Wadders
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| posted on 13/9/17 at 11:23 PM |
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New TVR chassis........discuss
Interested in what people make of the new TVR chassis designed by Gordon Murray. I get the concept of i Stream from the point of view of it
simplyfying the production process, but am unsure if this will translate into a fabulous handling car.
If one of us had come up with the design on the back of a fag packet, pretty sure it would get slated on here for lack of triangulation etc. I'm
particularly drawn to the unusual front suspension pick up point arrangement, it looks crude to my eyes.
Anyhow heres a video of it.........over to you, thoughts please
https://fpdl.vimeocdn.com/vimeo-prod-skyfire-std-us/01/1567/9/232838458/825099183.mp4?token=1505355362-0x5e520b4af9a8c176400b2c249f72036570fdf29c
[Edited on 14/9/17 by Wadders]
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redscamp
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| posted on 14/9/17 at 12:17 AM |
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I find the short exhaust pipes exiting behind the front wheels interesting, it should keep our feet warm and the side windows de-iced in Scotland.
(i still wonder why Ford felt the need to run the P100 exhaust all the way to the tailgate?)
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gingerprince
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| posted on 14/9/17 at 06:17 AM |
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Looks like the link is to an expired cache. Do you have the original Vimeo link? Cheers.
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Sam_68
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| posted on 14/9/17 at 07:27 AM |
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quote:
Originally posted by Wadders...unsure if this will translate into a fabulous handling car.
All the chassis is, is a bracket. It transmist loads from one point to another, that's all.
So long as it is reasonably stiff, and not excessively heavy, it doesn't have major influence on handling, so there's no way of
judging just by looking at the iStream chassis, whether the car will handle or not. That's more about geometry, springs and damping.
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nick205
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| posted on 14/9/17 at 08:04 AM |
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quote:
Originally posted by gingerprince
Looks like the link is to an expired cache. Do you have the original Vimeo link? Cheers.
Likewise the OPs video link doesn't work for me, so can't comment.
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Wadders
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| posted on 14/9/17 at 08:19 AM |
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quote:
Originally posted by nick205
quote:
Originally posted by gingerprince
Looks like the link is to an expired cache. Do you have the original Vimeo link? Cheers.
Likewise the OPs video link doesn't work for me, so can't comment.
Yeah, sadly looks like it's been taken down, There's a lot of secrecy surrounding the new car, i'm guessing maybe TVR/GMDhave not
authorised the release.
Shame really it was a really good video, and actually showed the body shape off in a good way, which is more than any of the press release photos have
managed to do.
[Edited on 14/9/17 by Wadders]
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Wadders
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| posted on 14/9/17 at 08:23 AM |
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quote:
Originally posted by Sam_68
quote:
Originally posted by Wadders...unsure if this will translate into a fabulous handling car.
All the chassis is, is a bracket. It transmist loads from one point to another, that's all.
So long as it is reasonably stiff, and not excessively heavy, it doesn't have major influence on handling, so there's no way of
judging just by looking at the iStream chassis, whether the car will handle or not. That's more about geometry, springs and damping.
I realise that Sam, maybe i didn't word my post very well, maybe i should have said 'contribute' rather than
'translate'. All academic now anyway as the video seems to have been pulled.
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Wadders
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| posted on 14/9/17 at 08:28 AM |
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Slight update........Try this
http://istreamtechnology.co.uk/?fref=gc&dti=22...
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Sam_68
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| posted on 14/9/17 at 09:18 AM |
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I'm certain that the chassis will have sufficient stiffness to perform its necessary contribution to handling.
The bigger issue with 'proper' cars (ones with doors, complex interiors etc.) is that lack of stiffness sets up all sorts of shimmies,
squeaks and rattles that are unacceptable from an NVH standpoint. If you make the structure stiff enough to obviate these, it will be more than
stiff enough to do its job in handling terms.
The irony is that 'our' sort of cars (basic spaceframes) are laughably limp be modern production car standards, yet they still handle
acceptably.
There's an interesting parallel between the iStream chassis concept, and the Reynard Inverter, which also used a very basic, untriangulated
spaceframe that was then panelised by composite sandwich panels to stiffen it.
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Wadders
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| posted on 14/9/17 at 09:38 AM |
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quote:
Originally posted by Sam_68
I'm certain that the chassis will have sufficient stiffness to perform its necessary contribution to handling.
The bigger issue with 'proper' cars (ones with doors, complex interiors etc.) is that lack of stiffness sets up all sorts of shimmies,
squeaks and rattles that are unacceptable from an NVH standpoint. If you make the structure stiff enough to obviate these, it will be more than
stiff enough to do its job in handling terms.
The irony is that 'our' sort of cars (basic spaceframes) are laughably limp be modern production car standards, yet they still handle
acceptably.
There's an interesting parallel between the iStream chassis concept, and the Reynard Inverter, which also used a very basic, untriangulated
spaceframe that was then panelised by composite sandwich panels to stiffen it.
Interesting Sam......never seen the Raynard before.
Are you saying the bonded on composite panels add a lot of structural rigidity ? The chassis as it stands looks very flimsy when compared to say a
Ginetta G40 or an Ultima for example.
TVR are talking about a race version of the Griffith being entered into Le-Mans etc. Wonder if the chassis will be re worked on that ?
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Wadders
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| posted on 14/9/17 at 10:02 AM |
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quote:
Originally posted by redscamp
I find the short exhaust pipes exiting behind the front wheels interesting, it should keep our feet warm and the side windows de-iced in Scotland.
(i still wonder why Ford felt the need to run the P100 exhaust all the way to the tailgate?)
It's been suggested that the side exhausts are to allow a fully flat floor, a lot has been made of the aero capabilities of the design. Not
really convinced it will make a lot of difference on a road car myself.
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Sam_68
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| posted on 14/9/17 at 10:09 AM |
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quote:
Originally posted by Wadders
Are you saying the bonded on composite panels add a lot of structural rigidity ?
Yes, absolutely - particularly when they are sandwich panels, as opposed to the single-skin panels that we usually rivet to our spaceframes.
Since you mention Ginetta: they presented a concept that is almost one step further in evolution from the iStream process, at last year's Niche
Vehicle Networks symposium.
iStream uses a basic tubular steel frame as the 'former' to hang simple, almost-flat sandwich panels from, creating a very stiff hybrid
structure. One of the advantages is that the sandwich panels - being almost flat - are very easy to form. None of the usual nonsense with complex
moulds and difficult lay-up procedures.
The Ginetta proposal was somewhat similar, in that they were also suggesting simple, shallow-draft moulded sandwich panels, but in their system
they'd omit the steel 'subframe' altogether, and simply bond the panels together with structural adhesive. Apologies for the very
poor quality images - my camera flash was playing up - but this was Ginetta's result:
[Edited on 14/9/17 by Sam_68]
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Wadders
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| posted on 14/9/17 at 12:41 PM |
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Jesus Sam, that's buggered my ipad view up 
I can see how the Ginetta approach would be very stiff. It reminds me of the aluminium monocoques with steel subframes either end to hang the
suspension and engine off etc. Still not sure about the effectiveness of the panels on the TVR though.
What would be the effect on a locost chassis of replacing the floors, sidepanels, footwell panels etc with say 25mm composite, bonded into the space
frame ? Would there be a massive increase in rigidity, and if so would that be a good thing.
[Edited on 14/9/17 by Wadders]
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Sam_68
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| posted on 14/9/17 at 01:14 PM |
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quote:
Originally posted by Wadders
Jesus Sam, that's buggered my ipad view up
What would be the effect on a locost chassis of replacing the floors, sidepanels, footwell panels etc with say 25mm composite, bonded into the space
frame ? Would there be a massive increase in rigidity, and if so would that be a good thing.
Sorry - I did try to figure how to make the images automatically display at reduced size but I can't work it out!
May the fleas of a thousand camels infest the armpits of Photobucket's Chief Exec, for blocking external linking... I'm trying to use
Imgur as a replacement, but haven't got the hang of it yet. Advice from the less computer-illiterate would be welcome!
quote:
Originally posted by WaddersWhat would be the effect on a locost chassis of replacing the floors, sidepanels, footwell panels etc with
say 25mm composite, bonded into the space frame ? Would there be a massive increase in rigidity, and if so would that be a good thing.
Potentially yes, and yes (which is why Gordon Murray is pursuing that strategy with iStream). Caterham already use such an approach, in a very
half-hearted manner. The Reynolds Inverter has made a better fist of it, and I'm aware of several others who have successfully used the strategy
to make a very stiff, light 'semi monocoque'. It's not as cheap, though (honeycomb sandwich panels are quite pricey), and there are
certain issues to address to ensure that the panels are properly bonded in place, don't trap water against the steel frame, don't cause
electrolytic reaction, etc. Nothing that can't be sorted, but Locost designs tend to stick to traditional and conservative solutions.
And having owned a very limp Sylva Phoenix and a very light, stiff carbon monocoque Westfield FW00 at the same time, and driven them literally back to
back, I can tell you that the effect of the extra stiffness isn't all that pronounced, in real terms: the simple spaceframe does the job
perfectly adequately.
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FuryRebuild
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| posted on 14/9/17 at 01:23 PM |
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Looking at it, then the chassis on it's own won't be all that stiff. Stiffness utterly matters for handling - if there's flex, the
suspension can't follow the geometry it's been designed for. However, the hybrid approach he's gone for is intriguing.
If you take a read though "Race Car Chassis Construction" by Aird, there's lots in there. Essentially, the stiffest is the sandwich
or stressed skin,. However, they're time taking and expensive to manufacture. So, we look for approximates. What we do with space frames is put
in diagonals to approximate the paths of force that are achieved with sandwich panels that give the stressed skin. This is cheaper and more easy to
modify that a monocoque or chassis with sandwich panels. After all, for the panel to be effective, it has to be bonded in. Ally rivets add little in
this context.
I think Murray has achieved a good compromise of manufacturing ease and torsional rigidity (again, essential for handling).
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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Wadders
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| posted on 14/9/17 at 02:06 PM |
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quote:
Originally posted by Sam_68
Potentially yes, and yes (which is why Gordon Murray is pursuing that strategy with iStream). Caterham already use such an approach, in a very
half-hearted manner. The Reynolds Inverter has made a better fist of it, and I'm aware of several others who have successfully used the strategy
to make a very stiff, light 'semi monocoque'. It's not as cheap, though (honeycomb sandwich panels are quite pricey)
So it would seem Old Gordon knows what he's doing after all . Crafty too, as it seems the panels he's using are scrap offcuts from some
aviation process.....
Guess the proof of the pudding will equate to Top Gear test track or Nurburgring times, that seems to be how these things are quantified nowadays
Good luck to them i say, hope the thing spanks some arse and is a commercial success.
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PAUL FISHER
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| posted on 14/9/17 at 02:26 PM |
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I suppose the real test is how well it handles when it's reviewed, my guess it will be superb
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Sam_68
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| posted on 14/9/17 at 02:42 PM |
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quote:
Originally posted by FuryRebuildStiffness utterly matters for handling - if there's flex, the suspension can't follow the
geometry it's been designed for.
It matters, but (these days) only to a limited degree, realistically.
The textbook obsession with chassis rigidity dates to the days of simple ladder chassis and ash body frames. Remember that the likes of the early
Lotus spaceframes were considered a monumental leap forward, that pretty much solved the problem... yet even they were only achieving
stiffnesses of around 700-900 lb.ft/degree.
Nobody complains about the effects of lack of stiffness on Caterham's handling, yet they're only circa 2,500 lb.ft/degree, after decades
of optimising and reinforcement.
You won't find many modern production cars that are less stiff than the Mk.1 MX5 (again, not usually criticised for it poor handling), and even
that is about twice as stiff as the typical Locost.
Where the MX5 is criticised is for its refinement: it suffers dreadful scuttle shake, and shudders and squeaks like a shitting spaniel.
And that's the reason that manufacturers are obsessed with bodyshell stiffness - nothing to do with handling. A typical small hatchback
like a Ford Focus is around four times as stiff as a Mk. 1 MX5, and about 8 times as stiff as a Locost, but you can bet your ass it's not that
way because Ford wanted it to be able to lap the Nurburgring faster than a Caterham. It's because they don't want customer complaints or
perceived lack of quality because the glovebox squeaks and you can hear the door seals rubbing in their frames. 
If you're not interested in refinement, as most Locosters aren't, and you're not running the massively stiff suspension that's
necessary for a wings-and-slicks/ground effect race car, the chassis deflections relative to the suspension deflections (never mind deflections in the
tyres and bushes) are fairly trivial, so you just need to have enough stiffness (around 10 times the roll stiffness generated by your springs,
is the usual rule of thumb), then concentrate on saving weight.
In short: if the new TVR lacks stiffness to the degree that it noticeably affects the handling, it would already have failed, because nobody would pay
£90K for a car with that many squeaks and rattles!
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Camber Dave
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| posted on 14/9/17 at 05:57 PM |
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Quote from Sam 68
" You won't find many modern production cars that are less stiff than the Mk.1 MX5 (again, not usually criticised for it poor handling),
and even that is about twice as stiff as the typical Locost.
Where the MX5 is criticised is for its refinement: it suffers dreadful scuttle shake, and shudders and squeaks like a shitting spaniel. "
I bought an old MX 5 as a donor. I got it MOT’d for evaluation, added Protech dampers and uprated springs and was frustrated by the scuttle shake. It
literally shook like a wet dog – L/H front first and diagonally to the tail.
Over the first winter I made 2mm chassis rail covers and fully welded them in.
I also made a centre cross brace and front and rear crucifixes (both removable obs!).
Car absolutely transformed. No shake and as solid as a saloon. The change in direction is instantaneous and it will even take rumble strips on Track
days without shake or deflection.
Now on its 3rd year of total fun driving and the Leader is on hold till the MX 5 succumbs to rust.
There is no substitute for a rigid chassis
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