Chassis strengthening for Chim/Griff
Discussion
I've made the decision to do a body-off chassis refurb, and wanted to get the collective opinion on what chassis bracing and/or modifications are possible to help improve chassis stiffness while it's all in pieces.
So the obvious starter is a half cage - not as good as a full cage, but it's gotta remain usable, and not some children's playground climbing feature to fit through...
I have heard of people adding additional bracing - and wondered what might have been done?
Is it simply extra triangulation/cross-bracing (if so, where?), or has anyone seen more involved modification?
Speaking to one of the Le Man's team many years ago, he said that the open unbraced nature of the chassis underside was the achilles heel - and the first thing they had done was add a solid tray to the bottom, and this has improved stiffness as well as aerodynamics...
So has anyone made changes to address the open underside? I did wonder whether adding some sort of removable brace might improve matters - perhaps like a longer, stiffer version of the exhaust mounting "tray", or some sort of similar bracing solution...?
Any thoughts, suggestions, or anecdotes etc much appreciated!
Dom
So the obvious starter is a half cage - not as good as a full cage, but it's gotta remain usable, and not some children's playground climbing feature to fit through...
I have heard of people adding additional bracing - and wondered what might have been done?
Is it simply extra triangulation/cross-bracing (if so, where?), or has anyone seen more involved modification?
Speaking to one of the Le Man's team many years ago, he said that the open unbraced nature of the chassis underside was the achilles heel - and the first thing they had done was add a solid tray to the bottom, and this has improved stiffness as well as aerodynamics...
So has anyone made changes to address the open underside? I did wonder whether adding some sort of removable brace might improve matters - perhaps like a longer, stiffer version of the exhaust mounting "tray", or some sort of similar bracing solution...?
Any thoughts, suggestions, or anecdotes etc much appreciated!
Dom
If you need to replace sections of the chassis then you could use CDS tube with the next tube thickness up. Would add stiffness and weight low down.
You might want to consider adding straps / tubes to fix the seat to rather than them being bolted to the thin body tub. Add another layer or two of GRP to the tube floor around the seats as well to stop flex as you get in or out.
As for the rest of the chassis then you copuld look at photos of the Challenge Cup and Speed 6 racers. You may want to check that there's nothing fitted in the space you want to put a brace.
A brace over the engine seems to be an obvious (from the laymans point of view) 'easy win' but likely to in the way come maintenance time.
Half cage is another 'easy win' but be careful of tube placement. I would allow for padded headrests and tube pads.
You might want to consider adding straps / tubes to fix the seat to rather than them being bolted to the thin body tub. Add another layer or two of GRP to the tube floor around the seats as well to stop flex as you get in or out.
As for the rest of the chassis then you copuld look at photos of the Challenge Cup and Speed 6 racers. You may want to check that there's nothing fitted in the space you want to put a brace.
A brace over the engine seems to be an obvious (from the laymans point of view) 'easy win' but likely to in the way come maintenance time.
Half cage is another 'easy win' but be careful of tube placement. I would allow for padded headrests and tube pads.
GreenV8S said:
Any particular problems or handling traits that you're trying to address?
If you want to keep the behaviour more or less the same then the obvious way to achieve that is to leave it alone.
No, it's just this will be the only opportunity to do this, as I don't plan on doing it again - so if there was a list of suggested modifications to help improve the infamous lack of rigidity, then this would be the time to assess and build into the plan.If you want to keep the behaviour more or less the same then the obvious way to achieve that is to leave it alone.
It always seemed to me that a half-cage with some forward braces coming down to the middle of the outrigger "lengths" might provide some protection in a side impact, while not impeding entry/exit too much...?
Edited by Dominic TVRetto on Monday 24th July 16:11
Biggest question for me is why are you wanting to go down this route ? What are you trying to achieve ?
If the car is so bad at the moment that it can literally be seen flexing then there are bigger issued with the chassis at hand. Otherwise I can't really see the point. Just my opinion of course, but the the potential costs and work involved won't come close to the possible benefits you may end up with in terms of it being a road car. Just not worth it I say.
I love my Chim to bits, but a dedicated track car that needs stiffening with various cages and bracing it isn't.
Only thing I would say is extra bracing for the seat anchoring points is a great idea. I've never been a fan of how they just bolt through the GRP. Would much prefer if they were through some decent metal and I'm fairly sure this has been done before so a search (here or google) would confirm that.
Your decision of course and I'm certainly not trying to rubbish the idea !! If you do go down this route would love to see the final product. Just my opinion again that I don't think its worth it or needed for the type of road car it is.
If the car is so bad at the moment that it can literally be seen flexing then there are bigger issued with the chassis at hand. Otherwise I can't really see the point. Just my opinion of course, but the the potential costs and work involved won't come close to the possible benefits you may end up with in terms of it being a road car. Just not worth it I say.
I love my Chim to bits, but a dedicated track car that needs stiffening with various cages and bracing it isn't.
Only thing I would say is extra bracing for the seat anchoring points is a great idea. I've never been a fan of how they just bolt through the GRP. Would much prefer if they were through some decent metal and I'm fairly sure this has been done before so a search (here or google) would confirm that.
Your decision of course and I'm certainly not trying to rubbish the idea !! If you do go down this route would love to see the final product. Just my opinion again that I don't think its worth it or needed for the type of road car it is.
Perhaps I should have used the word "stiffness" - if rigidity is different?
Loads of anecdotal feedback, Maclaren test rig story, analysis document PDF from the time TVR were developing the Cerbera (used to be available on MCS Software website, but unfortunately now unavailable).
Thanks all, keep them coming!
Loads of anecdotal feedback, Maclaren test rig story, analysis document PDF from the time TVR were developing the Cerbera (used to be available on MCS Software website, but unfortunately now unavailable).
Thanks all, keep them coming!
the only real way to stiffen a backbone chassis (other than a very comprehensive full cage) is to do what Gordon Murray's i-stream does and put sandwich panels bonded between the chassis tubes to brace them and reduce the flex, that's what they did on the T400's and Cerbera S12 I believe
Take a look at this https://www.sportmotive.com/tvr-evolution-chassis/ then give them a call I'd suggest to see if any DIY improvements are possible.
I seem to remember TVR working with a university (can't remember which one) on the Griffith chassis design to improve on the wedge design, which did flex noticeably, especially front to back. I think the Griffith has a pretty good chassis in my experience.
From a safety perspective, maybe attaching the seats to metal rather than fibreglass would be worthwhile, but I've never heard of any accidents in which a seat has come detached from the body or where such attachment would have made a difference - fibreglass is pretty strong!
I seem to remember TVR working with a university (can't remember which one) on the Griffith chassis design to improve on the wedge design, which did flex noticeably, especially front to back. I think the Griffith has a pretty good chassis in my experience.
From a safety perspective, maybe attaching the seats to metal rather than fibreglass would be worthwhile, but I've never heard of any accidents in which a seat has come detached from the body or where such attachment would have made a difference - fibreglass is pretty strong!
, but don't rigid things tend to break ? Englishman said:
From a safety perspective, maybe attaching the seats to metal rather than fibreglass would be worthwhile, but I've never heard of any accidents in which a seat has come detached from the body or where such attachment would have made a difference - fibreglass is pretty strong!
Two of the three TVRs I have where the seats are bolted to the GRP had cracked mountings. All the seats moved around alot as the tub flexed. All three had a floor thicknees of 3mm if that. Indeed, I heard one break as a 'powerfully built director' friend got in the car.Admittedly, the cars are used on track so the demands are different.
I'd use CDS over seam welded tube for repairs.
Englishman said:
I've never heard of any accidents in which a seat has come detached from the body or where such attachment would have made a difference - fibreglass is pretty strong!
I have. Which isn't surprising - seat mounts can take very high loads and these aren't spread out to the fiberglass at all well.I've got a set of seat brace bars under the floor of my V8S and it stiffens the seat up noticeably as well as probably being safer in the event of an accident. Mine clamp to the outrigger rather than being integral with the chassis.
You can weld in an additional tube from the top of the front shocker mount to as far along the first out rigger without fouling the wheel on full lock will definately help. This is a picture of a Cerbera but I have done it to the speed six chassis too which is in far greater need.
You could also weld on some mounting bobbins on to the spine in line with the out riggers which would make the tunnel more of a stressed member .
You could also weld on some mounting bobbins on to the spine in line with the out riggers which would make the tunnel more of a stressed member .
It just isn't going to be feasible to do it yourself, and even if you could, you are going to have to declare it to the insurers. I cannot imagine many/any would want to cover you when you've altered the chassis yourself based on some hearsay from some Le Mans team member years ago, and some apparent research that was once online, but isn't any longer.
And a roll-cage always looks awful on a road car that never had one originally, nor was designed for one.
Someone mentioned the Sportmotive Evo chassis. Read their website about it: https://www.sportmotive.com/tvr-evolution-chassis/
They seem to have done actual research, and changed many parts including hubs, brakes, wishbones, dampers, materials, shapes, tube size.
I don't know how many they have actually sold, or whether their website is up to date or whether the near £20K including VAT for a chassis is a standard or Evo one, or what that includes.
That's a lot of money to spend on an old Chimaera. Money you would never recoup. It's a classic car now, and it gives a classic car driving experience. That's why people but them. It was never the most rigid or sharpest handling car when it was new, 30 years ago. You might improve the chassis, but that will simply highlight another baked in or age related issue.
And a roll-cage always looks awful on a road car that never had one originally, nor was designed for one.
Someone mentioned the Sportmotive Evo chassis. Read their website about it: https://www.sportmotive.com/tvr-evolution-chassis/
They seem to have done actual research, and changed many parts including hubs, brakes, wishbones, dampers, materials, shapes, tube size.
I don't know how many they have actually sold, or whether their website is up to date or whether the near £20K including VAT for a chassis is a standard or Evo one, or what that includes.
That's a lot of money to spend on an old Chimaera. Money you would never recoup. It's a classic car now, and it gives a classic car driving experience. That's why people but them. It was never the most rigid or sharpest handling car when it was new, 30 years ago. You might improve the chassis, but that will simply highlight another baked in or age related issue.
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