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  #1  
Old 24th January 2018, 13:10
Ambitious_TAS Ambitious_TAS is offline
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Default How far can you cut back an MX5?

Question for the wise collective.

Assume you were building a (relatively) unique re-body based on a Mk2 MX5. The re-body means you are going to lose the windscreen in order to settle the body down on top of the windscreen scuttle. Intent is to retain the existing tub.

- How far back can you cut down the top rear areas of the left and right front wings (where the windscreen pillars meet the body)?

- How much structural strength is derived from the outer sills and rear wheelarch panels, and could these be removed completely without compromising the car?

The proposed body curves sharply downwards on the outer edges hence the need to remove the outer skin. The underlying chassis structure (including high-strength and ultra-high strength panels) would be untouched; this is outer panels only.

Link here gives an illustration of the body strengths. https://www.google.co.uk/imgres?imgu...act=mrc&uact=8

Some people have gone rather further! http://5849504-656005369730150375.pr...24514_orig.jpg
Thoughts warmly appreciated.

Last edited by Ambitious_TAS; 24th January 2018 at 13:15..
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  #2  
Old 24th January 2018, 16:02
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You can remove the entire body and just bolt the 'spine' chassis with front and rear suspension subframes, engine and box into your own space-frame chassis and add a body of your own design/choosing.

That's effectively how the MEV Exocet is built (sadly most of the pics have been lost to Photobucket ransom demands, but enough remain to give you the idea) - https://www.pistonheads.com/gassing/topic.asp?t=1152576

The resulting car will need to be IVA tested, so design and build it with the IVA regs in hand and budget the extra £500 or so to get it through.

The only plus side with that is that you at least don't suffer the ignominy of a 'Q' plate, but get a registration number related to the age of the donor MX5. You'll also have a unique car to your own design.
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  #3  
Old 24th January 2018, 16:38
Ambitious_TAS Ambitious_TAS is offline
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Mr Towed,

Delighted to hear your view - I've seen many, many posts of yours and all are fascinating and enjoyable.

I've looked at a lot of the MEV-style frames and have even been up to Andy at ANC to see the Replicar frame. However, I am not convinced that I could safely build a frame (I will be a novice welder) and buying an intact one looks hideously expensive, hence I was looking into reusing the MX5 tub. It's also a ruthless bid to reduce costs - frame purchase and IVA likely to total over £4500! My proposed project is very similar to the Replicar but, since I cannot find anyone who has done the same thing I am considering, I'm keeping the actual idea to myself - suffice it to say it's a full GRP body, bow to stern (so to speak!).

A rebody seems sensible but I have come up short on whether I can do it without compromising safety (less likely) or crossing the IVA threshold. Consider the amount of chopping done on the Spitfires and Heralds that end up as A352's and the like!! Cutting the windscreen, outer skin and the windscreen support pillars doesn't strike me as compromising the monocoque since the inner structures are intact - but I openly admit I am guessing here.

Does that make sense? I must sound like a nutjob!
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  #4  
Old 24th January 2018, 17:07
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I thought you couldn’t remove the screen if the pillars were an ultegral part of the body
Different if your car had a separate chassis
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  #5  
Old 24th January 2018, 17:21
Ambitious_TAS Ambitious_TAS is offline
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Ahoy Redrat, a good point.

I've only got the IVA manual to go by - I think this falls under either:

c. Amateur Built
A vehicle is an amateur built vehicle if:
(a) the vehicle was, constructed, assembled or having previously been registered under the 1994 Act, structurally modified, for the personal use of a person (R) who is a relevant individual,

or

f. Rebuilt Vehicle
A vehicle that is a previously UK registered vehicle to which the Secretary of State is required by regulation to assign a vehicle identification number, and does not fall within the definition of an “Amateur Built” vehicle or “Vehicle manufactured using parts of a registered vehicle,” and has been rebuilt using
a replacement chassis or integral chassis/body which is of the same design and construction as that of the original vehicle and which was supplied for the purpose without having been previously used, or previously formed part of a registered vehicle.

Since I'm reusing the original body it doesn't meet the requirements of f., so it has to be limited in terms of structural modifications. Yet I've seen many cars cut back heavily that are IVA exempt - the A352 is my example.

Any idea where I'd find a reference on this, or are we in 'tester's discretion' territory?
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  #6  
Old 24th January 2018, 17:42
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I would go by the general rule with modern monocoque vehicles that it's structural unless you can unbolt it (I know that isn't strictly true). Take anything else off (such as the windscreen) then it's modified and IVA due.

The A352 gets away with this as the donor has a separate chassis.

John
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  #7  
Old 24th January 2018, 18:02
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I know the MX5 is very popular and easy and cheap to buy, but do you have to use it as a basis for your car?

Conversions of the type you refer to above, like the A352, Sammio Spyder, Fiorano Corsa and Formosa 120GR offer a number of significant advantages by using separate chassis donors.

These include: No IVA (-£500), no road tax (-£250/year), classic car insurance (-£££) and legitimate use of black plates with the option to buy a dateless plate instead of nasty reflective ones with a recent year letter.

In a low, light car the old Triumph or Scimitar chassis' actually do handle (the Scimitar was pretty good in the first place and the small-chassis Triumphs are fine once you replace all the bushes, shocks, tyres etc.), and (with a bit of engineering know-how) it's easy enough to fit a modern or uprated motor and gearbox if you want a bit more oomph under your right hoof.

Anyway, good luck with your project and these are just my thoughts...
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  #8  
Old 24th January 2018, 19:53
Lucky@LeMans Lucky@LeMans is offline
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Quote:
Originally Posted by Ambitious_TAS View Post
Question for the wise collective.

Assume you were building a (relatively) unique re-body based on a Mk2 MX5. The re-body means you are going to lose the windscreen in order to settle the body down on top of the windscreen scuttle. Intent is to retain the existing tub.

- How far back can you cut down the top rear areas of the left and right front wings (where the windscreen pillars meet the body)?

- How much structural strength is derived from the outer sills and rear wheelarch panels, and could these be removed completely without compromising the car?

The proposed body curves sharply downwards on the outer edges hence the need to remove the outer skin. The underlying chassis structure (including high-strength and ultra-high strength panels) would be untouched; this is outer panels only.

Link here gives an illustration of the body strengths. https://www.google.co.uk/imgres?imgu...act=mrc&uact=8

Some people have gone rather further! http://5849504-656005369730150375.pr...24514_orig.jpg
Thoughts warmly appreciated.
Have you thought about basing your project on existing kit car chassis, one of the less popular space frame or ladder frame types? Plenty of Locost's, Dutton's, Jago's etc out there for very little money. Find one that is correctly registered and you are ready to put any body on you like .
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  #9  
Old 24th January 2018, 21:48
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Quote:
Originally Posted by Lucky@LeMans View Post
Have you thought about basing your project on existing kit car chassis, one of the less popular space frame or ladder frame types? Plenty of Locost's, Dutton's, Jago's etc out there for very little money. Find one that is correctly registered and you are ready to put any body on you like .
An interesting twist......... Could the new car then be a "Dutton Formosa" or similar? Most of us would regard such a beast as incorrectly registered
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  #10  
Old 24th January 2018, 21:59
Lucky@LeMans Lucky@LeMans is offline
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Quote:
Originally Posted by Mitchelkitman View Post
An interesting twist......... Could the new car then be a "Dutton Formosa" or similar? Most of us would regard such a beast as incorrectly registered
Why would that be ? As long as the kit chassis isn't modified it would just be a body swop in the eyes of the DVLA. It would be exempt from IVA the same as most other body swops on any mass produced cars.
You just need to fill in the paper work as normal.
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  #11  
Old 24th January 2018, 22:11
Mitchelkitman Mitchelkitman is online now
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Quote:
Originally Posted by Lucky@LeMans View Post
Why would that be ? As long as the kit chassis isn't modified it would just be a body swop in the eyes of the DVLA. It would be exempt from IVA the same as most other body swops on any mass produced cars.
You just need to fill in the paper work as normal.
Purely because of the new name! How many times have we seen a Robin Hood masquerading as a Dutton, but of course it looks nothing (or not a lot) like a Dutton. Given several years from now, who would know it has a genuine Dutton chassis or not?
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Old 24th January 2018, 22:31
Lucky@LeMans Lucky@LeMans is offline
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As long as the rules are applied properly there would be no reason for such a re bodied car to be incorrectly registered. What your saying above is another matter altogether unless you wanted to put Robin Hood panels over a Dutton chassis which wouldn't be a issue, but it would be a bit pointless ??!!
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  #13  
Old 24th January 2018, 22:38
Lucky@LeMans Lucky@LeMans is offline
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Quote:
Originally Posted by Mitchelkitman View Post
An interesting twist......... Could the new car then be a "Dutton Formosa" or similar? Most of us would regard such a beast as incorrectly registered
Yes, that what be a reasonable assumption , "Dutton Formosa". As long as that name is reflected on the V5 everyone is happy.

My own plans include a Westfield Giordanengo Testarossa project.
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  #14  
Old 25th January 2018, 06:03
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I'm with Lucky on this one - I can't see any legal issues in rebodying an already registered kit car, so I say go for it!

It'll give DVLA a bit of a headache and occupy their time for quite a while trying to work out whether to rubber-stamp the paperwork, and while they're doing that I'll slip my Triumazdaporscheford 356 Outlaw through the system unnoticed...
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  #15  
Old 25th January 2018, 08:02
Ambitious_TAS Ambitious_TAS is offline
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Default What constitutes 'structural modification' for IVA purposes?

Wow, that's a lot of replies! Fantastic!

I'm put off using an older donor for a number of reasons, not least that the older cars are more likely to have complex corrosion issues in the tub and be needing a ground-up restoration of the running gear. I've previously owned both MX5's and an MGB (the latter consuming much of my time and spare cash just to keep running!), and the quality and handling of the Mazda is what I want - it's a brilliant car and a great basis for the build as many have shown. The MX will probably need some corrosion treatment in the sills but it's well documented and the build quality is high; I am working on the basis that the running gear (the powerplant frame) will not need much work at all, hence I can get the car built fairly quickly. I can work with the modern plates; it's not the end of the world.

The Locost approach is worth a look, I'll see what is available. However, I would have reservations about using a kit - who knows how well or how badly it's been assembled, and I'd be pushing my limits on recognising a good job over a bad one. I've done a brief online search (never authoritative) and finished kit cars seem to attract a relatively high price as well, more so than a shabby MX5 and perhaps closer to a bespoke spaceframe. Can anyone point me towards an example of something that would, for example, be suitable to sit under a Replicar-type body? It would definitely need the Mazda's wheelbase (2265mm), track width (1415mm) and seating position.

This thread has really helped me to understand what I think is my fundamental question - what constitutes 'structural modification' in regards of an IVA? If anyone can point me to a definitive link (it's not defined in the IVA manual), I would be most grateful. I suppose that in the long run, if I did go with the MX5 rebody, then an IVA is probably manageable.

Just a quick note - those of you building the cars out there, you are all a real inspiration and your build logs make for great reading - thank you!
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  #16  
Old 25th January 2018, 08:02
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Ambitious_TAS – The rules are a bit confusing when it comes to a ‘rebody’.

I think your question covers two separate, but related, issues:
- Keeping the original registration number.
- Maintaining the structural integrity of the MX5 bodyshell.

So first things first…

If you want to keep the donor car’s registration number you can’t cut the MX5 windscreen off.
( And yes other people may have, but that doesn’t mean that their car is legal. )

The DVLA rules are here:

https://www.gov.uk/vehicle-registrat...tered-vehicles

The requirement is for an “unmodified” monocoque bodyshell.

The MX5 monocoque includes the windscreen.



As others have said, the A352 example is different because the DVLA identity lies with the chassis.

In my case, my registration number was linked to this.



Which allowed me to cut the windscreen off a secondhand body tub to use as a bulkhead.



So if you have to cut the MX5 windscreen off then you lose the original registration number and need to pass IVA.

Unfortunately, I can’t help much with the structural questions if you do go down this route.

Hope that helps, Paul.
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Old 25th January 2018, 08:15
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Sorry our last posts crossed.

Quote:
Originally Posted by Ambitious_TAS View Post
....what constitutes 'structural modification' in regards of an IVA? ...
This is a quote from ACE, who were the experts in this, but have now closed.

"Monocoques

It is NOT acceptable for the bulkhead, or transmission tunnel area, to be modified.

The specification for a monocoque will vary with each manufacturer and the decision on what are acceptable modifications will be based on those criteria for each vehicle.

It is acceptable for additional seam welding to be carried out."


I read that as being you might be able to argue that the windscreen frame was not part of the monocoque.

But you may need something official from Mazda to support that.

I would certainly do a bit more digging before starting up the angle grinder.

Also it might be worth contacting Kapri over on the "Rods 'n' Sods" forum for advice.

Due to people messing him about, he now asks for a charity contribution for his help.

But without a doubt, he is the UK expert in DVLA rules.
( His advice lead the way for the Sammio, Miglia and Tribute rebodies. )

Cheers, Paul.
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Old 25th January 2018, 08:18
Ambitious_TAS Ambitious_TAS is offline
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Paul,

That link is very clear, thank you, and it's what I was missing. I'm really not in the least bit fussed about the registration number, it's the car I'm after. Fun for me to drive, unique and will turn a head or two. I care not if the perfectionists get sniffy on closer inspection!!

Thank you - a real help.
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Old 25th January 2018, 08:27
Ambitious_TAS Ambitious_TAS is offline
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Paul,

Posts crossed indeed! That's a good shout - I will give both pathways a try.

I've just transposed the windscreen frame from the MX to the proposed new body using my graphics package - I nearly threw up, so I'm not keeping the windscreen!!

Thank you again - very much appreciated.
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  #20  
Old 25th January 2018, 08:54
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Quote:
Originally Posted by Mister Towed View Post
I'm with Lucky on this one - I can't see any legal issues in rebodying an already registered kit car, so I say go for it!

It'll give DVLA a bit of a headache and occupy their time for quite a while trying to work out whether to rubber-stamp the paperwork, and while they're doing that I'll slip my Triumazdaporscheford 356 Outlaw through the system unnoticed...
I agree with what yourself and others have said - there shouldn't be an issue. I could see DVLA (or someone in DVLA) getting all funny about it though? Maybe saying it wasn't an original chassis or some such nonsense, so IVA required?
I clearly don't trust DVLA to either a) be consistent in their application of 'the rules' or b) Understand their 'rules'.
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