Lotus Elan

Torsional rigidity of the Elan Chassis

PostPost by: Frogelan » Fri Apr 17, 2020 1:04 pm

I'm writing an article at present on Lotus and I'm missing one little statistic: a reliable figure in lb/ft/degrees for the Elan chassis (with or without the engine).

There have been some impressive threads with some interesting claims, but does anyone have a solid source by any chance ?

Many thanks


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PostPost by: alan.barker » Fri Apr 17, 2020 2:22 pm

I suggest you look at past posts
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PostPost by: trw99 » Fri Apr 17, 2020 2:49 pm

Andrew,

From the Motor magazine article 'The Lotus Elan 1500' published 10 October 1962:

"The complete frame weighs 75 lb. and its stiffness is given as greater than 4,500 lb.ft/degree twist between the wheel planes. The true figure may well be nearer 6,000, which is about twice that of the Lotus Elite and very much more than one could hope to attain with a practical multi-tube frame of reasonable weight."

The same figure is given in the first road test of the 1600 by US magazine Road & Track of December 1962. However, Autocar magazine says "Torsional stiffness over the wheelbase is 4,000 lb-ft per degree, which goes up to 4,500 lb-ft with the body attached. It was as a result of tests on this chassis that Chapman decoded to make the monocoque Lotus 25 Formula 1 car; for once, instead of racing improving the breed, the breed improved racing."

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PostPost by: Matt Elan » Fri Apr 17, 2020 3:05 pm

I concur with Tim re the 4000 lbs per degree of 'twist'. However to put that into context, when developing the Triumph Stag body Triumph engineers were worried that its torsional stiffness was around 4500 lb per degree mark, giving rise to much scuttle shake and unwanted body movement. The insertion of the beam joining the top of the roll bar to the windscreen, creating the car's distinctive 'T' bar, raised the body stiffness to a much more acceptable value of over 6000 lb per degree.
So the Elan chassis is not that good torsionally but with the addition of the firmly bolted on body shell everything is fine.
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PostPost by: Frogelan » Fri Apr 17, 2020 3:09 pm

Thank you Tim.

I know that this subject is a Loch Ness monster (which is why I made the post Alan - I did check before posting) and it is useful to have an update.

I'm writing an article on the Lotus 25 for Via Retro (a Danish blog published in English) and the figures I have from John Tipler's book (Lotus 25 & 33) are:

Lotus 24: 700 lb/ft
Lotus 25: 1,000 lbft (without FWM V8 engine) and 2400 lb/ft (with the engine as it had 8 mounting points).
These figures come from Motor 15/01/1966.
Lotus 33: 2 400 lb/ft (very similar to the 25 anyway)
Lotus 79: 3 000 lb/ft (was not considered very good at the time and according to Andretti, dropped off during the season).

The figure given by Motor for the Elan seems very high compared to these figures as the Tipler book cites 400 lb/ft for the prototype Elan...

All ideas would be useful. Were F1 cars really not so particularly good "back in the day" ?
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PostPost by: trw99 » Fri Apr 17, 2020 3:33 pm

It would seem pretty clear that the 4,500 figure quoted by three magazines at the time of the Elan launch were provided by the factory marketing department.

I feel comparing the figures with those for the Stag is not quite in context, given the construction methods and material used were different and some what, five or six years after the Elan chassis was designed? I suspect, though have nothing to go on, that the other Lotus racing cars figures were for the chassis alone; and the engine in the 79 was part of the stressed structure too.

However, I am no engineer, stressed or otherwise, so hold my hand up to being at the limit of my knowledge on this matter!

Tim

PS As a complete aside, have you noticed how very many current Elan owners have some sort of engineering background?!
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PostPost by: Matt Elan » Fri Apr 17, 2020 3:44 pm

Initial design of the Stag started in 1964, so it was only a few years older than the Elan - it took a long time to get into production mind. I used it as an example of roughly contemporary cars and the relative stiffness of the two models to give a feel for the industry norm for all cars at the time.

In that context the figures given for the Lotus racers seem very low, especially as Lotus were renowned for their chassis design, producing light and stiff structures to which they could fit their long travel compliant suspension which gave them such an advantage. Are the figures quoted really ft lb per degree of flex? If so I'm surprised.
Last edited by Matt Elan on Fri Apr 17, 2020 4:41 pm, edited 1 time in total.
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PostPost by: srineer » Fri Apr 17, 2020 4:39 pm

"As a complete aside, have you noticed how very many current Elan owners have some sort of engineering background?!"

I am also a Europa owner and observed the same...mechanical, electrical, and aeronautical engineers, and other professions not strictly engineering but in some very technical occupations...eg, airline pilots. I conclude that, for whatever reason, Lotus owners generally are FAR more knowledgeable than most. I have heard it said that Porsche owners, too, are also have similar backgrounds, but having absolutely no corroboration my guess is that Lotus owners have these sorts of backgrounds more than any other owner group.

I admit to being intimidated at my lack of knowledge when i socialize with other Lotus owners.

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PostPost by: benymazz » Fri Apr 17, 2020 4:45 pm

trw99 wrote:PS As a complete aside, have you noticed how very many current Elan owners have some sort of engineering background?!


Majoring in mechanical engineering right now! My focus is in high performance vehicles :D

My dad (original owner of my Elan, PhD in metallurgy and materials science) made a similar observation - that he never saw more Lotus than when he was at MIT in the late 1960s.

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PostPost by: Citromike » Fri Apr 17, 2020 4:57 pm

My observation as a 40-year Lotus owner in the US and UK is that Lotus owners tend to be loners, consultants and engineers. That is, Nerds. Thus the Lotus social scene is a bit dull, compared to other brands. As demonstrated in this thread, conversations are technical not theatrical.

Just look around at any multi-marque car show ...

I’m not complaining nor criticizing; please don’t shoot me.

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Tech writer, SAE member, nerd.

PS - in this vein I was reading an article about Formula 5000 which said by the end of the race many of the cars were “on their knees” having sagged, bent or broken. Stiff at the beginning but not at the end...
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PostPost by: vincereynard » Fri Apr 17, 2020 5:45 pm

I suggest a figure of 4500 lbs / degree was more Chapman fantasy than fact. I read (a while ago) that when the Elite/Excel was developed work was done to stiffen the essentially very similar chaissis for NVH purposes. The Excel being a major move upmarket.

According to the Mark Hughes book, when the Elan (M100) was developed it eventually gave a figure of 5800 lbs. 3 TIMES the figure for the then current Lotus chassis. Which was the Excel!

Which leaves an original Elan chassis as somewhere between spagetti and a British rail sandwich.
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PostPost by: Matt Elan » Fri Apr 17, 2020 6:02 pm

....and I am surprised - according to quotes in Karl Ludvigsen's 'Colin Chapman - Inside the innovator' the .
frame of the Type 24 was only 700 ft / lb / degree and they were constantly flexing and having to be welded up. Apparently the Lotus 33 was 2,400 ft /lb / degree and the 38 was around 3,000.
so the Elan chassis was in fact pretty good from a racing perspective - assuming it was actually 4500..... :D !

A little bit of digging shows various modern road cars to be around 7,000 lb / ft / degree (or around 10,000 Nm per degree) - not that much more than the Stag (or Triumph 2000).
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PostPost by: Davidb » Fri Apr 17, 2020 6:28 pm

I would very much doubt the bare Elan chassis was anything like 4500 lb/deg!
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PostPost by: 661 » Fri Apr 17, 2020 7:03 pm

Citromike wrote:My observation as a 40-year Lotus owner in the US and UK is that Lotus owners tend to be loners, consultants and engineers. That is, Nerds. Thus the Lotus social scene is a bit dull, compared to other brands. As demonstrated in this thread, conversations are technical not theatrical.

...


I resemble that remark
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PostPost by: Gordon Sauer » Fri Apr 17, 2020 7:34 pm

So I just replaced the hinge in one of my Esprit doors and was not going to do the other one but wanted to be sure they both had about the same opening resistance. I took a fish scale and attached it to a built up piece from the two locating screws and found it to take about 23 pounds. So I’ve got my Elan S3 DHC body and chassis separated with the motor in the chassis, but I’ve got my PhD in psychology so is there any way to measure my torsional rigidity by hanging a rear wheel from the tree and hiking it up or something, we ought to figure out how to do it in 2020. Gordon Sauer
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