Links
 

It's taken me a while to find the right pages; links copied here for anyone interested.

Gov.uk Vehicle Registration page with details covering kit-cars, rebuilt cars and radically modified cars.

https://www.gov.uk/vehicle-registration

Guide to getting an IVA Pass:

https://www.gov.uk/government/public...alconstruction

I think the answer to your original questions are pretty clear - a Mazda MX5 monocoque does include not only the windscreen frame but also the glass. It is bonded in, not sat in loose rubber so it becomes a structural component. The second issue is whether its just rules or is it actually a real safety issue. Personally I wouldn't want to cut into the Mazda and expect it not to be compromised. They are designed down to the tiniest gram that can be shaved off and still be safe - there's no room for error.

There are lots of unfinished Lotus seven-style kit cars on eBay and even lots that have been registered but are in need of work. You'll find designs and plans to draw from everywhere on the net.

Have you thought of a TVR? A rolling chassis pops up sometimes and will give you a modern separate chassis to build from with registration.

Ross,

I would agree with you and I plan on skimming through eBay and a few more forums to find the options out there if I can (military IT doesn;t allow eBay!). However, following up on a couple of the ideas posted here, I found this...

http://www.themx5restorer.co.uk/mx5-speedster/

That is a road-legal conversion, not subject to IVA and sold by a legitimate and well-respected MX5-oriented repair and conversion company. There are others out there too.

Cut windscreen and no wipers, one of which might, and the other definitely would, fail the S/IVA regs. I emailed the company and they affirmed that it does not require an IVA, though they had not been to Mazda for comment. If they are skating the edge of legality I'd be surprised - legitimate and experienced companies don't take significant risks like that, it could shut down the business.

I have queries in with Mazda, and will post any replies/comment here if they come back with anything useful. I'm also going to write to DVLA for a comment, see how far I get.

I'm also weighing up buying a Mk2 SE with MOT in moderate condition apart from the rusty seatbelt anchors and heavy scrapes down the RHS (which will all be stripped off anyway!).

Thank you again for all the views and comments, much appreciated!

If you cut the windscreen you will need an IVA, the windscreen surround and the bonded in windscreen are part of the monocoque.
Don't see the point of the conversion, it just looks like an MX5 with the windscreen cut in ha;f. Just means you lose the roof for no reason. Sorry but just looks stupid.

Hi Ambitious_TAS, no doubt you saw the listing in the for sale section of this forum for a TVR rolling shell? It may have sold yesterday :(
http://www.madabout-kitcars.com/foru...ead.php?t=6617

Evening JaguarTVR, sorry you may have misunderstood me. I'm after the underlying body, chassis and PPF but will have to remove the windscreen and trim the body back to fit the planned GRP shell. This gives me Mazda handling without having to design or build a spaceframe (which I don't trust myself to build to a high enough standard), and I can rely on the strength of the factory-built monocoque (even without the non-crashworthy windscreen) as well as a massively simplified build.

If I actually get on with this I will blog it!

I think the answer is to build to IVA regs anyway (which is hardly a bother), document heavily, plump for MOT and if the answer is no, it's IVA.

Thanks Ross, I'll have a look but may stick with the Mazda idea.

I wouldn't want to risk a DIY build with a chopped MX5 donor. The windscreen is a structural part of the design and to remove it or chop it down would result in the requirement for IVA testing. You wouldn't be passed just because some company you emailed said it was ok to do such a conversion. You will have to prove that such a conversion is properly designed and tested, I can't see how you would do that, do you? You could take a chance and it might be ok, that's your choice.

Lucky,

Nor would I take such a chance - hence why I am researching here, seeking collective wisdom, looking for the evidence and not simply guessing or taking anyone's word alone for it - the original question was actually about structural strength. I intend to put in further queries to DVLA and Mazda to establish a black-and-white position before I commit to anything, and in any event common sense says to build to IVA regulations rather than cuffing it. However, there is much in the way of contradictory evidence out there (such as the road-legal Speedster when compared to the DVLA regs, and the old comments by ACE posted by Paul), and I'd like to understand just what can and cannot be done safely. I don't want to start with a 1970's rustbucket or someone's half-built coathanger collection on wheels, but I do want something I can afford and build without incurring a divorce, handles like the MX5s I used to own (and loved) and will turn a few heads at the same time.

I suspect Mazda will just say they've only tested as supplied, and DVLA could say one answer and change it the next day :icon_question:

Perhaps. But I'm still going to ask, if only to understand the potential impact on structural strength and what remedial/additional work should be undertaken. I'm planning on adding structural reinforcement anyway to achieve the desired end-state.

Well cutting the windscreen isn't going to effect the strength of the monocoque chassis is it? Its just a rollover risk, which if we are being honest, is present on all convertibles anyway

I wholly agree mazdarazmataz - I'm no engineer, but the MX5 is a convertible designed from the outset without a roof structure to stiffen it, so logically the structural strength must lie in the chassis rails and bulkheads. I struggle to see how the windscreen (which is acknowledged as a non-crashworthy structure) affects the body, although I intend to brace the tub where the lower edge of the windscreen used to cross the car. The strength must surely lie in the floorpan, transmission tunnel and bulkheads.

I totally agree, it's just that the DVLA don't, You have to agree to their rules.

I think the DVLA will simply respond by saying the car will need to go through IVA if you modify the chassis. That will include the windscreen surround as its welded to the rest of the chassis and forms part of it to form the whole car.
You could challenge that by requesting all the information via a "freedom of information" request. You would then be sent bundles of paper work running to hundreds of pages, including loads of legal jargon. Good luck with that one !
I don't think Mazda will offer anything further other than to say, "don't do it" and they would just wash their hands of the idea.

Mazda themselves produced a handful of cut windscreen roadsters as a very limited run. I doubt that they went through separate type approval for these 50 or so cars. Do the hot rod guys go through iva when they do their roof/windscreen chops? ( I know those cars are sperate chassis...)

Mazda have officially acknowledged the request and are looking into it with their Technical Department at Mazda Europe. That's amazing in that's it's not a flat 'no'! I'll keep you posted.