New Sportmotive chassis
Discussion
Anything that Ian at Sportmotive does is always worth the wait!
Most of you will know when he built my Griffith it took a lot longer than planned. He is always developing and trying to improve the Griffith/Chimaera and if I wasn't so delighted with the Griff I would be first on the list for the new Chassie.
Maybe in a couple of years!!
Most of you will know when he built my Griffith it took a lot longer than planned. He is always developing and trying to improve the Griffith/Chimaera and if I wasn't so delighted with the Griff I would be first on the list for the new Chassie.
Maybe in a couple of years!!
those look nice.
What have sportmotive done to the chassis ?
This guy explains what is wrong with the chassis .The chassis has been on the Mclaren Rig
http://www.youtube.com/watch?v=lqTbdmbL7mU
This guy explains what is wrong with the chassis .The chassis has been on the Mclaren Rig
http://www.youtube.com/watch?v=lqTbdmbL7mU
If you saw the evo chassis sitting next to a standard one you would see many detail differences. At the front, the top and bottom rails are wider apart to make more room for the LS3/T56 combo. There is a lot more bracing and triangulation everywhere. The shock top mounts are stronger and better located to put the shocks at a better angle. The rear anti-roll bar mounting is moved and integrated with the chassis rather than being stuck on underneath. There will be a longer closing plate underneath the gearbox/bellhousing area. The suspension is completely redesigned with all new uprights using the T car style 5 stud hubs. I could go on, but a lot of thought and detail improvement has gone into it. If you are really interested, you will have to visit Ian and let him show it you "in the metal".
The number of times I've heard Griffith owners past and present say how their Griff was scary down a twisty country road - then set it up properly would be my advice.
Put it another way. I can't think of a more difficult 12 mile stretch of road than the one from the Tan Hill pub near to Buttertubs Pass which runs to a little place called Reeth. Yumps are common place amongst the twists and turns, and by no means is the surface smooth at most all of its length, yet this road represents well how great the chassis is.
Frankly I think the Gordon Murray story is absolute b
ks. Maybe they did have a chassis on their rig but my bet would be that idiot in the video who looks like he's driving a bus rather than a sportscar was at the end of a long line of Chinese whispering.
Utter tosh!
Put it another way. I can't think of a more difficult 12 mile stretch of road than the one from the Tan Hill pub near to Buttertubs Pass which runs to a little place called Reeth. Yumps are common place amongst the twists and turns, and by no means is the surface smooth at most all of its length, yet this road represents well how great the chassis is.
Frankly I think the Gordon Murray story is absolute b
ks. Maybe they did have a chassis on their rig but my bet would be that idiot in the video who looks like he's driving a bus rather than a sportscar was at the end of a long line of Chinese whispering. Utter tosh!
500dread said:
Frankly I think the Gordon Murray story is absolute bks. Maybe they did have a chassis on their rig but my bet would be that idiot in the video who looks like he's driving a bus rather than a sportscar was at the end of a long line of Chinese whispering.
Utter tosh!
Actually the torsional stiffness is much lower than any current production car so the chassis test story may well be true.ks. Maybe they did have a chassis on their rig but my bet would be that idiot in the video who looks like he's driving a bus rather than a sportscar was at the end of a long line of Chinese whispering. Utter tosh!
IIRC a Griff chassis is circa 2650ftlbs per degree. Most modern cars will be multiples of this. The lowest I can think of are mass produced small sportscars like the MGF/TF and MX5 which are about double or more depending on the version.
However there is more to handling than just chassis stiffness, for one thing a TVR isn't that heavy so there is less mass to control and many fine handling kit cars are getting away with half the Griff value though admittedly with even less weight to control.
It does beg the question, if a guy that knew about engineering got to the point that he was measuring a Griff chassis then what was he trying to do with it? Perhaps he was trying to fit massively stiff springs or had got too accustomed to thinking that money-no-object carbon monocoques were "normal".
Before this gets a little too deep my point after watching the linked to video clip was simply how does someone like that idiot criticise a Griffith chassis for not being stiff enough. Because he could feel it? That I doubt.
I do note that when I jack up the Griff I don't see any noticeable flexing of the chassis. In fact the opposite is likely true. The car remains rigid. Yet jack some current production cars, I couldn't speak of all, of which you mention all are torsionally stiffer, I notice many will bend around the middle as a simple test of opening and closing a door will show.
But like you say, there is more to handling than just chassis stiffness. I just doubt the Griff chassis is not stiff enough as to be poor at its job as suggested by the road tester in that video. Also pretty much impossible to feel it isn't stiff enough unless compared directly to a modified chassis know to be much stiffer which can be felt when driven in comparison. I don't see that was the case for the road tester here or for Gordon Murray.
Seems to have drifted somewhat off the original topic..... It is intended that the Evo chassis will be torsionally stiffer than the original, but limitations inherent in a tubular backbone with a open top car mean it's never going to be as stiff as a modern GT. Unfortunately the TVR body design does not allow for anything structural in the sills. However, by redesigning the suspension with higher roll centres, (which TVR themselves did incrementally from one model to the next) hopefully we can use softer springs and put less twisting loads through the chassis. That's the idea anyway!!
I'll be seeing some more of my build next week. Maybe see if I can get some better pics....
I'll be seeing some more of my build next week. Maybe see if I can get some better pics....
cymtriks said:
Remember that torsional stiffness is measured from axle line to axle line or, near as makes no difference on a Griff, the spring mounting points, not from jacking points.
So you're saying if I jack my Griff up on the front cross member it'll bend more than if I jack it on the corner points of the outriggers?I'm still not seeing how a modern tin top jacked up so as the monocoque flexes can be torsionally stiffer than a Griff chassis. I've never noticed flexing or bending when I jack my Griff anywhere. That's a pretty good seat of the pants test for me compared to bending a saloon on a jack. You did say that ALL modern monocoques are stiffer didn't you? If this is true, and I've no reason to doubt your words (other than this is the Internet), you present me with a rather perplexing dilemma.
jwoffshore said:
It is intended that the Evo chassis will be torsionally stiffer than the original, but limitations inherent in a tubular backbone with a open top car mean it's never going to be as stiff as a modern GT
What are these limitations in torsional stiffness inherent in a tubular backbone chassis? In particular, compared to what when you speak of modern GT cars? 500dread said:
What are these limitations in torsional stiffness inherent in a tubular backbone chassis? In particular, compared to what when you speak of modern GT cars?
OK, I also have a Corvette Z06. I'm wondering what I'll think of it all when I "regress" back to the TVR!! The torsional stiffness of the Vette is about 10,000ft.lb/degree and a Porsche 911 is similar. As a result the difference in feel and responsiveness in cornering vs the Griff is night and day. I guess you could call the Porsche and the Z06 "modern GT's".In fact, here is table of typical car torsional stiffnesses in ftlb/degree
Locost: 1200 std / 2400 modified
Typical x-braced ladder 4"x2"x14swg: 1400
Lotus Elan incl body: 4300
Mazda MX5: 3800
Ultima GTR: 3300 std / 9500 modified
Lotus Elise: 7300
Porsche 911, Corvette Z06: 10,000
Corvette C6R (racecar): 28,000
There is a published student project report from Cranfield on the TVR chassis. The Griff comes out at about 2000 ftlb/degree for the chassis with gearbox plate and adding the body it goes up to about 2600. They then go on to look at the Cerbera chassis, adding roll hoops, Tuscan race chassis etc.
So there you see the Griff is not even as torsionally stiff as an old Lotus Elan. The Elise is considerably stiffer by virtue of its large ally box section sills, despite not having a fixed roof.
As for the Evo chassis, there is more bracing added to the backbone compared to the original Griff. The front end also has a lot more triangulation and hopefully it will also be possible to extend the gearbox plate to close the bottom of the backbone more effectively. But in the end, short of making it from carbon fibre, it's always going to be a struggle making a central backbone spine as stiff as a perimeter chassis or monocoque.
I think you've entirely missed the point.
Why does a road going Griff need to be any stiffer than it already is. Clearly it's been good enough for twenty years hasn't it?
If you're going to tell me a stiffer chassis is going to be faster from A to B than a correctly set up Griff then I'd say you would likely never know the difference unless you took such to the track.
Most of this bks has come about because people are pushing for silly numbers going for Chevy power as an example. It seems to me the excess power put through the chassis is the problem here and not the original design which now seems to be said to be lacking in torsional stiffness.
Away from any kind of track use a Chevy powered stiffer chassis Griff pushing silly big numbers is completely wasted on any road and won't likely go around corners or along an unclassified moorland road or a very twist A road any faster than a proper set up Griff in fine tune. And whilst I understand and embrace the quest for more power and harnessing it there comes a point where it becomes pretty pointless and that for me would be when such requires major modification or even replacement of chassis when a RV8 Griff can be made to go so well an average person could never really drive it to its full potential anyway.
One last point. Those numbers for the cars in your list. Did you ever consider they may well handle just as well with less stiffness? Do you know what the least amount of poundage is for those cars before their torsional stiffness becomes a handling issue? Much of the stiffness 'built in' to modern cars has more to do with collision strength than it does handling prowess.
And slightly not the same but Ducati have failed miserably to get near the podium since Stoner rode a tube framed flexing GP 800. Not even the GOAT himself could make way with the much stiffer carbon 'frame'. So much so Rossi had them bin it and mimic the factory Yamaha's twin spar alloy beam frame because it offered more flex allowing feel of what the front end does.
Why does a road going Griff need to be any stiffer than it already is. Clearly it's been good enough for twenty years hasn't it?
If you're going to tell me a stiffer chassis is going to be faster from A to B than a correctly set up Griff then I'd say you would likely never know the difference unless you took such to the track.
Most of this b
ks has come about because people are pushing for silly numbers going for Chevy power as an example. It seems to me the excess power put through the chassis is the problem here and not the original design which now seems to be said to be lacking in torsional stiffness. Away from any kind of track use a Chevy powered stiffer chassis Griff pushing silly big numbers is completely wasted on any road and won't likely go around corners or along an unclassified moorland road or a very twist A road any faster than a proper set up Griff in fine tune. And whilst I understand and embrace the quest for more power and harnessing it there comes a point where it becomes pretty pointless and that for me would be when such requires major modification or even replacement of chassis when a RV8 Griff can be made to go so well an average person could never really drive it to its full potential anyway.
One last point. Those numbers for the cars in your list. Did you ever consider they may well handle just as well with less stiffness? Do you know what the least amount of poundage is for those cars before their torsional stiffness becomes a handling issue? Much of the stiffness 'built in' to modern cars has more to do with collision strength than it does handling prowess.
And slightly not the same but Ducati have failed miserably to get near the podium since Stoner rode a tube framed flexing GP 800. Not even the GOAT himself could make way with the much stiffer carbon 'frame'. So much so Rossi had them bin it and mimic the factory Yamaha's twin spar alloy beam frame because it offered more flex allowing feel of what the front end does.
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