Torsional Stiffness assessments

[DavidTC]

The importance of a well designed chassis/monocoque is generally appreciated, yet there appears to be remarkably little validated data for the variety of designs used by the GT40 community, in provenanced quantitaive data for torsional stiffness for eample. In general we can categorise the prevailing approaches as 1) Those who provide figures where it is not clear what the metrology has encompassed.2) Those where the figures are calculated from the engineering design parameters but where actual validated measurement might reveal something different. Finally the 'finger in the air' brigade where there is a somewhat vague feeling that the design is stiffer than another because of this change in engineering design.
It could be I am alone in wanting to know more, and I know some of the manufacturers are starting to pay serious attention to validated measurements; but maybe there is more real data already out there than is apparent from a cursory view of some at least of the web/published info.
Anybody enlighten me ?.
David

 

[Mike Dozier]

David

There have been some good threads on this subject,
but I'm a failure as a thread "searcher".
Several of the companies we deal with provide test data on request...whether it was gathered properly I certainly
am not qualified to answer.

As someone who does not race, I confess I don't pay as much credence on stiffness figures as many others.
I rely more on input from those that have logged
lot's of miles on their car to demonstrate fitness of design. Like horsepower...you can do a lot of "bench racing"
comparing stiffness values....but to me the proof is
in the real world results.
Regards

Mike D

 

[Ron Earp]

David, there is another class on the board, the "just do it" crowd. If I was worried about stiffness on the race cars I have I imagine that I'd get discouraged and draw a bench conclusion that I could not race them. But, I do, and they work.

I agree with Mike, the stiffness of the chassis can definitely fall into the mental masturbation category as I doubt most people are going to tell the difference on track with a X stiff chassis to a 1.2X stiff chassis, provided both cars are setup properly for their respective differences.

But, on your question there are definitely a lot of folks who track and race their cars, especially GTDs. Ross in Australia races a GT40 that used to be an RF but he has made a lot of modifications to it so it is suitable for race duty. Don't know of any ERAs that are raced or CAVs, although Buzz's CAV has done the One Lap of America but that is far from racing. Might be some DRBs racing, not sure but I thought there was.

I doubt most of these folks have data collected in a controlled enviroment since they are just out doing their thing and making modifications as needed to correct issues. I've been on the board since the beginning and the only figures I've ever seen were some from RF, some from DRB, some GTD figures, and ERA, but none of them were collected using the same method so are essentially uncomparable. Maybe someone else has more info?

 

[DavidTC]

Guys
Thanks for the anecdotal feedback to date. I did a quick search of the threads BUT most of them were of the variety 'I jacked the car up on one corner and couldn't open the doors' variety. It's not an area to become obsessive about except when you notice that lack of stiffness is seriously affecting handling.It will be interesting to see what the query turns up amongst the pretty well informed community that this website encompasses.
Regards
David

 

[Mike Dozier]

David

RF40, DRB, and recently RCR have published
figures...yours for the asking...but whether they are comparable is a question mark.

Your comment about opening the door is interesting.
Both of my cars are easily supported by a jack on
only 3 corners....with no apparent sagging and certainly
no problem opening the doors. And my chassis aren't
anything special...basic tube frame (no cage) with paneling.
IMHO they are much more rigid than any mass produced car I've owned.

MikeD

 

[DavidTC]

Mike
Thanks for the feedback BUT the problem is that figures are bandied around BUT who certifies the measurement process?. In the US it might be NBS/ASTM all we need to know is who is the third party auditor?.
David

 

[Ron Earp]

Skip the figures. Get the car, drive the snot out of it, work on the areas that need attention. I don't think any of the figures collected thus far have an auditor (I might be wrong, but I bet no auditor that would satisfy those asking) nor were collected by third parties - basically all are useless for comparison to one another due to methodology (long thread on doing this yourself by someone). And, just a feeling, but I'm willing to bet all of them are stiffer than the original we all dearly love.

 

[DavidTC]

Ron
That's undoubtedly true BUT by how much ?.
David

 

[Mike Dozier]

David

The GT40 Australia website mentions their chassis was
tested under the "supervision of Government appointed professional engineers"....for whatever that's good for.
Paragraph says Test requirement was 6,000 NM per degree
and they achieved over 7,000 NM per degree.

In the the US there are no such requirements for individually constructed vehicles...it's pretty
much up to the individual Motor Vehicle Inspector's
judgement whether your chassis is road worthy or not.

MikeD

 

[DavidTC]

Mike
Many thanks; I suspected that if anywhere the Australian requirements would be the most stringent. I will follow up your lead.
David

 

'Paragraph says Test requirement was 6,000 NM per degree
and they achieved over 7,000 NM per degree.'

There is no argument, all ICV's must now pass. An individual building his own chassis now must front up the money and have the testing done. DRB has supplied the required paperwork that will be needed for the engineer's reports so the vehicle can be made street legal, in this state of New South Wales. I really dont see this as a problem - at least you know the chassis has been manufactured to a certain level of quality & strength. No 'bird-sh*t' welds here, thank you.


Les

drb #63

 

Chassis stiffness is not easely detected by the driver. A 7000N/mm chassis with an wheelrate of say 200p/inch has a fairly good distans from the 7000N/mm chassis stiffness to be detected by the driver. A 20000N/mm chassis will need
some 4-5Hz resonsce wheelrate before beeing noticable by the driver. The biggest diffrence using a stiff chassis is that we get better responce from shock and rollbar setting, as otherwise to large adjustments has to be made for the same effect.
For road driving 7000N/mm and 1,6-2Hz wheelrate (I would guess is common GT-40 setting) is more than adequate.
Regards
Goran Malmberg

 

[Peter Delaney]

As mentioned above, the Oz standard is 6000NM/deg for ICV's (Individually Constructed Vehilcles). But, if my memory serves me correctly (& that's a risk), there was a problem a couple of years ago when it was discovered that no clubman type cars could get near this figure. Expert advice was sought, & a revised figure of under 4000NM/deg was agreed here in the State of NSW. Horses for courses, I suspect.

Kind Regards,

Peter D.