, even those there, ever asked. They used whatever was used from the time they began using such frames..in 1936. As for parts, my old little village in Quebec had three machine shops. They would all roll their eyes when I would bring them broken metal pieces [b]though they adored Morgans, a village machine shop's dream of a machine. [/b]

In the first few years of mogging, I would wait weeks for MMC replacement parts to arrive. But I learned my first gomog law. Namely, that the only thing I knew about a failed machine part is that it will fail again if replaced from the same original source. As I have always lived in cultures (Canada and SA) that, for one reason or another, legally permit parts to be copied, repaired, improved, I took that route with permanent success and no repeats.distress. Here is merely one example. https://www.gomog.com/allmorgan/RPplate2.jpg The later MMC plate that holds the wheels to the steering rack broke into pieces, happily at the very end of a 962 km high speed day from Sault-Saint-Marie to our former home in Quebec.


You misunderstood, dear CBY. I am sure each trad is susceptible to formulas individually. But as each have a different non-quantifiable element (chassis flex) from the start, one that is constantly changing over time depending on many individual influences, how can a forumula be used? And even if, by some miracle, we had that input, it would apply to a single Morgan. The result for all trads would merely be unknown result with unknown long term effects?!! Unlike anything I have experienced in any other vehicle type but one. At the time, my perception of suspension had been formed by hi-performance snowmobiles, all of which have owner adjustable suspension parts and around 150 different setups to match each vehicle and owner style. Were you aware that 70 years ago, the MMC suggested an option of adjustable rear suspension dampening controllable by the driver while driving?

You must blame my wife for all this. Decades ago when I arrived at home with our first Morgan, she was extremely excited. However, after a short first ride with me, she got out of the car with a two word opinion" FIX IT!", accompanied by an angry glare as if I had invented the car. So I had no choice. Happily, I have found that, with obvious and sufficient owner input, trads can be simply and individually tweaked until their suspensions are downright delicious. Don't have to change much aside from making sure everything is functioning as it original designers intended.

Thank you K. YOU GOT IT! However, there was not much variation in basic materials I can recall. Though after control of such decisions changed, by the 1990s, many more parts were being outsourced and/or suppliers and the designs were changed. For example, the wheels (tyres and rims) came to contain more metal than air or superform wings, long door cars, rear suspension changes, production shortcuts, etc[/i] some good things, some bad, but all of which will influence a flexing frame over time. For an example of the latter, look at the plague of broken wing supports. Or guess the effect on a trad chassis if one uses a single anti-tramp bar on one side to save on cost?!! All of these things can be sorted amateur owners but that era has passed for the moment.

gmg

Do you know the estimate of maximum deflection and torsion of the chassis (cm or inch) without bending it definitively?

Again, no clue, dear CBY. (I AM enjoying this discussion with you. Right or wrong, we are definitely thinkers and researchers!. However, whatever those numbers are, they will certainly changed by the add-ons, like engines , underscuttle gussets, rollbars, gussets, etc. And how long will a flexing chassis in use remain the same without a much higher grade metal? Some countries have chassis straightening shops..done before or after the vehicle is assembled. I only recommend them (barring an accident) to moggers who have just bought a new chassis. I tell them to deliver it directly from the supplier, to the nearest chassis shop. These shops are not expensive.

BTW, I have no wish for anyone to get too ....er.... anal about what I am trying to convey. I am merely pointing out why Morgans MUST be tweaked individually and why that applies to both standard equipment and especially complex addons. Sometimes it merely takes the moving a bolt hole or shortening a bracket, or buying better components (the MMC, like most manufacturers today, picks components on cost not effect and then they fit everything identically, like the newer aftermarket tells us). So the cars can't work perfectly except by coincidence. For some Morgan generations this basic fact has been a lot of fun as moggers used to LOVE fiddling. For some generations it has been an anathema, making that generation vulnerable. I have no problem with that as I do not factor in price only effects. If a lack of simple maintenance can only be cured incidentally by spending 1500 quid on aftermarket stuff that makes the subject cars non-standard, so be it.

It should not be a shock (pun again!!!) that 100 years will produce an odd but subtly lovely suspension if one wants to get it working as it was meant be. We cannot jump to the conclusion that 100 years of old Morgan designers with infinite experience were all simpletons. Actually, like most owners, I began with THAT impression (wryly) but if I can paraphrase Mark Twain in speaking of his father, "I am amazed how much those old guys learned since I began my Morgan hobby, despite being buried decades ago!"

L.