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Author: Subject: What is the lightest "7"
daniel mason

posted on 2/4/15 at 08:56 PM Reply With Quote
Pretty sure Steve marrs Saxon (if that's what sans refering too) is under 260kgs but that's unreal!
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Sam_68

posted on 2/4/15 at 09:45 PM Reply With Quote
quote:
Originally posted by daniel mason
Pretty sure Steve Marrs Saxon (if that's what Sam's referring to) is under 260kgs but that's unreal!


Yes, it's the Saxon I was referring to. I don't know if it's gained weight with middle-age spread (cars are as prone to doing so as humans!), or how accurate the original figures were, but when first unveiled in the hands of Rob Barksfield it was quoted at 208kg.

But unreal in what way? Surely it just shows what can be achieved if you're really obsessive about weight saving?

Even lighter would be possible with a smaller, lighter engine...

You don't necessarily need carbon fibre and bottomless pockets, either:

It's probably unfair on the Force (and slightly disingenuous in an entirely truthful way) to point out that there's another hillclimb single-seater out there that was knocked up in a domestic garage out of plywood and aluminium, with a car engine and gearbox, and built without even benefit of power tools, yet still only tipped the scales at 266kg.

More realistically, plenty of Jedis are sub-300kg, even with 4 cylinder, litre bike engines and despite old-school steel spaceframe chassis. The early, 2-stroke Jedis were well sub-300kg.

In that context, 307kg for a carbon-tubbed BEC single seater starts to look almost lazy.

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TimC

posted on 3/4/15 at 06:07 AM Reply With Quote
I think you'd get close with a Live axle striker with a basic roll cage and lightweight ali and GRP panels plus Braid/Force wheels and no fripperies.






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compturbo

posted on 8/4/15 at 12:59 AM Reply With Quote
quote:
Originally posted by Sam_68
quote:
Originally posted by daniel mason
Pretty sure Steve Marrs Saxon (if that's what Sam's referring to) is under 260kgs but that's unreal!


Yes, it's the Saxon I was referring to. I don't know if it's gained weight with middle-age spread (cars are as prone to doing so as humans!), or how accurate the original figures were, but when first unveiled in the hands of Rob Barksfield it was quoted at 208kg.


208kg

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daniel mason

posted on 8/4/15 at 06:27 AM Reply With Quote
Most jedis are over the 300 kg mark,and the SWB versions are tiny in comparison to the force! The penalty you pay for the attempted low speed downforce is the weight of the huge wings and the mounting structure.
Almost all the carbon tubed cars are circa 300 kg with fuel and fluids on board,but some are just getting under that figure now! The new GWR 1100 will no doubt be light but not seen any figures yet!
I've also just shaved around 6kg off the car so edging closer to the 300 mark

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Sam_68

posted on 8/4/15 at 07:14 PM Reply With Quote
quote:
Originally posted by daniel mason
Most jedis are over the 300 kg mark,and the SWB versions are tiny in comparison to the force! The penalty you pay for the attempted low speed downforce is the weight of the huge wings and the mounting structure...

Yes, most (though not all) modern Jedis with their relatively large, 4-stroke engines are over 300kg, but not by much. When I were a lad, they had 350cc or 500cc 2-strokes, and you could tuck them under your arm and carry them home at the end of a day's hillclimbing.

But even these days and in stock, circuit racing trim, with a 1 litre engine, they're still only about 325kg, and that's with a steel spaceframe chassis and relatively low budget, low-tech componentry. They're very much a single-seater analogy of the Sylva Striker, in that respect.

But I think more than anything, it just demonstrates that if you're serious about prioritising low weight as a key design factor, then:

a) You need to be ruthless about everything else. It's no good saying that 'it's quite light for a big car with lots of aero', because all that means, in absolute terms, is 'it's quite heavy'.

b) It's about more than just the chassis weight. The weight difference between the 208kg Saxon or the 249kg (wet lay-up) Megapin and the 300Kg+ Force is much more than the total weight of the chassis. You could make make the Force's chassis out of woven helium, and the car would still weigh a lot more than the Saxon.

It takes more than a carbon tub to make a light car...

Similarly, and back on topic, the lightest seven chassis I know of (the FW400's carbon tub) was quoted at 45Kg. You'd have to come up with a pretty inept spaceframe design to go much more than 75kg. So without getting silly (though, to be fair, it would be possible to design a tub that's a few kilos lighter than the FW400, if you really tried) that's a maximum of 30kg to be saved on chassis weight. Any other savings have got to come from somewhere else.

I agree with Tim that a Striker chassis with well chosen weight reductions in other areas would be the best bet for a really lightweight 'Seven' at sensible money.




... but am I the only person left in the world who doesn't break out in a cold sweat at the thought of driving a car without 30 kilos of climbing frame bolted to it as insurance against an event that almost never happens?

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daniel mason

posted on 8/4/15 at 07:27 PM Reply With Quote
Without knowing the car it's very difficult to pass comment on it! Unless you do?
Anyway it's not been an 1100cc class car as it was 2nd place car (I think) in the Scottish hillclimb champs outright, behind the Gould of Ross Napier, and had a 1000cc turbo motor installed before I bought it. Therefore the brakes are massive (and will shrink In time) and weight saving was never much of an issue at 330kg and 300 RWHP of holeshot turbo behind the driver!
It will eventually break the 300kg barrier which again is not mega light compared to the Saxon which is actually 224kg but still very similar to the the 300kg empires rolling out of bill chaplins workshop and breaking 1100cc records!
I'll be hopelessly slow though I imagine.at least until I get used to true single seaters after owning a truly lardy 470kg radical

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Sam_68

posted on 8/4/15 at 07:41 PM Reply With Quote
Nobody is disputing that heavier cars, with more power and/or more aero, can be very quick.

But that's not the point in question on his thread?

But we digress even talking about single-seaters. You expressed the opinion that a 370 kilo 'Seven' would be very difficult, on the basis that your carbon single seater weighs 307kilos... my argument would be that your carbon single seater is a poor benchmark, because it isn't that light in absolute terms.

I would be fairly confident that 370 kilos would be within reach of a very carefully specced 'Seven' (probably a Sylva derivative), even with a conventional spaceframe chassis.

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daniel mason

posted on 8/4/15 at 07:56 PM Reply With Quote
Fair point. But I don't currently know of any under 400kgs.
I know terry everalls westy is very well sorted,Planned,and specced. And covered in carbon and it's around 410kg I think

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Sam_68

posted on 8/4/15 at 08:48 PM Reply With Quote
Well, it is a wide-track SEi, which means it's physically a big bugger (I rattle round in one, and sylph like I am not!); probably +15 kilos on a Sylva, right there and then, no matter what else you do.

Then there's the full cage (25kg?).

The anti-roll bars and links (6 kg?)

Wide wheels (not saying they don't make it quicker, but they make it heavier, too)... pick a number, but let's be conservative and say a kilo a corner; 4kg total?

We're at 360kg, already, and we're not even trying yet!



I think we're getting too used to 'Sevens' that have been built for big power, and beefed up to suit.

Food for thought: over half a century ago, the state-of-the-art in front-engined 'Clubman'-type road cars like the Lola Mk. 1 and Lotus 17 - direct-line decedents of the original Seven - could weigh as little as 340 kilos, with a car engine and gearbox. Their steel spaceframe chassis could be as light as 25-27 kilos (against 45kg for the Westfield FW400's CFRP monocoque and typically 70 kilos for a modern 'Seven' type spaceframe, remember).

...and not a scrap of carbon fibre in sight.

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daniel mason

posted on 8/4/15 at 09:39 PM Reply With Quote
Would you drive at speed in competition with a car who's spaceframe chassis has the same quoted weight as a modern roll cage? I wouldn't.
Like Austin said, you could make them as light as you want within reason but the chances are it wouldn't be safe. I'd also suggest a striker,westy or s3 caterham would be the best bet for a lightweight 7

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Sam_68

posted on 9/4/15 at 06:39 AM Reply With Quote
quote:
Originally posted by daniel mason
Would you drive at speed in competition with a car who's spaceframe chassis has the same quoted weight as a modern roll cage? I wouldn't.


Yes, honestly I would, but I freely acknowledge that I'm not anything like as risk-averse as most people seem to be, these days - see my comment above.

In over a quarter of a century of driving 'Seven' type cars, I've never had an accident serious enough to rely on on a roll bar (much less a roll cage) or chassis impact strength to protect me. Its a therefore a risk that I, personally, find statistically acceptable.

Obviously, for competition there are other factors involved - the object is winning, and if that mean adding more weight to give you downforce, sufficient chassis stiffness to make your big, grippy tyres work well enough, or whatever, then if it will make you faster, you do it. But again, I think you risk confusing what's optimal for a particular application with what's possible.

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sam919

posted on 9/4/15 at 07:55 AM Reply With Quote
This is an intersting post, and ive chatted topics with Sam_68 before and i find you have become more amenable in the way you write :-), so consqeuently i find your posts very interesting and full of historical reference also interesting!

Anyway, ive been down the route of 300bhp duratecs and big power, the trouble is traction, so now for my new project a CBR like Terry E is using, but in standard form is the power source.

I need to achieve sub 400kg and with all the components needed to stop a heavier (heavier!!) 500kg car, this will be the start of the weight loss. Currently the only things left from the 500kg/300bhp days are the chassis with wishbones and roll cage. The brakes are smaller/lighter, the fuel tank is smaller/lighter, the wheels are smaller /lighter......etc etc.

As for the roll cage, it is the main component i cant really do anything about, its the double D superlight cage, and to be honest it will be getting left the way it is.

So whats the lightest 7......if a road going Whiting 7 can be 390kg then a race one you would have hoped be lighter, ok it was a 919cc carb version and live axle, but.....it has a dash panel, seat (i intend to use a foam version), more switchgear, paint! ali panels, ill be using carbon. If i get 390 ish but not over 400 ill be happy.

I feel the caterham 7 chassis which is a 2004 race item, is the lightest around and through numerous crashes over the years pretty sound in design if checked and maintained properly

[Edited on 9/4/15 by sam919]

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Sam_68

posted on 9/4/15 at 06:26 PM Reply With Quote
quote:
Originally posted by sam919
I feel the caterham 7 chassis which is a 2004 race item, is the lightest around and through numerous crashes over the years pretty sound in design if checked and maintained properly



For me, I think it would have to come down to whether I was building for road or race use.

The Caterham chassis is a lot heavier than the Sylva chassis (the best figures I have suggest possibly as much as 15 kilos), but it's also a lot stiffer (possibly getting on for double the Sylva's stiffness).

For race use, on relatively stiff springs, it may well be worth the weight penalty. For road use, where you will want the lightest springs and damping possible, to minimise skittishness over the bumps, ruts and potholes, chassis stiffness is much less of a factor (rule of thumb is that you need to be aiming at a chassis stiffness at least 10x your spring stiffness, so lighter springs = lower target chassis stiffness).


Whatever, I think you'll still be fighting a losing battle against traction, 'cos with ultra-lightweight cars (particularly those with no wings to give them 'pretend' weight), it becomes increasingly difficult to keep the effects of sprung:unsprung weight ratio in check. Top-notch damping helps, but you can only defy the laws of physics so far.

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sam919

posted on 9/4/15 at 06:56 PM Reply With Quote
I didn't think it was that heavier.

The car will be a race car, I prefer something a lot softer and more comfortable for the road.

Traction won't be an issue trust me, even with the potential forced induction it may well get later on, we have proven winning 'tech' behind the project as its an open class we race in.

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Sam_68

posted on 9/4/15 at 07:49 PM Reply With Quote
quote:
Originally posted by sam919
Traction won't be an issue trust me, even with the potential forced induction it may well get later on, we have proven winning 'tech' behind the project as its an open class we race in.


I'm struggling to imagine how it can not be an issue, though, unless the winning tech is some sort of anti-gravity device!?

The bottom line is that, no matter how good your damping, the inertia of your unsprung mass hitting any surface imperfection has to be transmitted to the sprung mass at a rate that would be damped out within, at most, 3 or 4 cycles of your suspension frequency. There's not much you can do, beyond a certain point, to reduce your unsprung weight, so the lighter you make the car, the more that inertia is going to degrade its grip.

The Caterham's nothing special in terms of unsprung weight, with that big de Dion beam (or even bigger live axle) and outboard brakes, so you're going to have a fundamental argument with the laws of physics?

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sam919

posted on 9/4/15 at 08:05 PM Reply With Quote
Think about F1 and its banned 'aids', even with limited regulation aero they still managed to get traction. I.e aero has nothing to do with it.
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sam919

posted on 9/4/15 at 08:13 PM Reply With Quote
Also the s3 lightweight race chassis is much lighter than a standard westy sei chassis bringing it closer to your sylva chassis weight, according to your above figures?!
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Sam_68

posted on 9/4/15 at 08:27 PM Reply With Quote
quote:
Originally posted by sam919
Think about F1 and its banned 'aids', even with limited regulation aero they still managed to get traction. I.e aero has nothing to do with it.


Traction control?

Well, fine, but it only gives you the amount of grip you have at your tyre contact patch?

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sam919

posted on 9/4/15 at 08:31 PM Reply With Quote
And a whole lot more!
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bi22le

posted on 9/4/15 at 08:32 PM Reply With Quote
quote:
Originally posted by gixermark
i had a road legal blade striker that was ~530-40 Kg, with full cage...

it had capri alloys.. and normal road bodywork, nothing fancy.. you could build one to 400Kg with thought and a few quid.

you could build a 36-380Kg 7, but for sure you would need to be creative... and spend a few quid


My 4age striker weighs 540kg with a normal half cage





Track days ARE the best thing since sliced bread, until I get a supercharger that is!

Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1

Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I

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Sam_68

posted on 9/4/15 at 08:35 PM Reply With Quote
quote:
Originally posted by sam919
And a whole lot more!


How?

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TimC

posted on 9/4/15 at 10:54 PM Reply With Quote
quote:
Originally posted by Sam_68
quote:
Originally posted by sam919
And a whole lot more!


How?


Elementary my dear Wat..ishetalkingabout?






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sam919

posted on 10/4/15 at 05:24 AM Reply With Quote
quote:
Originally posted by Sam_68
quote:
Originally posted by sam919
And a whole lot more!


How?


Electronics.

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Sam_68

posted on 10/4/15 at 06:40 AM Reply With Quote
quote:
Originally posted by sam919
Electronics.


Electronics just prevent the engine from delivering more power than the tyres can transmit to the tarmac. In other words, they don't give you a 'whole lot more' traction, they just allow you to make slightly better use of what's already there.

They can't possibly increase the amount of grip available at the tyre contact patch, which is basically a function of frictional coefficient and the load (mass and aerodynamic) on the tyre.

Ye cannae change the laws of physics, Capt'n.

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