How about a stainless steel chassis with extra features?

[GrUmPyBoDgEr]

I can't imagine any company taking on the Design & Development of any of the ideas mentioned here.
We have good replacement Subframes for our Elans made from mild steel which correctly prepared & looked after well will keep for a long time.
There was a recent thread where many owners were telling us of their cars still on original frames.
The Spyder frames, which I as a mechanical Engineer favour, were drawn up (dare I say Designed) & tooled in the 70's so the costs back then would not be comparable to those today.
Also back then there were a lot more Elans needing new frames so the outlay was offset by demand.
I think that today even the well known suppliers of Frames struggle with the lack of customers.

Cheers
John

[bill308]

The original Elan was supposed to be a fiberglass monocoque, a replacement for the Lotus 7, according to Ron Hickman as discussed in Club Lotus News - Issue 2 - April 2010 found here:

http://www.type26register.com/lotus_news_archive.html

Because of difficulties associated with attaining sufficient strength and stiffness in a roadster design and schedule constraints, a steel subframe was adopted. Individually, neither the body nor chassis would do the job, but together, a satisfactory solution was born and applied to several follow on Lotuses and even the short lived DeLoren. An example of how the chassis and body work together to achieve the structural goals is how the rear suspension towers are tied together by a verticle fiberglass wall and compound body contours to form a rigid structure.

Tim,

No doubt a satisfactory aluminum subframe could be made but I'm not sure what would be gained. Given that the steel subframe is less than 100 lbs, I'm not sure any weight reduction would be worth it considering the strength and fatigue resistance of aluminum is less than that of steel. It is possible to beef up the thicknesses where necessary, but to know exactly where and how much and still save weight, would likely require a complete finite element structural analysis of the combined chassis and body structure. This would be a lot of work. Of course one could make an initial guess and cut or add material based upon road testing, also a time consuming endevor.

MintSprint,

A stainless steel chassis would be a lot easier. Right off the bat, one could simply replace all mild steel pieces with identicle stainless pieces and probably not give up anything except for a propensity for corrosion. One would have to choose the right alloy and use the correct welding rods, but on the surface I don't think one would have to plow any new ground. The material costs would be perhaps 3 times as much as mild steel, but we're talking less than 100 lbs of material and the correct stainless can be welded quite nicely. Hydrogen embrittlement (corrosion) can be a concern after bending stainless but again, this could be avoided with the correct choice of alloy.

persiflage,

One of these days I'll have to get out to Reno to see and hear those warbird engines at full tilt.

bengalcharlie,

I'd sure like to have a chat with the owner of the stainless chassied +2.

In reality, I wound up purchasing an unpainted TTR race frame. Before I even got it home I had it sand blasted and powder coated by a local shop. Interestingly, the frame was shipped in a container and had developed some light surface rust in shipment. Where I live in Connecticut, USA, the roads are treated with salt during the winter months, so corrosion is a significant concern for me as I plan to drive the car year round.

Bill

[MintSprint]

MintSprint,

A stainless steel chassis would be a lot easier. Right off the bat, one could simply replace all mild steel pieces with identicle stainless pieces and probably not give up anything except for a propensity for corrosion...

It depends on the grade, of course, but as a general rule stainless is quite a bit more brittle than mild steel, hence a lot more prone to fatigue cracking.

There was a kit 'replica' of the Lotus Seven here in the UK a few years ago that used a stainless steel monocoque; it proved dangerously prone to cracking, despite having allegedly been fabrictaed from a suitable grade of austenitic stainless steel.

Given that the standard mild steel Elan backbone is prone to cracking around the front fork and diff mountings, in any case, I'm not sure how good an idea it would be to simply make a direct copy with identical stainless pieces... it might not corrode, but if it's lifespan is a quarter of that of a galvanised MS chassis because it cracks in use, the benefit would become rather academic.

Given that a standard galvanised MS chassis or a much stiffer Spyder spaceframe can be expected to last 20+ years, it seems a lot of effort, and risk, to solve a problem that doesn't really exist?

[msd1107]

John,

I can't imagine any company taking on the Design & Development of of the MK I, II, III, IV etc. It took an enthusiastic person willing to invest innumerable uncompensated hours to develop a product. If the product meets the needs of others, then maybe that can make some kind of business of it.

Come to think of it, this describes a high percentage of the after market auto industry, both in the UK and world wide.

Back in the '60s, a friend needed a school project. We came up with this wild idea to design a replacement 6-speed gearbox for our 4-speed unit (in a CB-72). The design got done, but then his professor decided cutting gears was too easy a project! Too bad. Maybe I would be manufacturing drive train components instead of programming. We did this even though both of us had jobs, school, and girl friends.

Even though the Lotus is a low volume car, there is more than one source for replacement cylinder heads, replacement cylinder block, chassis, suspension, and various other components. Nobody makes a full time living at this, but enthusiasm and sweat equity keep things bubbling along.

A replacement SS chassis is probably within the grasp of several of us. A monocoque carbon fibre replacement body is more of a technical challenge. It depends on getting a few crazy people together with the appropriate skills. A replacement gearbox is not that difficult, since the hard part is done by the machine shop who are literally just replicating existing gears and shafts with a different number of teeth.

Just my slant.

David
1968 36/7988

[GrUmPyBoDgEr]

John,

I can't imagine any company taking on the Design & Development of of the MK I, II, III, IV etc. It took an enthusiastic person willing to invest innumerable uncompensated hours to develop a product. If the product meets the needs of others, then maybe that can make some kind of business of it.

Come to think of it, this describes a high percentage of the after market auto industry, both in the UK and world wide.

Back in the '60s, a friend needed a school project. We came up with this wild idea to design a replacement 6-speed gearbox for our 4-speed unit (in a CB-72). The design got done, but then his professor decided cutting gears was too easy a project! Too bad. Maybe I would be manufacturing drive train components instead of programming. We did this even though both of us had jobs, school, and girl friends.

Even though the Lotus is a low volume car, there is more than one source for replacement cylinder heads, replacement cylinder block, chassis, suspension, and various other components. Nobody makes a full time living at this, but enthusiasm and sweat equity keep things bubbling along.

A replacement SS chassis is probably within the grasp of several of us. A monocoque carbon fibre replacement body is more of a technical challenge. It depends on getting a few crazy people together with the appropriate skills. A replacement gearbox is not that difficult, since the hard part is done by the machine shop who are literally just replicating existing gears and shafts with a different number of teeth.

Just my slant.

David
1968 36/7988

David,

a point well made.
We have Universities here always searching for research work & they were frequent visitors in my last job. Of course the funding was paid willingly by BMW because the job would get done more cheaply than doing it "in House"
The demand for Elan frames will be considerably less than that for Engine parts though, considering the variety of Competition Cars still using the Twin Cam & Competition = Big Bucks.
Another argument is the quest for originality amongst the majority of Elan Owners; a Spyder frame (which IMHO is infinitely better than the original) is a big no no so other alternatives would stand little chance of being widely accepted.

Cheers
John

[cliveyboy]

No one has mentioned stainless steel weighs more than mild steel.
Clive

[bill308]

cliveyboy,

I took a quick look at my materials selector from 1993. I don't think they publish this any more, but here is what I found as far as material density.

All numbers are in lbm/cu in.

Stainless steels; specialty grades; wrought 0.276-0.291
Stainless steels; standard austenitic; wrought 0.27-0.29
Stainless steels; standard ferritic grades; wrought 0.27-0.28
Ultra-high strength steels; wrought 0.276-0.29
Carbon steels, carburizing grades; wrought 0.283
carbon steels, hardening grades; wrought 0.282-0.283

From my Mechanics of Materials text book (I actually took the course from one of the coauthors, E Russell Johnston, Jr., of Beer and Johnston fame, a really talented professor).

ASTM-A36, A242, A514 0.284
Stainless (302) cold rolled or Annealed 0.286

So if we accept the Mechanics of Materials values:

0.286/0.285=1.0035 or stainless steels are about 0.35% heavier. So, you are correct, depending on the alloys selected, stainless is heavier.

I think a standard elan frame weighs about 75 lb. A TTR frame probably weighs a little more, lets assume 85 lbs.

In mild steel 85 lb
In Stainless steel 1.0035*85=85.3 lb

But, you don't have to paint a stainless chassis. All else being equal, a stainless chassis can be lighter. I think the bottom line is I'd rather pay the additional costs for a superior material and have the peace of mind of not worrying about corrosion, especially in the vaccum tank and front turrette area. Remember I live in north eastern USA and I would like to drive the car year round. Live by the sea and corrosion may also be an issue. Live in the mid east or Nevada and corrosion may not be an issue.

To get TTR or Pat Pat Thomas to agree to fabricate a SS chassis to say 26R specs is another issue. In the end, I elected to go for a TTR 26R frame and powder coat it. Afte all, I had an opportunity to participate in a container shipment courtesy of Lee Chapman of Lee Chapman Racing in the USA. This was a snap decision. I went with a gloss black from the guys who powder coat the ERA cobra replicar chassies. It looks great, but I think I'd rather have a naked Stainless chassis.

Bill

[cliveyboy]

Admittedly the weight difference is very small.
When I order steel the figures I use are:-
Mild steel 7700kg/m3
Stainless steel 8000kg/m3
Its very rare that the extra 300kg is an issue.
Clive