OK, I just want to start of this debate stating that this topic is not intended to p*ss anyone off.

I was appoaching my build thinking that I should draw up my own chassis in CAD and do multiple tests to determine the strengths and weaknesses of a book chassis and how it could be improved upon. I also have noticed a number of other builders out there doing the exact same thing, and in some cases, taking it to extremes.

After some time reading others websites, papers, dissertations and studies, I came up with these questions:

Haven't the mods made by Mcsorley, Cymtrix and others who have already studied the Locost chassis dynamics had the greatest impact?

Would the limited mods I or others make at this point in time will be superfluous to the needs of any average 7 builder? So why bother?

Certainly improvements can always be made to something and I'm not trying to quash anyones creativity. It's just that I am wondering why I put in so much effort for negligible benefit on a frame design that is tried and tested?

I could understand it for those building middies or straying away from the book chassis by a great deal. But, on my first build, it's going to be fairly close to the book.

Comments?

If it ain't broke don't fix it.

As far as my build goes I have enjoyed the challenge of using the book as a guide and adapting the basic design to what I want.
Building one of these cars from scratch is always going to require an individual approach, everybody will have their own views as to the best way of achieving the aim. The contributions of others on here are invaluable but at the end of the day the car you build will be unique and as such will not conform to any set standard. We as builders decide on the level of innovation/development we incorporate into our cars and by our mistakes/sucesses may assist others in the future.

I suppose what I'm trying to say is to do your own thing but don't feel it's all been done already.

Mick

I actually enjoy looking at the different ways that everyone else has come up with to improve chassis strength. I seem to remember one car that came up with an engine cradle and increase engine bay strength by loke 1000 times. I am waiting (or rather I waited and now I've built my chassis so it's too late) to see someone come up with an ingenious design that is radically different, but keeps the same external dimension. And an extra mind thrown in could be the one that has that radical idea

Playing with autocad will cost you nothing except some time.
If you have some idea's go for it when you still can use your free time for drawing up some frame structures,once you're in the construction mode it's difficult to get back into the designer mode if you know what i mean

Couple of points.

Although Cymtriks mods seem like they make sense, they are untested as far as I know.....someone please report back when tested.

The McSorley plans aren't structural improvement mods, simply a redraw and correction of the base plans and some plus variations.....I'm a friend of Jim's and I'm sure he'll agree with me. Don't get me wrong, Jim did a LOT of work and his plans are great, but I'm sure he claims no structural changes.

There seems to be some doubt about Cymtrics proposed modofications.
I think we all agree that they dont make the chassis any weaker.
So if they are not weakening the chassis,make it lighter and probably stiffer why the hestitation to use his modifications?

My only doubts is they aren't tested....I'm fairly sure they will be OK....

My gripe is people treating his mods like gospel without some feedback.

No offence to Cymtriks I'm certain he his great at his job, but his job is not designing car chassis...again someone correct me if I'm wrong...

All I'm saying is don't carried carried away, just treat them as theorectical until tested..

Weakest link engineering never seems to get mentioned here. If you are perpetually strengthening and stiffening parts (including the chassis) at some point something has to give. If the loads are evenly spaced over the suspension joints, brackets, dampers, and chassis, there will be no appreciable problem, but if the chassis in infinately stiff, all the stress will be on the suspension and the WELDS. Its the old unstoppable force meeting the immovable object syndrome.


I am not saying that a stiff chassis is a bad thing, but taking things to extreems will cause unthought of problems

merc claim that the smart car is rigid, and 'exploits the crumple zones of the other car'.

Its strong in a sideways crash as the wheels are closely spaced and impact will be taken at those points on the side.


yeah right.


marketing bo&^cks.

how do you exploit the 'crumple zone' of a 4x4 or a volvo!


atb

steve

The A series mercs have a twin level floor so are quite good in side impacts, but I agree about the marketing blurb - merc's aint wot they used to be.

4x4's as a rule are death traps, if you have a med to heavy crash, coupled with the false sense of security they give, you are in trouble.

Volvos. They are safe, they have VERY soft extremities, and absorb shock very well, but the lethargic handling, they are more likely to need it!

Jermyn,

I think you make a quite valid point. Many (many) cars have been built to the book design or close to it. So they fall apart after the first 500 kilometers? Generally, no (need to make the distinction between design quality and build quality ).

If you're looking for a stiffer chassis, try the Australian chassis mods. We have to actually pass physical tests of the chassis here so the Aussie mods are tested and known to work.

I'm building a mid-engined car only loosely inspired by the Locost so I'm doing a fair bit of planning and checking to ensure that my chassis is stiff and strong enough to: be legal, handle well, and be safe.

If you're building a book Locost in the UK, I'd say leave it alone.

Edit: just noticed you're in the US - the only reason you might make significant chassis mods is to deal with different donor components.

Dominic

[Edited on 22/9/2004 by TheGecko]

Heard this before also but what exactly are the Australian modifications?
How are these cars tested on tortional stiffnes?
Just want to learn

quote:

---

Originally posted by Cita
There seems to be some doubt about Cymtrics proposed modofications.
I think we all agree that they dont make the chassis any weaker.

---

I started doing an analysis of my chassis using a 'simple' method that I'd read in a book.
the theory of the method was you estimated the down forces at the key joins in your chassis, and used calculation of moments to make sure you'd got everything right.

Then you drew the forces on a drawing board - in the direction of your tubes, but the length proportional to the force on the tube.

If your intersection has two unknown forces on it then you can estimate the forces on the remaining tubes by using lines parallel to the tubes and measuring the result.

My explanation ain't that good, but there's a (sort of point).

After getting halfway down the chassis and finding a bit with more than two unknowns (necessitating a guess), I started from the other end. I got 4 tubes in and discovered that I could estimate the stress on the same tube from two different intersections, and they were different by a factor of 10.
Which kind of put me off the methodology somewhat as it hadn't mentioned anything like that.

Once I flagged it away, I decided that, while it's probably not worth doing the full FEA on the chassis (for me, anyway), looking at other folks chassis ideas, and *understanding* them, then pinching what makes sense, seems like a good idea.

So I'm going to do mostly cymtriks mods, with McSorley's revised front end (not for strength, for manufacturability).

A point? Oh yeah, um.
Worth thinking about the chassis design before you cut tubes,
But only you can decide if it's worth plugging the whole thing into an FEA package or whatever.

Cheers,
Greg H

quote:

---

Originally posted by Hugh Jarce
Who says they don't? Thet're not tested! (I'm sure they won't actually make things worse though).

---

I'd go with Alan on this. Don't treat any mods as gospel. We can all come up with potential improvements - However, all these either based on experience or theory. This is why manufacturers crash test cars (any volunteers for doing the locost ones?). To put things in perspective - I know of a single seater driver who made some structural modifications to the front of a car that greatly improved the stiffness and handling over the original design - Great!
..... until he had a crash and ended up with one of his additional steel tubes impaling his leg in a frontal crash!
Sometimes there's a trade-off

quote:

---

Originally posted by Cita
Heard this before also but what exactly are the Australian modifications?

---

The Locost design was copied from the Westfield pre-lit which in turn was an interpretation of a Lotus 7/Caterham chassis. (Strange how each sued each other

Westfield, in order to get away from the anti-roll bar cum suspension arm a la Caterham, developed the wishbone with 'coffin' front end.

Now as far as I'm aware they did no CAD analysis of the design but applied engineering priciples and suck it and see.

Over the years I watched threads as newcomers come and go, each deciding that the chassis needed CAD analysis in order to improve it.

As far as I can tell, the only real mods without penalty are the minor additions that the Oz guys do. I've incorporated them in my chassis and the weight difference was something like 8kg.

However the measured benefits as done by the Oz testers bears out that these simple mods stiffen the chassis by approx 50%. The results are somewhere in Yahoo Locost list files.

As has been stated, you're wasting nothing but time when doing an analysis. If it makes you feel better , do it.

Incidently, after the Oz mods there was a distinct improvement to the cars handling along with a loss of chassis 'creaks'. Mostly from the rear panel where the rivets became 'loose' with the chassis flex.
Actually they were still tight when examined but moved under strain.

[Edited on 23/9/04 by Rob Lane]

I've just looked at the mirror site chassis jpg of Oz mods. These are not the mods I was supplied with a couple of years back by Tricky.

The mods are more like the frame mod.jpg but some items missing such as gussets at rear.

Best thing is to leave everything as per the book?
All those comments are very confusing for a not too clever guy like me.
I dont think Cymtric is sucking his knowledge out of his thumb(as our politicians do!)and his modifications are not uterly complex or expencive so why not take them and use them.
I dont want to step on anyone's toe here but i got the feeling that "i did'nt come up with this "improvement" so it probably is no good" is making a too big a fuzz about this.
All IMHO of course.

I completed an FEA for a book locost chassis around 5 or 6 years ago. My reason for this was to try and get to grips with the constraints approach in order to analyse somebody elses design for them.

In the process of doing this i made a number of mods with regards to impact safety and geometry changes. My own car incorperates these changes.

They are related to the effective strength of the floor, the triangulation and geometry of the transmission tunnel and forward floorplan (i.e. my engine just clears the footwell bulkhead), rear and side reinforcement, and front end lateral triangulation.

My advise to anybody starting out is to go with the book design or thereabouts, maybe apply the common basic mods.

If your looking to design a considerably improved car then starting with the standard book chassis is NOT the place. In fact starting with the chassis structure is not the place.

With regards to cymtriks and other detailed mods: the panelling of the transission tunnel and steel floor is not a bad idea as it gives greater strength in the passenger region, the y shapes triangulation is ala caterham so not likely to be too far wrong, but i would personally be rather hesitatant as to the triangulation between the wisbones, diagonal fore and aft. In a front ender you may loose the crushable section of the nose, this loads up the next set of tubes back, one of which ends up (on a book chassis) between your toes, putting large bending stresses in the frame.

Many 7 derivatives use this triangulation at the front but utilise lighter gauge material from the foot well forward in order to leave some sutable failure points for crash tolerance.

Only my opinion for what its worth.

quote:

---

Originally posted by MikeRJ

quote:

---

Originally posted by Hugh Jarce
Who says they don't? Thet're not tested! (I'm sure they won't actually make things worse though).

---

The modifications that triangulate the front part of the chassis, are pretty obviously going to make the structure stiffer, at least in that area.

---

My initial inclination was designing for performance. I hadn't even given any consideration to safety. But, now that so many of you have brought it up, I think you have touched on a truly important aspect of this topic. I don't want to add mods to my car that could compromise my safety in the event of a crash. And, being that I don't have a crash test course set up in my basement, I would have no way to check if my new mod wouldn't end up in my chest in a crash. OUCH.

When I started this topic, I was going to use some of the Mods already out there. Now, I'm reconsidering strenthening mods altogether. Certianly stiffening one point in the chassis has the propensity to defer force to other points, possibly causing those to fail under stresses they weren't initially designed to handle. (I still might consider the Aussie ones, since they seem to have safety in mind first and performance second. anyone got a link they can post?)

ROB- do you still have the old Oz mods you could post?

Plus, I think the issue Thegecko brought up with design quality v/s build quality is also relevant. The welds on the frame have every bit as much to do with the stiffness as any other part. So, am I to believe internet posted FEA results of some yo-yo who had no business even holding a welder?

I guess I enjoy reading their results regardless. Especially since they come up with these mythological strength increase numbers.

I think I'm still going to draw it up in cad just to make adjustments for my RX7 donor car rear end. But, as far as strength testing goes....i'll probably leave it alone

Jermyn,

The Oz mods are based upon physical findings rather than software analysis.

The chassis is put through tests by their 'rules' engineer. See the posts on the mirror site linked in above post.

I've tried to find the actual measured results but I've probably deleted them.

I will see if I can find the post from Oz with the simple mods. Certainly the first and most easiest is the two braces in front frame, turns it into a 'W'

Id go along with syd's comments.

I could stab a guess at what the "couple of tubes" which make a big difference are, based on tests and track performance on a chassis i know, but im not going to betray the trust of the owner as it is a competition vehicl which has done very well so far, it will be inetresting to see if anyone can guess what these mods may be. Theu will be on my car later in the year.

As we are talkin about analysis on this thread so my comment with regards to side panels is that YES the do have a considerable effect on chassis stiffness as does the tunnel however capturing this performance accurately allowing for fastener interaction and bondlines in beyound he scope of most, as such if they are excluded from the analysis then the analysis can be considered as a minimum stiffness guideline.

I have often wondered why people dont use a X brace rather than a single diagonal across the sides of the engine bay.... thats gotta have sone effect on stiffness.

atb

steve

I'm all for getting stuck in, learning experimenting and improving when it comes to these things - getting more deeply involved is part of the fun of any project.

That said, I don't think we should get too hung up on the chassis stiffness and performance etc. Many elements of the locost design are less than perfect but it is still a better and more satisfying driving experience than most things on the road. Your average tin-top sporting hatch is considerably stiffer but you are still going to leave most of them standing on a twisty 'B' road.

I'm not saying you shouldn't put effort in trying to improve, just don't think that your car is going to be crap if you just follow the book and a few of the basic mods - it isn't (well not for that reason anyway).

I'm just following the basic book chassis with a steel floor and tunnel, the cymtricks mods at the front and a couple of additions at the rear.

My thought being that the chassis is probably the simplest bit of the whole build (took about a week and thouroughly enjoyable) and if I get into it enough to want to improve it when the car is on the road I'll look at building another and transfering the parts over. I'm sure I won't though!

Phil

Steve,
Regarding your point of the X-Brace, my own opinion is that the problem here is that the triangulation is too long and is made of 3/4" round tube rather than 1" square. Yes an X-Brace would improve things but I think it is better to do something like I have done on my own chassis. See below: (Comments, Good or Bad welcome)

Btw, all the sheet sections you can see here are seam welded 1.6mm steel plate. (ie. Footwells, main floor and under the steering rack area)

Cheers,
Craig.



[Edited on 24/9/2004 by craig1410]

Craig,

Looks excellent, most of the mods you have are what the Oz guys developed.

Just one other thing, is that standard book steering rack mounts? If so you will need to beef those up slightly as the rack is subject to flex using the book mounts.

Update: I've just looked at your site and seen the extra strength rack mounts.

[Edited on 24/9/04 by Rob Lane]

I dont think that Cymtric made a guru of himself,all he did was post a analysis of some modifications he made,no more no less.
It's of course up to the builder to use or not use those modifications.
The only thought i have is that we all seem to except for example our crappy welding (as mine!) but when it comes to modifications all of a sudden the safety aspect is brought in.
If Mark Allanson would inspect the welding on our cars i'm sure he would scrap at least 50% as unsatisfactory,still we feel it's safe enough.

That's the way to do it! Carve the chassis in one piece from a laminated block of MDF.
Beautifully done too.
Rescued attachment MDF_chassis.jpg

Hugh,
It does look like MDF doesn't it! Never thought of that.
It's a nice gloss black now though.

Rob,
Many thanks for the compliment!
I must admit I am quite pleased at the way it evolved! It all kinda came together at the last moment to be honest as a result of my wish to build an engine "cradle" into the chassis for my Rover V8 and use the Rover SD1 original engine mounts. Also, given that it is a V8, I can't use the long "R" tube so I elected for two shorter "R" tubes. This gave me a convenient place to join my two triangulation tubes on the side so they coincided with where the "R" tubes hit the "J" tubes on the top. The changes to the front assembly are as per cymtriks suggestions but to be honest I had decided to triangulate the front anyway because it seems like such an obvious weakness.

My steel plated areas are perhaps overkill but I wanted my floor and footwells to be made from steel for safety reasons as much as structural reasons. I hope that they will stop or at least slow down any fragments of steel tubing which try to come my way in a frontal impact.

Generally speaking I have approached my build by simply trying to ensure that there are as many triangles as possible in my chassis and no large gaps between chassis tubes and/or long unsupported chassis tubes like TR1 and TR2. I also believe that a welded rollover bar is the way to go because (IMHO) it is a crucial chassis member for safety and will aid stiffness too.

By the way, a friend of mine is also using a Rover V8 engine in a +4" wider than book chassis and he originally had some problems with flexing of tubes J1 and J2 when jacking the back of his car up with the engine installed. He could actually see J1 and J2 flexing outwards and had to make some refinements to stiffen things up. I certainly can't detect any flexing of my chassis when I jack up any of the corners. I have tried sitting the chassis on four axle stands (with engine and running gear fitted) and then jacking up one corner to JUST lift it off the corresponding axle stand by maybe 1/16 inch or so. What seems to happen is that the other side lifts off the axle stand by the same amount which I think it a good sign.

Cheers,
Craig.

Interesting reading, this thread. Gonna be building another chassis next year with lots more power and these mods seem like a good idea. Does anybody have a diagram of the Oz mods?

Craid, your engine bay mods look well worth doing, as do the fully welded steel plate. Are you doing anything to the back end?

Hi Jasper,
Rather than post more pics here I will direct you to look at the APR 2004 section of my build diary on my website as there are a few pictures which show various bits of the backend. To be honest I would do the back end differently if I did it all again because I had to make some compromises due to my partially home made de-dion design. Also I would make tubes W1 and W2 out of 1" square section rather than 3/4" as I think this is a potential weakspot.

You will see I have a welded rollbar which is made from 48mm x 3mm wall black pipe. Not the strongest steel in the world but the extra cross sectional area should make up for the lack of tensile strength and it should be strong enough. I was going to fit diagonals but I needed upper harness mounts and thus had to fit a horizontal bar instead. I suppose you could triangulate it above this horizontal bar if you wanted to. My turrets above the dampers have two thicknesses of 3mm plate because your turrets need to be thicker than the rollbar material to avoid punch-through. My rear braces are partly cosmetic and partly to make up for the lack of strength in W1 and W2 as mentioned above. Fo this reason I don't consider my rollbar to be "fully sorted" and this is something I would do differently next time. I would probably relocate or do away with W1 and W2 and have proper rollbar diagonals going to the bottom corners of the rear chassis as per FIA spec.

I had to make a few changes to the seat back chassis tubes due to my unusual "inboard" trailing arms and again there is room for improvement I think but it should be reasonable.

Let me know if you have any other questions and I'll be happy to provide any help I can. I'm busy modelling my chassis in an FEA program called GRAPE to see if there are any weaknesses and will report my findings when complete.

Cheers,
Craig.

Hi Craig,

What laodcases are you using for assessing the strength of your chassis? just being nosey, sorry.

Cheers
Chris

Stressy,
Please excuse my ignorance of the technical terms surrounding Mech Eng. I'm only a mere Electronic Eng graduate...

On the assumption that "Loadcases" simply refers to the Load Constraints and Loads (Grape terminology) I am fixing the rear suspension mounts in all 6 degrees of freedom and then applying equal but opposing forces in the vertical(Z) axis for the front two suspension mounts. I've not actually completed the whole chassis in Grape yet so watch this space...

If what I have suggested is not the best way to assess chassis stiffness then I'd appreciate any advice you can give me but it seemed the most obvious way to set it up initially at least. I intend to play with different setups later to assess stuff like offset frontal impact, side impact, rollover and other relevant scenarios.

Has anyone else tried using Grape (website here) and if so, can you comment on its suitability/accuracy?

Cheers,
Craig.

My 25 öre worth.....

If it ain't broke improve it.

The book chassis works, no question about that. If something was terribly wrong this forum wold show it. We talk improvement here and a good question to ask before we star talking about what to do is: Why are we doing it?

Increased torsional stiffness is a way to improve handling. The torsional bending of the chassis will do some of the work the springs are supposed to do, only without any dampers and not as predictable. Higher torsional stiffness will give you better control over the suspension and, if you know how to exploit this, a faster and safer car.
A locost built by the book, will handle quit good, so it ain't broken. But it's not to hard to find things that can be improved to make it even a little better.

As for the original question
“Chassis Analysis: A Waste of Time?” Yes, except if you want your car to be a little faster round the track than the others.

Cheers!

Craig

Tried Grape some years back. IIRC it do beam/truss analysis. Shells would be handy to do a fair analysis of a locost chassis, since there are some stressed skins.

Your chassis look grate! I especially like the bit between the engine mounts and the bulkhead. Might “borrow” that one.

Cheers!

Leto,
Firstly, thanks for the compliments. Did I mention I had patented my design? Don't worry, the Royalties aren't that expensive...

Regarding your first posting, while I agree with all that you have said I would like to add to it that there are times where you should definitely seek to improve the standard chassis and that is when some other aspect of your design has perhaps reduced normal chassis stiffness. In my case using two shorter "R" tubes to make room for my V8 is likely to reduce chassis stiffness by a significant amount (as per cymtriks notes) so my extra triangulation is included to restore (and hopefully exceed) the status quo in this regard. Also, the Locost chassis is designed for a lighter engine than I am running and so I think it is reasonable to attempt to stiffen the chassis to cope with this.

In general, I would suggest that anyone modifying the chassis should consider the other elements of the car, in particular the suspension wishbones, trailing arms and panhard rod because the chassis changes may result in increased loads on these components. If you were to make the chassis infinitely rigid then all stresses would be concentrated into the suspension mounts and components which they were probably not designed to handle. Think of the car as a "system" of interconnected components and make sure you don't move the weak link (there is always a weak link in any system) to a component which, if it it fails, would produce a catastrophic accident.

Cheers,
Craig.

hi mate, back again, apologies for any confusion caused by my load case terminology.

Your basically correct with you response tho. when doing FEA you have constraint sets and loadsets (or cases).

Constraint sets may be for example, all four wheels supported to analyse overall bending, or 3 wheels supported one free for one wheel bumping, or rear wheels free to rotate but not move in space to look at a load applied from the front.

Loadcases correspond to these as maybe maximum braking inertia, lateral inertia, maximum bump etc.

The common approach with playing with chassis is to look at a simple torsional efficiency model, i.e twisting front to rear. This permits a comparative analysis of stiffness based on twist angle per unit load. On this basis you just need to apply a consistent approach as you are not always looking for real world values but just a comparison.

The accuracy of the constraints and load method with respect to the real world is the more complex aspect.

The thing to remember is that a comparitive stiffness test is just that, and a such strength must be evaluated seperately for the appopriate loads which may be encountered, with appropriate factors of safety applied. i think somebody already commented about the relationship between stiffness and strength?

Its also worth conemplating the stiffness to weight ultimate tradeoff and if your going really light then buckling stability.

I apologise for the vaigness of my post but it would take me days to try and cover everything!

If you ever fancy a chat just u2u and i will try and be as heolpful as i can without treading on anyones toes.

Cheers
Chris

Chris,
Thanks for that, it's quite an involved subject once you start to look into it...

Yes, I am aware that comparisons to real-world figures are not within my capability but my aim is firstly to "test" the book chassis and then see what happens when I widen the chassis 4" with everything else staying the same. Then I'll change the front end to match my own chassis and see where that leaves me. I also want to see which members are highly stressed in various scenarios to see if additional gussets or chassis tubes are necessary.

The chances are, given that I've now painted my chassis, unless I find a major deficiency this exercise is just an effort to better understand structural design and no changes will result from it.

Cheers,
Craig.

Have fun

quote:

---

Originally posted by craig1410
Leto,
Firstly, thanks for the compliments. Did I mention I had patented my design? Don't worry, the Royalties aren't that expensive...

Cheers,
Craig.

---

Just an observation that may be wrong!

It seems to me that there is some confusion or mistaking with the intentions of the chassis modifications.
Without applying any physical analysis by myself to the mods being discussed, just using what knowledge I have gained, it seems that people are mistaking modifications intended on improving chassis torsional stiffness with safety issues.

There are as far as I know of no chassis safety tests that have been conducted. All tests so far seem to be FEA torsional tests (although I may be wrong).

Making a chassis stiffer torsionally does not nessesarily make it safer, especially if material is removed to counter the extra X bracing.
It seems to me (again surmising) that the Aussie mods are the most beneficial, but without further testing it is all theoretical.
The only mods I see that could actually be called safety mods would be the addition of a full roll cage.

With an open top, open wheeled car there is very little that can be done to improve safety. Going full bodied open top can make as big a difference from a seven style car as going to fully enclosed body (tin top) from a full body car.

It is all a compromise!
So if you want it stiffer then you have nothing to loose in trying the mods, but remember that every component removed could be a safety issue.

Just my opinion!
Terry

Have alook at my post about 5 or so above this one, you will see my attempts to suggest that an indicative torsional stiffness analysis finite element approaches is mearly a stiffness comparative tool and that strength assesemnt must be dealt with elsewhere using appropriate loading and constraint conditions.

When i ran ana analysis in about 1998 i ran 6 load cases, 2 stiffness and 4 strength. static strength cases were defined based upon dynamic loading equivelence. for the front impact case a non linear approach was applied in order to better characterise the structures ultimate behaviuor and identify any potentailly failure modes.

FEA will always give you the correct answer to many decimal places, engineering is about asking it the right questions......

Craig,
constraining all six degrees of freedom on both rear mounts is technically a no no as this removes any strain in the lateral chassis tubes. This is probably a small thing, but still wrong.

I'd suggest the following:-
Rear suspension mounts constrained vertically, a rear mid point constrained laterally and axially, a front mid point constrained laterally and vertically and the front suspension loaded one side up and the other side down.

This permits the chassis to adopt its natural shape under tosional load without adding extra stiffness.

Cymtriks,
Yes I see what you are getting at and it makes sense. To be honest I've not made any progress with my FEA activities in the last couple of weeks but I'll hopefully find time in the next week or so to revisit it. I'll certainly adjust my constraints as you suggest.

Thanks,
Craig.

Stressy,

In an earlier post you mentioned making some safety mods. Are they something you can share with us?

This has been a very informative thread. "Thank you" to all who have contributed.

Regards,
Mr. (still in CAD) Pete