Quantifying chassis stiffness...
Discussion
OK chaps,
So something that I have been wondering for a while, seems to be being discussed quite a bit at the moment - so I thought I would broach it as a topic...
So how stiff actually are the griffith/chimaera chassis..?
We've all heard the story about the Maclaren test rig - but what other cars had they had on the rig previously to compare it to, I wonder..?
How do these cars compare to your average modern eurobox - I know cars such as the Focus are supposed to be very stiff, but how does this translate into figures? And is the "average" eurobox as stiff as a Focus..?
Just really trying to find out how the cars match up to todays standards - and actually how noticeable any shortcomings will be on the road to an average driver?
Facts, figures, seat-of-the-pants opinions all welcome
Dom
So something that I have been wondering for a while, seems to be being discussed quite a bit at the moment - so I thought I would broach it as a topic...
So how stiff actually are the griffith/chimaera chassis..?
We've all heard the story about the Maclaren test rig - but what other cars had they had on the rig previously to compare it to, I wonder..?
How do these cars compare to your average modern eurobox - I know cars such as the Focus are supposed to be very stiff, but how does this translate into figures? And is the "average" eurobox as stiff as a Focus..?
Just really trying to find out how the cars match up to todays standards - and actually how noticeable any shortcomings will be on the road to an average driver?
Facts, figures, seat-of-the-pants opinions all welcome
Dom
A simple lay mans test is to jack the chassis up under one of the front suspension mounting points (say nearside) and see when the drivers door will still open and close as the chassis twists. Not very scientific but pretty obvious if you have only lifted the chassis a couple of inches when it all goes to pot.
Some "interesting" conversation about chassis stiffness a few posts down on this thread, if you've not already seen it?
phillpot said:
Some "interesting" conversation about chassis stiffness a few posts down on this thread, if you've not already seen it?
A very good link was buried away there, it answers plenty questions regarding stiffness from an analysis document from the time TVR were developing the Cerbera.http://www.mscsoftware.com/support/library/conf/wu...
Perversely there does seem to be an obsession with stiffness, I remember reading this years Autocar Handling day special!
Many modern cars can use a massively stiff (and heavy) frame to allow stiffer springs and dampers to reduce roll/pitch even though they have very bad weight distributions (am thinking RS Audis here!).
The problem with a convertible TVR is the harder the springs/dampers get (to combat roll), the higher the % flex in the chassis becomes, as with less give in the suspension, the more the chassis absorbs.
Roll can be reduced without changing springs/dampers, using roll centre heights and different anti roll bars. This is what the latter t-cars do. Griffs with these adjustments are in the latter stages of development and due to appear this year
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RedSpike66 said:
So are the Tuscan Challenge cars much much stiffer than a Sag chassis then ? As they only do balls out track days on sticky tyres ??
Read the PDF as per above. Basically yes though and from that PDF about by a factor of two!
It is because a racing car doesn't need to be as easy to get in and out of, so large cross sections of tubs in the way of getting to the seats help quite a lot.
RedSpike66 said:
So are the Tuscan Challenge cars much much stiffer than a Sag chassis then ? As they only do balls out track days on sticky tyres ??
Not an accurate measure, but mine's on axle stands right now as I'm swapping the motor, and the height of each stand has to be spot-on as there's no 'flop' in the chassis. Very easy to put it on 4 stands (at the corners of the outiggers) and find it's only being supported by 3. Push down on the 'lifted' corner and the other corner lifts. That's not to say it's particularly stiff compared to anything else, but there's no discernable flex just lifting the thing up by any corner. And of course that's just a measure of flex from the outriggers - not from the suspension pick-ups.RichardD said:
Read the PDF as per above.
Basically yes though and from that PDF about by a factor of two!
It is because a racing car doesn't need to be as easy to get in and out of, so large cross sections of tubs in the way of getting to the seats help quite a lot.
I very much doubt its anywhere near double, and not sure what you mean by large cross sectional tubs?Basically yes though and from that PDF about by a factor of two!
It is because a racing car doesn't need to be as easy to get in and out of, so large cross sections of tubs in the way of getting to the seats help quite a lot.
the cage in a tuscan challenge car is actually fairly rubbish in terms of additional strength.
my old griff chassis used to twist after I fitted the ajp lump into it, when backing off you could feel the back end lifting in one corner, Jason at str8six commented on it by calling it an animal of a car after he first drove it, would be interesting to see what the chevy engine installers are doing with the chassis, are`nt Sportmotive offering a different or beefed up chassis.?
considering the hieght of the chassis I think its a remarkable structure, when you look at where the chassis narrows in width from the gearbox area towards the rear diff you can see why with a lot of power and sticky tyres, the chassis would twist between the front and rear wheels, I would imagine a tuscan challenge car would not have this problem with a full roll cage fitted, this giving a lot of extra strength to the chassis by increasing its hieght, and also the bracing half way up the doors along the sides of the car, which would strengthen up the narrow area near the diff.
not an expert, but just my opinion, or guess.
considering the hieght of the chassis I think its a remarkable structure, when you look at where the chassis narrows in width from the gearbox area towards the rear diff you can see why with a lot of power and sticky tyres, the chassis would twist between the front and rear wheels, I would imagine a tuscan challenge car would not have this problem with a full roll cage fitted, this giving a lot of extra strength to the chassis by increasing its hieght, and also the bracing half way up the doors along the sides of the car, which would strengthen up the narrow area near the diff.
not an expert, but just my opinion, or guess.
Graham said:
I very much doubt its anywhere near double, and not sure what you mean by large cross sectional tubs?
the cage in a tuscan challenge car is actually fairly rubbish in terms of additional strength.
That should have been tube, sorry!the cage in a tuscan challenge car is actually fairly rubbish in terms of additional strength.
I suppose that analysis document was a study and in real production, the quality of metal used by TVR ended up being different (as per your comments)!?
There was a brief article in Autocar a few years ago where a Tuscan II was against a newish 911 and they preferred it on this particular (twisty and not smooth) section of road. That surprised me as I thought that the far far stiffer 911 (body rigidty) would have fared better, but seems as though the 911 had too hard suspension and the T2 was very well resolved. This without them complaining that the car was too wallowy or soft either
.TA14 said:
At a 30%+ increase in strength a roll cage is one of the best strength to weight modifications, a lot better than fitting bigger sections.
Agreed a cage can add significant stiffness. But you can improve significantly with a better design than the stock tc cage. The rollcentre cage as used in the tc chassied sags is much better. 
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