What makes a good chasis?

[penski]

What would the GTM be with no roof ?

The Libra? It'd be a GTM Spyder 12000 Nm/deg...Still stiffer than the Elise

So far from irrelevant its not funny. The roof of any car is pretty integral to its stiffness. Were not talking yank cars here with chassis frames and body shells that drop on.

Think of a car with no doors on, the roof plays a huge role by thickening the section of the car massively!

The Elise follows in the tradition of the Elan, Europa et cetera - it has a SEPARATE chassis (with the suspension and engine mounted off subframes) and body panels hung off it. It is NOT a monocoque. The addition of a roof to the body panels would provide a marginal increase in stiffness.

Your comment about doors (as with your earlier comment) is irrelevant as we are not talking about a monocoque structure.

Retort?



*n

 

[Jonnycoupe]

But if Lotus were pursuing structural stiffness to include roof beams they most certainly would have used them in a structural role. Id like to hypothosise the optimisation of the chassis in such a manner would have meant they could have made a lighter stiffer chassis.

Is that figure for the S1 elise? CAE analysis has come a very long way since 96. Particularly if you can copy pin jointed frame structures with steel tube.

 

[penski]

Found some more data (copied verbatim):

Aston Martin DB9 Coupe 27,000 Nm/deg
Aston Martin DB9 Convertible 15,500 Nm/deg
Audi TT Coupe 19,000 Nm/deg
BMW E36 Touring 10,900 Nm/deg
BMW E36 Z3 5,600 Nm/deg
BMW E46 Sedan (w/o folding seats) 18,000 Nm/deg
BMW E46 Sedan (w/folding seats) 13,000 Nm/deg
BMW E46 Wagon (w/folding seats) 14,000 Nm/deg
BMW E46 Coupe (w/folding seats) 12,500 Nm/deg
BMW E46 Convertible 10,500 Nm/deg
Chrysler Crossfire 20,140 Nm/deg
Chrysler Durango 6,800 Nm/deg
Dodge Viper Coupe 7,600 Nm/deg
Ferrari 360 Spider 8,500 Nm/deg
Ford GT40 MkI 17,000 Nm/deg
Ford Mustang 2003 16,000 Nm/deg
Ford Mustang 2005 21,000 Nm/deg
Ford Mustang Convertible (2003) 4,800 Nm/deg
Ford Mustang Convertible (2005) 9,500 Nm/deg
Jaguar X-Type Sedan 22,000 Nm/deg
Jaguar X-Type Estate 16,319 Nm/deg
Lambo Murcielago 20,000 Nm/deg
Lotus Elan 7,900 Nm/deg
Lotus Elan GRP body 8,900 Nm/deg
Lotus Elise 10,000 Nm/deg
Lotus Elise 111s 11,000 Nm/deg
Lotus Esprit SE Turbo 5,850 Nm/deg
McLaren F1 13,500 Nm/deg
Mini (2003) 24,500 Nm/deg
Pagani Zonda C12 S 26,300 Nm/deg
Porsche 911 Turbo (2000) 13,500 Nm/deg
Porsche 959 12,900 Nm/deg
Volvo S60 20,000 Nm/deg

Rolls Royce Phantom: 40,000 Nm/deg
BMW E90: Supposedly 25% higher than E46, look above
BMW Z4: 21Hz... :scratch: Now I just need to figure out how to convert that...
Audi A2: 11900 Nm/deg
Audi A8: 25,000 Nm/deg
Audi TT: 10,000 Nm/deg (22Hz)
Golf V GTI: 25,000 Nm/deg
Chevrolet Cobalt: 28 Hz
Ferrari 360: 1,474 kgm/degree (bending: 1,032 kg/mm)
Ferrari 355: 1,024 kgm/degree (bending: 727 kg/mm)
Ferrari 430: supposedly 20% higher than 360
Renault Sport Spider: 10,000 Nm/degree
Volvo S80: 18,600 Nm/deg
Koenigsegg CC-8: 28,100 Nm/deg
Porsche 911 Turbo 996: 27,000 Nm/deg
Porsche 911 Turbo 996 Convertible: 11,600 Nm/deg
Lotus Elise S2 Exige (2004): 10,500 Nm/deg
Volkswagen Fox: 17,941 Nm/deg
BMW Z4: 14,500 Nm/deg
Ferrari F50: 34,600 Nm/deg
Lambo Gallardo: 23000 Nm/deg
Ford GT: 27,100 Nm/deg
Mazda Rx-8: 30,000 Nm/deg :eyepop: (hard to believe)
Mazda Rx-7: ~15,000 Nm/deg

So the Elise is 10,000 Nm/deg (open-topped)

And the S2 Exige is 10,500 Nm/deg (coupe)

And comparatively, the GTM Spyder is 12,000 Nm/deg (open-topped)

And the GTM Libra is 14,000 Nm/deg (coupe)

The comments about the elasticity of steel vs. aluminium is interesting...But a torsional test stretches, compresses and twists the chassis. I'd like to see how different materials perform...

*n

PS: The GTMs have 'composite chassis' ...But everyone knows they're fibreglass

 

[Nozzer]

Do remember the S2 Exige just has a roof bolted in. It isn't really structural.

 

[Jonnycoupe]

It will have a nice thick honeycomb core aswell. Composites are really moving things forward in all manner of engineeing applications. You have to question the cost implications when you apply it to a mass production role though. Most the established techniques employ use of the most versitile manufacturing tool, the hand mk1.

Just dont crash a Libra then i guess if you ever wanna use it again

 

[eidolon]

Until you bought your Elise I often wondered how much better the Elise was than the MR2. I always suspected that it was a league ahead but didn't want to cause an unjustified stir given how highly rated the MR2 is.

It's a lot better. Even though my MR2 had quite fancy suspension and stuff it still wasn't a patch on the Elise.

I haven't yet driven an Elise with Nitrons but I suspect that would make the Elise feel wallowy and soft. I'd better not drive one actually otherwise I can see £1500 disappearing from my account!

 

[Muncher]

It's a lot better. Even though my MR2 had quite fancy suspension and stuff it still wasn't a patch on the Elise.

I haven't yet driven an Elise with Nitrons but I suspect that would make the Elise feel wallowy and soft. I'd better not drive one actually otherwise I can see £1500 disappearing from my account!

Trust me mate, don't drive one with Nitrons, it will rinse your bank account.

Oh, and don't drive one with lightweight alloys and semi slicks either...

Or an Audi/Honda Elise....

Actually, don't drive anyone else's car just to be safe!

 

[penski]

Just dont crash a Libra then i guess if you ever wanna use it again

It has crumple zones and can be repaired

How much if you smash a shell or bend the chassis of an Elise?

Edit - the Libra has a lift-out roof panel too

*n

 

[Jonnycoupe]

You wouldnt have been able to do any sort of crash worthiness or certification with composites 10 years ago though. NDT testing and ensuring some sort of consistancy for a production run is still developing. Point about crashing one is that you wont know where several different types of hidden composite damage could have occured. Delamination of such a chassis really isnt something I'd like to think about and thats assuming a simple crash where the crumple zone does exactly what its supposed to. Huge impact loads from a wheel hitting a kerb should do enough to push most suspension inserts right through the chassis.

If you bend a Elise thats because you have data/metal showing that its wrote off or repairable. Composites is a different story altogether.

Does look a very complete package though, certainly that type of chassis is perfectly suited to a kit car/low production car. Supercharged B18 would be rather incredible in it.