Chassis Stiffness

[Robert Lawrence]

Hi, Does anybody have figures on the chassis stiffness of the original GT40's, and the later replicas, be they space-frames or monocoques??
Robert Lawrence

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[Peter D]

Hi Robert,

I have a DRB GT40, & in Australia we need to meet some pretty tough regs as the GT40's are treated as brand new cars (have to meet all current design rules (except crash tests, thank heavens)).

The test results on the DRB (which exceed the rules by about 15-20%) are :

- Beaming Test : Max Deflection = 0.45mm
- Torsion Test : Torsional Stffness = 7250 Nm per degree

Kind Regards,

Peter D.

[Robert Lawrence]

Thanks Peter, how are the rules formulated??
Thanks

Rob

[Bob Putnam]

The original cars were approximately 10K Nm/deg., as are our ERA GTs. We'd be higher except that we narrowed the pontoons a bit for more interior room.

According to the RF web page their car is 20000 Nm/degree

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>The chassis has undergone torsional rigidity tests and has had, in excess of 20,000 Nm of force applied, the result was only one degree of deflection<HR></BLOCKQUOTE>

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> In this form the chassis would have an integrated roll-over bar<HR></BLOCKQUOTE>

Now in units I can relate to...

RF - 14,751 lbf*ft/degree
ERA - 7,375 lbf*ft/degree
DBR - 5,347 lbf*ft/degree

Of course it would be nice to know what the exact results were for the RF Australian road safety test without the roll cage so you can compare apples to apples. The testing method may also lead to different results, but for the two Australian cars I would guess that the method should be the same.

[Robert Lawrence]

Hi, some various comparitive figures I have found after a few hours exploration of my bookshelf:
GT40 Mk1: 12,500 lb-ft/deg (no bodywork fitted)
(Colin Campbell, Design of Sports racing Cars)
Lotus Elan: 5,000 lb-ft/deg
(Colin Campbell, The Sports Car )
Bearing in mind the weight of the car, quite an achievement..

And, from "Driving Ambition, the official inside story of the McLaren F1" by Doug Nye:
Porsche 959: 9,500 lbs-ft/deg
911 Turbo: 10,000 lbs-ft/deg
Lotus Esprit SE Turbo: 4,300 lbs-ft/deg

Mc Laren F1: the production minimum working target was noted as 8,000, with other references to 10,000 lbs-ft/deg.
No final production figure is given.

A comparitive figure could be to divide by stiffness by the vehicle running weight, and the wheel tracks of the vehicle.

Any thoughts from the masses?

Rob


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Talking with ray Christopher about this some time ago, he came up with a suggestion for individuals improving their owns cars torsional stiffness.

If you are ali panelling your tub yourself instead of a plastic tub, double skin around the chassis and then foam fill it. Will add a littel weight but Ray reckoned it would stiffen the chassis. No tests were done so still only a theory.

If done it would also add some road noise reduction and drummuing reduction which has to be a good thing.

However if you do this and fill voids where other things like pipes and wires pass through, then be warned that if you need to go back and change things it is hard work! GTDs use foam filling around the left fuel tank, and used to use it around the water pipes in the footwell.

Malcolm

[Bob Putnam]

Greg's right and "My bad"... Just goes to show you that my memory isn't what it used to be - and it wasn't too good to begin with. [img]images/icons/shocked.gif[/img]

12,500 lbft/deg=17,000Nm/deg

The ERA should be the same.

[Robert Lawrence]

I have spend some time ferretting around for various chassis torsional stiffness figures.
It is truly amazing how many cars apparently have "substantial" stiffness....a little like saying lots of power, or very shiny paint??
At any rate here is what I have found: but please be aware that because it has appears in print, does not guarantee it's accuracy!
Lotus Elise 111s: 11000 Nm/deg,
Dodge Viper Coupe: 7600 Nm/deg,
Ferrari 360 Spider: 8500 Nm/deg,
Lambo Murcielago: 20000 Nm/deg,
Audi TT Coupe: 19000 Nm/deg,
Latest Volvo S60: 20000 Nm/deg.
For those of you into Pickup trucks:
Chrysler Durango: 6800 Nm/deg
And apparently the current champion road car:
new Mini: 24,500 Nm/deg.

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