Caterham 160 the dinky one - who's built/run/bought one
Discussion
Equus said:
It was designed (by Stuart) to be put through the MSVA, though, which ought to be equally critical of such fundamentally bad engineering.
The Exocet's chassis is an abortion: it has negligible torsional bracing in the engine bay, and the Mazda PPF is designed as a simple brace to link the engine/gearbox in a fixed relationship to each other, not to contribute substantially to the structure as a whole (which is how MEV tries to use them).
Robin Hood sold many, many more than a thousand of their cars. All that tells you is that there are lots of people with as little money as they have engineering sensitivity, and who will therefore happily buy something because it is cheap, in blissful ignorance of the fact that it is also rubbish.
How much torsional bracing does it have? how much does it need? does it have more or less than other 'similar' cars? what would you do if you were building one yourself?The Exocet's chassis is an abortion: it has negligible torsional bracing in the engine bay, and the Mazda PPF is designed as a simple brace to link the engine/gearbox in a fixed relationship to each other, not to contribute substantially to the structure as a whole (which is how MEV tries to use them).
Robin Hood sold many, many more than a thousand of their cars. All that tells you is that there are lots of people with as little money as they have engineering sensitivity, and who will therefore happily buy something because it is cheap, in blissful ignorance of the fact that it is also rubbish.
in relation to the PPF, did Mazda design it as a simple brace? what issues do you think will be caused by not using it that way?
Oooh, a quiz. I like quizzes! 
Curved main tubes further reduce the effectiveness; they mean that the loads are partially transmitted in bending rather than in pure tension/compression, as is the case for a properly designed and fully triangulated spaceframe.
Neither is there any continuous 'backbone' transmission tunnel down the cockpit of the Exocet: there is a partial, sheet steel tunnel toward the rear, but it doesn't actually link to anything.
The Exocet chassis is basically two longitudinal lattice spars with very little of substance linking them.
But the bigger risk is disproportionate and unpredictable structural collapse of the chassis in an accident.
On other FE/RWD spaceframes (such as the Caterham 7) It is normal to provide diagonal bracing on both the upper and lower horizontal planes of a spaceframe in the engine bay, and a continuous, triangulated tubular backbone through the cockpit that links the scuttle bulkhead to the rear bulkhead. The cockpit bay of such cars is usually the weakest part, torsionally, so this approach is normally considered essential these days, to impart adequate overall stiffness.
See comparative example above: the black chassis is a 'Locost', which is itself regarded as a pretty mediocre example of a 'proper' spaceframe.
It's effectively a simple, C-section aluminium channel. It has naff all torsional stiffness:
The PPF has been known to crack, even in its original application where all it is being expected to do is to hold the gearbox and diff in fixed relationship to each other.
Other spaceframes that use the Mazda running gear tend to ditch the PPF, as it is pretty much worthless dead weight, and instead mount the components directly to a properly stiff spaceframe structure.
ikarl said:
How much torsional bracing does it have?
On the engine bay: none, zero , zip , nada: the engine bay is completely open, top and bottom: Curved main tubes further reduce the effectiveness; they mean that the loads are partially transmitted in bending rather than in pure tension/compression, as is the case for a properly designed and fully triangulated spaceframe.
Neither is there any continuous 'backbone' transmission tunnel down the cockpit of the Exocet: there is a partial, sheet steel tunnel toward the rear, but it doesn't actually link to anything.
The Exocet chassis is basically two longitudinal lattice spars with very little of substance linking them.
ikarl said:
how much does it need?
The usual target is a torsional stiffness that is at least ten times the roll stiffness offered by the suspension.But the bigger risk is disproportionate and unpredictable structural collapse of the chassis in an accident.
ikarl said:
does it have more or less than other 'similar' cars?
Less. On other FE/RWD spaceframes (such as the Caterham 7) It is normal to provide diagonal bracing on both the upper and lower horizontal planes of a spaceframe in the engine bay, and a continuous, triangulated tubular backbone through the cockpit that links the scuttle bulkhead to the rear bulkhead. The cockpit bay of such cars is usually the weakest part, torsionally, so this approach is normally considered essential these days, to impart adequate overall stiffness.
See comparative example above: the black chassis is a 'Locost', which is itself regarded as a pretty mediocre example of a 'proper' spaceframe.
ikarl said:
what would you do if you were building one yourself?
Build a properly triangulated, conventional, straight-tube spaceframe, not a curved tube exoskeleton bad budget copy of the already structurally flawed Ariel design.ikarl said:
in relation to the PPF, did Mazda design it as a simple brace?
Yes.It's effectively a simple, C-section aluminium channel. It has naff all torsional stiffness:
The PPF has been known to crack, even in its original application where all it is being expected to do is to hold the gearbox and diff in fixed relationship to each other.
ikarl said:
what issues do you think will be caused by not using it that way?
It contributes a negligble amount to the beam and torsional stiffness of the chassis, when it is apparently being expected to contribute a great deal.Other spaceframes that use the Mazda running gear tend to ditch the PPF, as it is pretty much worthless dead weight, and instead mount the components directly to a properly stiff spaceframe structure.
Edited by Equus on Tuesday 3rd May 16:36
Equus said:
ikarl said:
how much does it need?
The usual target is a torsional stiffness that is at least ten times the roll stiffness offered by the suspension.But the bigger risk is disproportionate and unpredictable structural collapse of the chassis in an accident.
ikarl said:
does it have more or less than other 'similar' cars?
Less. Mr2Mike said:
So what is the actual measured torsional stiffness value? If you are making comparisons you presumably have that number to hand.
No, and I know for a fact, Mike, that you know enough to know that you're being deliberately provocative by asking that question. 
You know perfectly well that spaceframe manufacturers are very reluctant to release torsional stiffness figures for their chassis, because even the best of them look dreadful in comparison with even the most mundane unitary construction 'shopping car'.
All you can do, short of actually testing them yourself, is to form judgements based on obvious structural features.
But as I said, torsional stiffness is actually of secondary importance to crashworthyness, and any curved-tube lattice frame without comprehensive transverse bracing is an accident waiting to happen: the curvature means that the load paths fall outside of the cross-section of the tubes, therefore it is subject to bending loads which thin-walled tubes do not like one little bit. It can fold up with very little resistance, if you happen to get an impact from the wrong angle.
Given the family history I'd be more inclined to go sideways (!), find a neglected Austin Seven Swallow and restore it - you'd have something amazing at the end and a genuinely important car that'll be great to drive and show.
There's just something a bit pony about the Seven 160 that I can't put my finger on - penny-pinching pastiche, almost. The elephant in the room for me is the Westfield XI, which is way more desirable and IMO better value for money.
There's just something a bit pony about the Seven 160 that I can't put my finger on - penny-pinching pastiche, almost. The elephant in the room for me is the Westfield XI, which is way more desirable and IMO better value for money.
LongLiveTazio said:
The elephant in the room for me is the Westfield XI, which is way more desirable and IMO better value for money.
Absolutely. The Westfield Eleven is a lovely little thing, and just about the only kit car I can think of where the second-hand value of a well-built one is considerably more than the cost to build it (they can go for north of £20K, and cost £10K for the kit, plus an MG Midget donor, plus cost of IVA, paint and sundries.The only thing that frightens me off buying one myself is that they necessitate an extremely dodgy approach to IVA, and it would be just my luck that I'd buy one, spend 2 years building it, then find that there's a clampdown on blatant abuses of the IVA test and I'm unable to register it.
Equus said:
No, and I know for a fact, Mike, that you know enough to know that you're being deliberately provocative by asking that question.
Not at all, several kits (including locost chassis) have been measured. An experienced eye can say if a chassis is likely to be good or bad, but until it's actually measured then anything else is conjecture. Stating that it's definitely less than other similar cars when you really don't know is poor form don't you think? "In my opinion it's likely to be worse" is certainly not the same as "It is worse".Olivera said:
Equus, some excellent posts there.
Even expensive spaceframe kit-cars often have torsional rigidity a factor of ten less than mundane monocoque cars! Oddly this never seems to be discussed in kit-car circles...
It's regularly discussed in kit car circles. Space frames are at least as much about ease of fabrication than they are about performance. Note that it's also quite possible to build a poorly performing monocoque, just look at the MK1 MX-5. Wet paper bags spring to mind.Even expensive spaceframe kit-cars often have torsional rigidity a factor of ten less than mundane monocoque cars! Oddly this never seems to be discussed in kit-car circles...
Edited by Mr2Mike on Tuesday 3rd May 18:32
Mr2Mike said:
Stating that it's definitely less than other similar cars when you really don't know is poor form don't you think?
Sorry, I think you may have been (understandably) misinterpreting my response. It was confusing.I was reading ikarl's questions to run on from one another:
"How much torsional bracing does it have?... how much does it need? ...does it have more or less than other 'similar' cars?"
Therefore the question I was answering was "does it have more or less {torsional bracing} than other 'similar' cars'.
To which the answer, I think, remains a very clear 'less': there is a distinct absence of any tubes obviously intended to specifically provide torsional bracing. And that's why I qualified my answer by explaining where the bracing would normally be found on 'similar cars'.
You had, I think, read onwards from my mention of torsional stiffness in the answer to the previous question, and were reading that I was suggesting that the Exocet had less torsional stiffness?
I agree that the answer to that question would be based on opinion and likelihood, rather than being so definite.
Mr2Mike said:
Space frames are at least as much about ease of fabrication than they are about performance. Note that it's also quite possible to build a poorly performing monocoque, just look at the MK1 MX-5.
Spaceframes are about stiffness:weight ratio; which is, indirectly, still very much about performance. Cost and repairability are also a major considerations.They're actually pretty tricky and time-consuming to fabricate, compared to some of the alternatives.
A really good spaceframe for a 'Seven' type car, without cage, shouldn't weigh more than about 70kg, and should give a torsional stiffness of circa 2,700 - 3,500Nm/degree.
Even the poor old MX5 is considerably stiffer, in absolute terms, than most uncaged, open-top kit-car spaceframes (about 6,000 Nm/deg, so double), but it's nothing like as light (I've seen figures of 260kg for the bare shell).
Of course, there's a very good argument to say that because the overall weight of the car is lower, something like a Seven doesn't need as much chassis stiffness, anyway.
Edited by Equus on Tuesday 3rd May 20:16
Equus said:
The only thing that frightens me off buying one myself is that they necessitate an extremely dodgy approach to IVA, and it would be just my luck that I'd buy one, spend 2 years building it, then find that there's a clampdown on blatant abuses of the IVA test and I'm unable to register it.
What elements it dodgy on? I've been looking wistfully at Westfield XIs for a while. kambites said:
What elements it dodgy on? I've been looking wistfully at Westfield XIs for a while.
You want the full list?! I'm going to start looking like some evil assassin with a vendetta against kit cars, which is honestly not the case at all - I really do love the Westfield XI.
But for what it's worth:
- Front Lights (you IVA it with temporary 'frogeye' light pods.
- Aeroscreen (you IVA it without the aeroscreen fitted)
- Steering wheel (you IVA it with a temporary, compliant wheel, 'cos a 'period' looking one is non-compliant)
- Wing mirrors (ditto to the steering wheel)
- Doors (you IVA it without them fitted; the hinge and latch mechanisms are non-compliant, IIRC)
- Seats (you IVA it with temporary, high-back seats to give the correct height of head restraint)
- Rear lights and number plate (you IVA it with a temporary 'trailer board' that gives you fog light, reversing light, reflectors, compliant (vertical) number plate and number plate light).
- If you want to run wire wheels, those need to be added later, too.
Equus said:
Mr2Mike said:
Stating that it's definitely less than other similar cars when you really don't know is poor form don't you think?
Sorry, I think you may have been (understandably) misinterpreting my response. It was confusing.Equus said:
Spaceframes are about stiffness:weight ratio; which is, indirectly, still very much about performance. Cost and repairability are also a major considerations.
I agree that a spaceframe is primarily a performance oriented solution when designed and built toward that goal, but in the context of many low end kit cars and home built cars it's an easy and convenient way to tie the major parts together and provide mounting surfaces for bodywork. A ladder chassis is easier to build, but then you still have to fabricate extra supports to mount stuff (MDF/Plywood in the case of the Locust).Mr2Mike said:
...despite the lack of bracing on the MEV it does have large diameter tubes running the length of the car (albeit bent) which themselves will contribute to torsional stiffness.
The side trellises only contribute anything to the stiffness if they are linked by suitably stiff transverse bulkheads and bracing. Which, on the MEV, they're not - that's the whole point.
Equus said:
You want the full list?!
I'm going to start looking like some evil assassin with a vendetta against kit cars, which is honestly not the case at all - I really do love the Westfield XI.
But for what it's worth:
Pretty standard IVA dodge list that, isn't it? I'm going to start looking like some evil assassin with a vendetta against kit cars, which is honestly not the case at all - I really do love the Westfield XI.
But for what it's worth:
- Front Lights (you IVA it with temporary 'frogeye' light pods.
- Aeroscreen (you IVA it without the aeroscreen fitted)
- Steering wheel (you IVA it with a temporary, compliant wheel, 'cos a 'period' looking one is non-compliant)
- Wing mirrors (ditto to the steering wheel)
- Doors (you IVA it without them fitted; the hinge and latch mechanisms are non-compliant, IIRC)
- Seats (you IVA it with temporary, high-back seats to give the correct height of head restraint)
- Rear lights and number plate (you IVA it with a temporary 'trailer board' that gives you fog light, reversing light, reflectors, compliant (vertical) number plate and number plate light).
- If you want to run wire wheels, those need to be added later, too.
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