GT350 vs. Z/28

[thePill]

Whoa, whoa...

Yes, all Ring cars have cages. That won't change nor is Ford advertising one as of now.

Yes, there is a decent spread in similar models. Hell, there are even colors that are heavier than some. Anything Tri-coat or Metallic can be almost double digit differences.. So... Back in the deck.

If Ford releases a Ring time, the car doing the lap will be caged. Do you see Ford out here advertising caged laps as OEM capable? No...

The fact is, a cage would allow even the worst of platforms to perform. At this point, it would come down to cage design being a major factor in "official" Ring times. Like it or not, a cage has become a variable in Nurburgring lap times... and it is becoming a major one.

Has anyone considered the torsional forces applied to a structure at Ring speeds and Pony Car weight? Has anyone even considered that these cars wouldn't even be capable of said lap times IF the cage was absent altogether. The geometry changes on the suspension alone would alter the very character of the car. If it was merely a roll bar, then the advantage would be minimum. At lower speed, sure, it isn't as major. Nurburgring? Pony cars require cages as do most land vehicles under 8 flat.

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[Norm Peterson]

I'm sure you realize it's not as simple as "having a cage" vs "not having a cage" . . . and that if the suspension ride and roll stiffnesses on all these 'Ring cars holds any semblance to "stock" that the point of diminishing returns on added stiffness is reached sooner. The chassis (including any cage) is really just a stiffness matrix (loosely, a spring) that connects the front suspension to the rear suspension, and stiffening up one spring in series with two (or four) others doesn't fix any stiffness deficiencies in the others.

We don't know enough about any of these cages to conclude much with respect to performance improvement. It is quite possible to build a safe cage that doesn't add as much stiffness as people may want to think.


Norm

 

[thePill]

I'm sure you realize it's not as simple as "having a cage" vs "not having a cage" . . . and that if the suspension ride and roll stiffnesses on all these 'Ring cars holds any semblance to "stock" that the point of diminishing returns on added stiffness is reached sooner. The chassis (including any cage) is really just a stiffness matrix (loosely, a spring) that connects the front suspension to the rear suspension, and stiffening up one spring in series with two (or four) others doesn't fix any stiffness deficiencies in the others.

We don't know enough about any of these cages to conclude much with respect to performance improvement. It is quite possible to build a safe cage that doesn't add as much stiffness as people may want to think.


Norm

Nurburgring is probably the last track you would see diminishing returns in torsional rigidity. These cars have traction and grip now thanks to quality rubber and a hefty size. I witnessed the ZL1's rear suspension shimmy around the carousel, as I have seen numerous others do the same. That's the rear coming back into its own geometry, the spring you were referring to. Even with a cage full-tilt, the suspension still tries to diamond. This appears unavoidable... At this track, the Camaro benefits far more with cage installation than say a Corvette. In fact, a cage is probably the major factor that allows a Camaro of any kind to be time competitive with a Corvette.

The 5th Gen Camaro itself has most likely reached its own point of diminishing returns. The 8 minute mark was something special because it tested the actual structure. Sure, a cage will come to a point where no more gains can be had, and I'm sure a caged 5th Gen is getting to that point. However, I have extreme doubts it could achieve those times without one. The cage extended the structures original capabilities. There are currently no structures in this industry that are rigid enough to be immune to torsional forces. In every circumstance, there is always room for improvement, the table doesn't lie. Of course, the table isn't hitting a hairpin at 70mph either. There are a lot of cars on that list that probably wouldn't make it without some prep work.

Another downer is, just adding a cage... While many road warriors add one in for cosmetics, chassis guys know better. If you expect your Camaro to produce a mid-7 minute Ring lap, you can't just add a cage. Norm, we need to make some suspension adjustments to compensate. Merely slapping a cage onto a car will make any high tech and optimized suspension not optimal. We don't even need to go into detail about rear balance. An issue with running on an empty tank is that 52/48 turns into a 57/43. A cage would remedy that in an instant...

But anyhow, the suspension... Adding weight would alter the ride height for sure. The spring/strut rates would all need to be recalculated too and, perhaps camber. Who really knows... I know that changes would need to be made and we don't know what those changes are.

Many say that a cage doesn't matter, many that have no education in this area make these statements. The first thing they say is liability... Well, yes and no. There are countless other test at other tracks around the world that "liability" isn't as important. VIR, Sebring... Lots of fast tracks but no cages installed for these editors and such. The advantages of a cage are not as overwhelming on smaller courses, the weight and traction is still there but the speed isn't. Nurburgring though... speeds are doubled... which applies a force multiplier on the suspension and structure.

We just don't know...and unfortunately, that is a major draw for a manufacturer looking to market those times. Customers can never replicate them even with their best efforts.

I made a pretty big deal about the ZL1 running a cage. If it wasn't a big deal now, why is the actual z28 that ran the lap missing? I mean... It is totally MIA... Usually means they didn't want anyone to see it, especially people with trained eyes.

 

[Norm Peterson]

Nurburgring is probably the last track you would see diminishing returns in torsional rigidity. These cars have traction and grip now thanks to quality rubber and a hefty size. I witnessed the ZL1's rear suspension shimmy around the carousel, as I have seen numerous others do the same. That's the rear coming back into its own geometry, the spring you were referring to. Even with a cage full-tilt, the suspension still tries to diamond. This appears unavoidable... At this track, the Camaro benefits far more with cage installation than say a Corvette. In fact, a cage is probably the major factor that allows a Camaro of any kind to be time competitive with a Corvette.

My point is that with softish suspension settings - and compared to a serious race car the Z/28's suspension is still pretty soft - you get to a point where more chassis stiffness no longer improves the effectiveness of fine tuning efforts in the suspension. Beyond that point, you're just adding weight.

Were you able to separate tire tread movements relative to the suspension (at the stub axles) from the suspension movement relative to the chassis? Lateral tire deformations are huge, and potentially misleading.

The 5th Gen Camaro itself has most likely reached its own point of diminishing returns. The 8 minute mark was something special because it tested the actual structure. Sure, a cage will come to a point where no more gains can be had, and I'm sure a caged 5th Gen is getting to that point. However, I have extreme doubts it could achieve those times without one. The cage extended the structures original capabilities. There are currently no structures in this industry that are rigid enough to be immune to torsional forces. In every circumstance, there is always room for improvement, the table doesn't lie. Of course, the table isn't hitting a hairpin at 70mph either. There are a lot of cars on that list that probably wouldn't make it without some prep work.

How is the 8 minute mark anything more than a convenient number for what used to be an arbitrary goal? It's intrinsically a better feat than 8:01, but only by that one second. No new structural effect happens.

Structurally, there is no such thing as 'immunity to torsional loads' at any level, only stiffness values that can tell us how much or how little the chassis distorts under such loads (and strength values so we'll feel comfortable that it won't break any time soon). It's up to the chassis engineer and the rest of the development crew to

Another downer is, just adding a cage... While many road warriors add one in for cosmetics, chassis guys know better. If you expect your Camaro to produce a mid-7 minute Ring lap, you can't just add a cage.Norm, we need to make some suspension adjustments to compensate. Merely slapping a cage onto a car will make any high tech and optimized suspension not optimal.

So if a mfr is going to get called out for using a cage, perhaps the fact that a cage is present shouldn't be the only thing that gets harped on. Even if that only means once in a while mentioning that you suspect the suspension calibrations to be at least slightly "un-stock".

We don't even need to go into detail about rear balance. An issue with running on an empty tank is that 52/48 turns into a 57/43. A cage would remedy that in an instant...

I won't argue your weight distribution percentages, but the best a cage can do here is minimize the shift in actual roll couple distribution as fuel is burned off. It cannot fix the fact that the weight distribution changed, or do anything to maintain roll couple distribution in a constant relationship with weight distribution as the fuel load varies. Basically, a 55/45 TLLTD that might work nicely enough with a 52/48 weight distribution could well end up being too loose when the weight hits 57/43.

Yes, you can adjust roll stiffness distribution in a race car, but how many cars off the showroom floor offer that capability? How many owner-modified cars with adjustable-stiffness suspensions (typically dampers and sta-bars) offer on-the-fly adjustability?

Many say that a cage doesn't matter, many that have no education in this area make these statements. The first thing they say is liability... Well, yes and no. There are countless other test at other tracks around the world that "liability" isn't as important. VIR, Sebring... Lots of fast tracks but no cages installed for these editors and such. The advantages of a cage are not as overwhelming on smaller courses, the weight and traction is still there but the speed isn't. Nurburgring though... speeds are doubled... which applies a force multiplier on the suspension and structure.

The forces associated with 1g braking or 1g cornering at any given speed are not track dependent beyond differences in grade and camber. So aside from having to cope with truly unique features such as the Carousel or the length of that one straight, how would the 'Ring demand more from the car than other shorter but still fast tracks? More demanding on the driver I get.


Norm

 

[thePill]

My point is that with softish suspension settings - and compared to a serious race car the Z/28's suspension is still pretty soft - you get to a point where more chassis stiffness no longer improves the effectiveness of fine tuning efforts in the suspension. Beyond that point, you're just adding weight.

Ah, I get ya'... The suspension has most likely reached its limits. Which is why I do not trust the addition of structural support. As I mention previously, nobody, and I mean nobody, is going to plop a full cage in the car (150+lbs) while completely ignoring the balance changes without tuning the suspension up. It would make these cars skip across the corner like a stone on water. If I were about to make a record run attempt, the car would need to be flawless... Even in the Mustang, once it is caged the rear suspension needs work or it will lift the inside tire. As a Chassis Engineer, I wouldn't bother the suspension until all weight reduction has been complete, cage installed and race weight had been determined.

In order for even the Camaro's suspension to perform as it did, it would need to go well beyond it's OEM suspension capabilities. It would need to be stiffened... and this is where the cage comes into play... The suspension geometry and structural changes happen together. A soft suspension isn't going to save your structure from deformation. Suspension deforms differently than the structure and it isn't a static event. So, while the Camaro's suspension may not be keeping up, the additional reinforcement will ensure lateral changes are not made involuntarily. Neither of these issues are completely curable and neither of them are isolated. Both events occur and devolve rapidly and simultaneously. Without stabilizing one (the structure and most important) you can NEVER stabilize the other (suspension) or optimize your tires.

Were you able to separate tire tread movements relative to the suspension (at the stub axles) from the suspension movement relative to the chassis? Lateral tire deformations are huge, and potentially misleading.

Lateral movement is always on entry. The suspension movement you are referring to isn't a static event, it is ongoing and never ending. On entry, force is applied to the lead tire which causes that diamonding. Since the whole structure acts as a slinky, you will notice this diamond effect relax on exit. Hopefully, it isn't at every turn. One of the main areas this characteristic stands out is the carousel.

The geometry suspension changes that we are talking about is in almost every movement, even braking and accelerating. Of course, there are major events that will result in a spin. This is a much simpler issue to remedy... stiffen it up. When an OEM vehicle such as the Camaro, even in z28 form, comes along and shatters most exotic cars times, it gets me thinking. The suspension in these cars are NOT race ready. I don't think there is a suspension on any Pony Car right now that can perform at the Ring as advertised.

How is the 8 minute mark anything more than a convenient number for what used to be an arbitrary goal? It's intrinsically a better feat than 8:01, but only by that one second. No new structural effect happens.

This is where being at Nurburgring would help. Oh man, we are so led to believe anything... In real life Norm, 8 minutes on just a Bridge/Gantry lap is difficult. These are semi-race prepped cars and they still have issues.

This diamonding is also present on these ultra-high speed sweepers, through the Fox hole and on entry into every turn over 70mph. That is a big difference on this track, the speeds at which we enter make VIR look like Kindergarten. This is where the maximum torsional force is applied to the structure. Any time the suspension is set and you are getting grip, the next issue arises. This being lateral deformation of the structure. Now, keep in mind Norm. Soft suspension isn't preventing the structure from twisting, it is doing that regardless.

Structurally, there is no such thing as 'immunity to torsional loads' at any level, only stiffness values that can tell us how much or how little the chassis distorts under such loads (and strength values so we'll feel comfortable that it won't break any time soon). It's up to the chassis engineer and the rest of the development crew to



So if a mfr is going to get called out for using a cage, perhaps the fact that a cage is present shouldn't be the only thing that gets harped on. Even if that only means once in a while mentioning that you suspect the suspension calibrations to be at least slightly "un-stock".

I won't argue your weight distribution percentages, but the best a cage can do here is minimize the shift in actual roll couple distribution as fuel is burned off. It cannot fix the fact that the weight distribution changed, or do anything to maintain roll couple distribution in a constant relationship with weight distribution as the fuel load varies. Basically, a 55/45 TLLTD that might work nicely enough with a 52/48 weight distribution could well end up being too loose when the weight hits 57/43.

A caged z28 has a slight rear bias with an 8 point and a full tank. It is the most ideal out of all the Pony Cars.

The forces associated with 1g braking or 1g cornering at any given speed are not track dependent beyond differences in grade and camber. So aside from having to cope with truly unique features such as the Carousel or the length of that one straight, how would the 'Ring demand more from the car than other shorter but still fast tracks? More demanding on the driver I get.


Norm

The Ring...

I have never seen the speeds I have experienced at any track, than the speeds at Nurburgring. Even lane changes can be catastrophic... Structural torsion is multiplied by infinite variables. The two we are most concerned with at the Ring is our velocity and mass (weight). Of course, none of that would matter without the lateral grip these cars are capable of. The Ring is just a far better gear check than other track. It will test the structure unlike no other track in the world as well as everything else...

...and there ends my gripe... Keyword is "TEST" and hopefully make better. You are NOT making the car better by researching and developing a car with a cage in it. Norm... You are not going to convince me otherwise.

Marketing... "Marketing" has become the keyword for some... and in their endeavors, through the presence of competition and the lack of supervision, have begun working the system. The 8 minute mark was a special thing... it took a lot of chassis work to do it... Now, there are a lot of things left unchecked and unchallenged.

Chevrolet is the last manufacturer I would let go on integrity.

 

[Norm Peterson]

Pill, I spent most of my career as a civil/structural engineer involved with static and dynamic analysis, so even though the work wasn't automotive in nature I do have a pretty good sense of how structures respond to loadings and how things behave on a time basis.

I think the effects you're noting as being more evident (and potentially more dangerous) at higher speeds are at least as much a function of yaw damping dropping as a function of velocity as they are by increases in the rates at which these forces develop. And far more a function of yaw damping than chassis torsional displacement effects.


What's your guess for the Z/28's chassis torsional stiffness and the roll resistances of the front and rear suspensions? If you doubled the chassis stiffness, how much smaller would the torsional displacements be?


Norm

 

[thePill]

I can't guess on rigidity Norm, a table would be needed.

...I agree with the analysis Norm but, as I said, structure changes and suspension changes are two different things. Yes, some of that character you describe could be suspension oriented although, at the same time, structural changes are occurring too.

It's the same concept as patting your head and rubbing your stomach together. Both happen independently but, have a direct effect on the other.

I have witnessed at least one of the Ring Camaro's exhibit this "Spring Back" coming out of the carousel. The ass does a little Elvis mid-corner/exit and, as many know, those had cages (big time). This is more evident when thick tires are used because of the grip/slip shimmy coming out. If these cars are doing that with a cage, it would probably lose it in that particular turn. It makes the impossible possible...


Edit: Someone chimed in about the z28's rigidity and it makes total sense... The z28/ZL1/1LE and SS ALL have very similar torsional rigidity. There has been no major reinforcement added since 2011. It is in fact a shared structure and only minimal support was added.

They are blistering around Nurburgring in a $15,000 structure with $60,000 dollars worth of band-aids... and then some when you factor in the cage and additional tuning for the Ring car only.

Edit: Another chime says:

The z28's rear bias can increase nearly 7% with a traditional 8 point roll cage with cross bar (for harness mount). On an empty tank (enough to do a lap), the z28 goes to a 48/52 rear bias. It is a different car...

Go to know, I would need to ask for pics or figures from the shop to confirm but, it seems feasible.

With test equipment mounted in the trunk (conveniently over the rear axle), who knows...


I am will to dismiss the runs on balance alteration alone. Torsional Rigidity is just another major factor to dismiss these Comic book Hero runs and sell them as stock.

 

[thePill]

Eat some crow???

Read this...

Vorshlag just posted "We just weighed the lightest S550 Mustang GT ever at 3593 pounds. This is a non Premium, non performance pack V8 "

https://www.facebook.com/terry.fair?fref=ts

All stock with nothing removed? I am trying to confirm but, it looks like it may be so. Let's see where the fuel was at.

Be advised, this is still 23lbs heavier than a Non-Premium, Non-Performance Pack 2014 GT.

 

[DivineStrike]

Lol, I still haven't been able to find anything from vorshlag regarding his quote. Maybe they took it down. If it is with an empty tank that would put it at about 3692lbs

Don't start touting victory just yet

 

[02gtnh]

Boy people just jump to quick on a so so quote and act like its fact without knowing the whole story. He weighed his last GT empty and all the junk out from the trunk. So it would not surprise me if he did the same with this one.

 

[thePill]

Boy people just jump to quick on a so so quote and act like its fact without knowing the whole story. He weighed his last GT empty and all the junk out from the trunk. So it would not surprise me if he did the same with this one.

That was his GT that he picked up from the dealer. This GT was not his...

He weighed another customers z28 with A/C and 3/4 tank so, I'm not sure.

That junk weighs a total of 13lbs.

Appearently, these S550's have a 48/52 balance with a cage and very little fuel. That is good news.

It appears that their 2011 Brembo GT weighed 3563lbs completely empty. The GT gained a couple pounds since then.

All things aside, it is almost a wash.

2011 Brembo GT - 3563lbs

2015 GT - 3693lbs

The 2013 GT should have been between 3563lbs and 3593lbs the '15 was weighed. This is very, very good news. This is why Terry is excited. He sees a potential 3300lbs Comp GT to replace the white one.

 

[02gtnh]

That was his GT that he picked up from the dealer. This GT was not his...

He weighed another customers z28 with A/C and 3/4 tank so, I'm not sure.

That junk weighs a total of 13lbs.

Appearently, these S550's have a 48/52 balance with a cage and very little fuel. That is good news.

It appears that their 2011 Brembo GT weighed 3563lbs completely empty. The GT gained a couple pounds since then.

All things aside, it is almost a wash.

2011 Brembo GT - 3563lbs

2015 GT - 3693lbs

The 2013 GT should have been between 3563lbs and 3593lbs the '15 was weighed. This is very, very good news. This is why Terry is excited. He sees a potential 3300lbs Comp GT to replace the white one.

:shrug:

 

[thePill]

His 2011 Brembo GT with no fuel weighed 3563lbs. This 2015 GT weighed 3593lbs under the same circumstances yeah?

This is about as good as news as your going to get in the modern age when weight is concerned. Another bonus here is we get to compare a no option, base GT to their fully loaded, premium GTPP that weighed 3718lbs on empty without the 13lbs in the trunk.

Why is it good? Because it shows us the option gap from the Base to Fully Loaded Premium GT.

Now, that would mean that 3718lbs GT weighed 3731lbs with the garbage in it. Let's check our numbers with Car and Drivers Fully Loaded Premium GTPP on full at 3814lbs. A full 16 gallons of gasoline weighs 16 gallons X 6lbs per gallon is 96lbs. That would be 3827lbs... a 13lbs differance and, well within my 20-30lbs variance.

Now, remember we were asking ourselves how much option weight there was total? Using the 3593lbs and 3731lbs we get? 125lbs if removing the junk, 138lbs if not.

So, 3676-3685 is the lightest we can expect right now. That's about 30lbs from advertised and, about the same differance in the S197's (3580lbs vs. 3616lbs). Adding in the 96lbs for fuel brings us up to that number as well.

Since 125lbs of options exist, I would say 60-80lbs is Performance Package, 35-50lbs for a Premium 12 speaker and around 20-30lbs of stand alone options.

Also keep in mind, we have observed a 13lbs variation first hand. That could be +/-13lbs.

If there are 3675lbs GT's out there, I am betting we see some lighter than that but not by much. There could also be Base GT's that are close to 3700lbs too. A 20-30lbs variation would be 3655lbs - 3695lbs (20lbs for an Auto and we seen a Base GT auto weigh 3705lbs).

Everything I discussed seems very feasible. One thing is for sure, the 2015 GT was only 30lbs heavier than the 2011 Brembo GT they weighed.

This is very good, especially with the extent of the equipment and the addition of IRS.

 

[DivineStrike]

Pill, it's only ever been about 100lbs or so of extra equipment from base to fully loaded...I'm not sure what you're saying is good...maybe your just finally accepting the reality that unfortunately the 15 is still significantly heavier than the 14... Then again I haven't seen these numbers confirmed just yet, so let's just weight and see what happens with this quote ;)

 

[thePill]

Pill, it's only ever been about 100lbs or so of extra equipment from base to fully loaded...I'm not sure what you're saying is good...maybe your just finally accepting the reality that unfortunately the 15 is still significantly heavier than the 14... Then again I haven't seen these numbers confirmed just yet, so let's just weight and see what happens with this quote ;)

I would if there wasn't such a small gap between their Brembo '11 and the '15, both on empty.

I'm not really concerned with the packages and options. I can live with 30lbs especially with IRS.

One of my main points was, Base GT's are a little lighter than the advertised 3705lbs. I am still curious if it includes anything else.

As of now, the S550 looks to be nearly identical to a 2011 Brembo GT's race weight. The addition of a cage actually gives the S550 a rear weight bias. That bias could be as good as 46/54 and that is far superior than the S197.

They need to save about 350lbs to match the '13-'14 GT/Boss 302S full potential. It will be close, hopefully that can settle at 3200lbs with cage and spec equipment. Even losing race weight has become difficult.

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