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Discussion Starter · #1 ·
Have the issues on mounting a roll bar and harness for track days been addressed? At all the events where GM personnel and a Z06 have appeared, has the question been answered?

Thanks,

David

P.S.
I just keep on looking at the frame picture and think how much stiffer, safer, and more race ready the car would be if this had been addressed/installed at the factory.
 

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I talked to a GM engineer/management just this past weekend in Pontiac at an SAE event, and asked him that specific question. He said as far he knew the issue had not been resolved yet but they where still working on it. If I recall correctly, he also said that the most likely solution is a design that allows for bolting a steel roll cage that would be SCCA approved. I didnt press the issue as I was oogling a black C6 Z06.

Drew
 

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Discussion Starter · #3 ·
However bolting to an aluminum frame can be interesting...a track oriented car that can't be easily converted to the track...
 

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Any sportscar will often do well on a track. It's the nature of the beast so to speak. However, that does not imply they are "track oriented" by design or intent. The Z is a production street car and meets emissions and CAFE standards, amoung others. Period, end of story. It's no more "track oriented" than an Enzo, Carerra GT or any other relatively light, high horsepower, good tires and brakes, sportscar. In reality ANY car can be taken to a track. Some, like those mentioned, obviously do better on a track than your typical sedan, minivan or truck. The bottom line is they are all production street cars designed to be driven on public roads and meet the standards for such.

No manufacturer is going to build a street car with a rollcage designed to meet racing requirements. Although in some cases you will find a rollbar in order to meet safety standards regarding rollover protection, in the case of some convertibles for instance.

When I heard the new Z was going to have an aluminum frame one of my first thoughts was "How are they going to fit an SCCA T1 legal rollcage for example, ie: steel, to an aluminum frame since this currently requires welding?" The fact is it cannot be done, or at least not easily, and will require a bolt-in/on design as you alluded to. This presents some technical issues that, as you heard, are still undergoing consideration.

I talked about the possible rationale for using a hydroformed aluminum frame in the C6 Z06 in a post some time ago. I said that weight was most likely a factor in that decision and that it was necessary to reduce it as much as possible in order to achieve CAFE standards. Basically the lighter a car is the more horsepower it can have. Reason being it can run at a lower cruise RPM yet still achieve the fuel mileage necessary to meet the CAFE standard, whereas a heavier vehicle with the same horsepower would suffer in this regard.

I tend to think GM's rationale for this was marketing, pure and simple. By offering a vehicle with 500+ horsepower they are offering the enthusiasts (and I am certainly one of them) just what we want. But again, this comes at a price in terms of engineering it to meet certain criteria as mentioned above. It's a double edged sword so to speak. They meet the required criteria by keeping the weight down yet at the same time are able to market the car as having 500+ horsepower and light weight; relatively light weight certainly helping to improve overall performance, certainly a marketing advantage for a sportscar.

Here's another interesting point: it's well understood that drilled rotors offer no appreciable performance benefit. In fact they are a detriment as they tend to be more prone to cracking with hard use. So, why do you think GM is offering them? In my opinion it's simply for the fact the market perceives them as being "racier". Again, targetted marketing to the "high performance enthusiast", most of whom will never take their car to the track but want a car that looks like a "racecar". I call this the 'Walter Mitty syndrome'.

I'm sorry if that offends anyone but it's how I see it and I believe GM does as well.

Interestingly, the C6R does not use an aluminum frame. Why? Because they use C6 coupes as a starting point which do not have a hydroformed aluminum frame. They do however use C6 Z06 parts, or at least C6 Z06 looking parts, such as rear brake ducts, etc. My rationale being they needed a steel frame with which to construct the racecar and its integral rollcage. See where this is going?

I'm sorry to say it but I think the C6 Z06, like the C5 Z before it, is a marketing gimmick for lack of a better term. In the case of the C5 Z06 they took a car that by all accounts was not selling well (the hardtop) and found a way to market them by reducing weight, adding horsepower, and making a few other tweaks we're all familiar with. And they hit the jackpot with the "high performance enthusiasts". You have to give GM credit for that at least.

If you've read this far you're probably thinking i've got a beef with GM or that I have absolutely no clue what i'm talking about. However, you'd be wrong about both. Ok, maybe only the former. ;) But don't get me wrong on this: I own a slightly modified Z06 :lol: , and I love it! However, if I were to get a C6 Z I would do so with the understanding it is what it is, nothing more.
 

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No Doubt,
Thanks for a well written, well thought out, logical post; so much so that no one has taken up an argument. In the overall scheme of things, it is great that GM is offering such a product available at an affordable price, have a warranty, insurable, air, radio……blah, blah, blah. It is no deterrent understanding what it really is. If I am able to buy and enjoy one of these I will count it as a blessing.
 

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Hey David,

Educate me why a bolted rollcage/bar is so much more difficult to install than welded. Especially if the bolt mounts are OEM and already designed for proper structural integrity. Other than minor galling issues it seems to me just as easy if not easier to install, and leaves the option of uninstall.

One more question, don't the ALMS rules require a steel chassis? If so then isn't the issue of how the C6R is designed a rules issue not a design preference. After all racecars aren't designed to be 'right' they're designed to 'meet' the rules. I mean just look at NASCAR, the Z06 is only a few mods and racing slicks away from outperforming those POSs. Have you seen the suspension on those things?! Just cause some racing series build cars a certain way doesnt mean its more advanced or 'better performing'.

Cases in point: Here are a few more advanced designs that are outlawed, TCS, ABS, Active Suspension, Four wheel steer, Fiddle brakes, ground effects, and loading aero wings directly into uprights.
And I'm miles away from being exhaustive.

Drew
 

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I mean just look at NASCAR, the Z06 is only a few mods and racing slicks away from outperforming those POSs.
Don't take this wrong, i'm not a NASCAR fan by any means. However, to say a C6 Z is only a few mods away from outperforming a pupose built NASCAR car is patently absurd. If you mean pure performance and nothing else then yes. Although that would be a very narrow definition. When you take into consideration the safety criteria those cars have to meet while at the same time performing as they do then no production car is even in the same universe. One has to look at the total package and not just those factors they wish to compare.

The problem with a bolt-in rollcage is the rules currently forbid them, and for a reason: they are not as inherently strong as a welded cage. Even if the SCCA were to allow a bolt-in cage for the C6 Z06 I do not believe GM will include mounts for such. It would simply open a can of worms for liability reasons alone.
 

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I may be wrong but think that the Lotus Elise had a similar problem-(FRAME--Lotus designed lightweight structure of epoxy bonded aluminium alloy extrusions with integral steel seat-belt support structure and lightweight steel rear subframe) and SCCA has now approved it with a bolt in cage.
 

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No Doubt said:
Don't take this wrong, i'm not a NASCAR fan by any means. However, to say a C6 Z is only a few mods away from outperforming a pupose built NASCAR car is patently absurd. If you mean pure performance and nothing else then yes. Although that would be a very narrow definition. When you take into consideration the safety criteria those cars have to meet while at the same time performing as they do then no production car is even in the same universe. One has to look at the total package and not just those factors they wish to compare.
I didnt really mean that literally, but I think you got the point. Racecars are designed to be optimised to the rules not the current state of the art in design.

Like fcar says, I think there is an option for special SCCA approval for bolt in cages for the Z. Which is what GM seems to be pursuing.

I'm not convinced of your two arguments why Gm shouldn't go bolt:
1 Its not as safe.
2 Liability.

1.) Im not as trustworthy of all things welded, but maybe I'm just not experienced enough with welding. Furthermore, I think a really good bolt design can be just as strong as any weld. But thats just the issue, is it well designed? I think that may be one of the reasons why the SCCA doesn't want to go down the bolt road for everyone. They would either have to trust that everyone properly designed the setup, or do a rigorous tech inspection at every event that may lead to large number of people being rejected for not perfectly following the rules.

But if someone like GM can provide a good design with data to back up safety claims then it should work fine.

2) What liability? They will always be held responsible for manufacturing liabilities no matter what (at least legally they are supposed to be...), on highway or private property. So if they design and manu properly then they've done all they're expected to do; whatever stupid thing someone does with that machine is thier own stupid fault.


The question I asked was what added difficulties does bolt introduce vs welding in regards to installation as David hinted at. I would still like to know, this is a more practical application question that I'm a little ignorant about.

Drew

EDIT: Funny how a little word like 'dont' or 'not' in inserted into a sentence can completely change the meaning...
 

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Discussion Starter · #10 ·
Ooo...lotsa stuff.

NASCAR vs C6Z06...well Cup cars are around 800hp. However most late model asphalt stock cars are around 500hp & 2800-3000# with the driver. So, a little better than the stock Z06. They typically run 13" tires on 15x10 rims. Brakes are similar. Shocks are probably way better on the late model. Really, fairly close.

On the other hand a late model can bounce of the wall or another late model and keep on going. Or take a 120 or 140mph shunt that would leave a stock Z06 driver's spouse a widow(er).

For that reason, safety equipment in tracked cars is important.

Now to mounting steel safety equipment on aluminum structures. Yes, it can be done. However, it requires a mounting interface that spreads the load over a big area. When bolting a rollbar in to a steel unibody chassis, you need big plates at the mounting point. On both sides of the sheet metal.

When bolting to aluminum frame rails, you not only need to distribute the load over an even wider area, but need to support the internal structure of the aluminum. Otherwise the aluminum structure will just distort under load.

Why will it distort if it strong enough to make a stiff chassis? Because their are two factors: elasticity, which is how much it stretch/twist under a load that allows it to return to its original shape; and yield strength, which is the load that will cause it deform in a way that it won't recover.

A spring runs in its elastic range. All metal is formed by moving it past its yield strength. For a given elasticity, aluminium will have a lower relative yield strength than steel.

This is way you never find it in springs and structures that need to deform without yielding. But do find it in structures that should be stiff enough to have minimal elastic deformation (chassis, wheels, rocker arms). For connecting rods, it is only used in low cycle or low stress situations.

To mount even a rollbar will probably require extensive disassembly, large plates on top and bottom, and stiffening tubes between the plates. It may even involve boxing in steel the section of frame where rollbar mounts.

As to welding instead of bolting...welding joins the two metals as one, usually over a much larger cross sectional area. Bolts are limited in strength by the bolts cross section, can't go to edge of the mounting flange reducting leverage, and are always heavier, requiring the bolt in addition to the plate that would already be needed.

Back to stock cars. In stock cars, things you may think of bolting are virtually always welded. And the welds ground off/through to remove ('unbolt') the part. Lots of grinding disks on 4" and sometimes 7" hand grinding wheels. And a sawzall.
 

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Make one exaggeration on the internet and people never let it go... really I didnt mean the nascar comparison literally.

I understand how elastic and plastic deformation works.

What I was trying to say was that with the computational resources of a company like GM, a proper solid model of the chassis has already been made and so by importing and meshing in an FEA program will provide the necessary information arrive at equivelent design to welding by use of bolts instead. By using properly designed mounting points that would ensure the proper cross section required for the calculated shear stresses. And all that Jazz...

So if the mount is provided integral to the Z06 aluminum rails the mounting needed to bolt the roll cage/bar, then it seems installation should not be any more difficult than welding. But this is the part Im asking about, is there unforseen difference that is being overlooked by integral mounts vs welding that makes welding so much easier to install. The only one I can think of is that welding provides so much more flexibility of where to mount, but I should think that in turn provides more ways to screw up the setup. Integral mounts simplifies, and assures that thought has already been put into where these particular mounts are loading into (ideally some sort of chassis node, but thats more typical of tubular space frame)

Drew
 

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NoDoubt
I agree with most of what you said but I dont think the Zs are marketing gimmicks. The tuning they do actually works unlike many manufacturures. I mean Vipers GTS model a few years back was a joke as were some special model Vettes in the past. Grandsport comes to mind. The Ferrari 355 Fiorno is another. I would agree that many manufacturures special editions dont often make performance benifits but the C6Z is nearly a different car it has so many upgrades. Its almost a bigger difference than the 360 and 360 Stradale. Hard to call yet.
 

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No Doubt said:
Don't take this wrong, i'm not a NASCAR fan by any means. However, to say a C6 Z is only a few mods away from outperforming a pupose built NASCAR car is patently absurd. If you mean pure performance and nothing else then yes. Although that would be a very narrow definition. When you take into consideration the safety criteria those cars have to meet while at the same time performing as they do then no production car is even in the same universe. One has to look at the total package and not just those factors they wish to compare.

The problem with a bolt-in rollcage is the rules currently forbid them, and for a reason: they are not as inherently strong as a welded cage. Even if the SCCA were to allow a bolt-in cage for the C6 Z06 I do not believe GM will include mounts for such. It would simply open a can of worms for liability reasons alone.
Yeah you can't even begin to compare the performance of the Nascar to the Z. The Z would get spanked all the way around the track. Those things are like 800 hp and near 3K lbs.
 

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Discussion Starter · #14 ·
vettefan10 said:
So if the mount is provided integral to the Z06 aluminum rails the mounting needed to bolt the roll cage/bar, then it seems installation should not be any more difficult than welding. But this is the part Im asking about, is there unforseen difference that is being overlooked by integral mounts vs welding that makes welding so much easier to install. The only one I can think of is that welding provides so much more flexibility of where to mount, but I should think that in turn provides more ways to screw up the setup. Integral mounts simplifies, and assures that thought has already been put into where these particular mounts are loading into (ideally some sort of chassis node, but thats more typical of tubular space frame)
Yes, If the mounting points were designed in, it would be straightforward to bolt or glue the rollbar or rollcage to an aluminum or carbon fiber chassis. The Elise chassis is aluminum glued together. Aluminum and CF race chassis have had this for decades.

This is the core of the issue. Does the C6Z06 have mounting provisions? The answer appears to be no.
 
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