Topic: GM engineer questions backbone

[lil goat]

It would seem the resident GM engineer doesn't think the backbone works and has issued a challenge of sorts over on the BB. Here is what he posted. By the way 3.5 millimeters = 0.137795276 inches or 1/8 of an inch, and it was steel they used.

Is the DDM Backbone made from steel or Al?

Some things to consider:

-When does a vehicle encounter significant torsion loading?
-How does the tunnel section generate "stiffness"?
-Can you pick the change out of several blind swaps?

I am getting a lot of questions in Private Message system about the benefits of the DDM Backbone.

We did work with increasing the tunnel belly pan thickness during the Z0K development, and tried double thick steel plate, approx 3.5mm. The predicted change in torsional stiffness was predicted to be minimal, and was not detectable blind.

Tell someone what part is in the car, though, and they definitely "FEEL" it. It would be interesting to spend a day in a garage, have several people evaluate a controlled blind study (the study would be randomized, the conductor of the study would not be an evaluator, and would consist of 6 evaluations where the belly pan was removed and reinstalled). No cross discussion allowed, as consensus can truly ruin a blind ride. It would take the better part of a day, but would be very worthwhile.

During the development of a vehicle, we do not always have the luxury to do blind evaluations, but I love to do them when possible. Nothing resets your ability to evaluate a vehicle than a blind evaluation. Nothing can be so humbling, either.

We also did a series of blind evaluations when increasing the rear crossmember stiffness, during the development of the GXP Z0K. The results of stiffening the rear crossmember were so dramatic that we went through the trouble of producing a specific beam for use on the Z0K club racing models. Expert evaluators could consistently, 100% of the time, determine whether a stock or a "stiffened" rear crossmember was in the vehicle. Normal drivers, on one evaluation run, had 11 of 12 able to pick the differences between identical vehicles, WITHOUT cross discussion.

My conclusions from this development work are that it is critical to increase stiffness of the rear crossmember.

DO THIS FIRST before moving on to other structural improvements. There are beams, braces, etc., but the critical part is that the rear crossmember must increase the stiffness of the beam and must attach the structure to the CENTER OF THE BEAM itself. If you do not do so, as in attaching a gusset at the corner of the beam and the drop-down bushing bracket, you will have wasted your time.

I know this from experience, my first attempt at strengthening the rear suspension structure was exactly this scenario. It did lead on to understanding how the crossmember functions in the system.

From people using the example of a thin Coke can, remember that Al has a fatigue limit no matter the strain. Steel has a strain limit, under which the fatigue limit is basically infinity. Consider too that this small can, the thickness of two sheets of standard paper, holds at times in excess of 100 PSI. It is all about the proper constraint and optimization of how the material is stressed.


The tunnel belly pan, and the trans belly pan both operate primarily in SHEAR, not bending. It closes out the tunnel, and provides the fourth side of a mostly square "torque tube" that is connected to the rails. That is why the number of fasteners (a dozen by memory) are so important. Constraining the edges is critical. The technicians used to mess with me (in jest, of course), removing a bolt or two in the tunnel belly pan during evaluations and changes. I would come back after and evaluations, puzzled by the change in steering or ride shake, and they would admit they were messing with me and put the bolt or two back in. The center bolts seem to be the most critical. So is cutting into the trans belly pan, so do not mess with this pan as it seems to be critical in providing the proper structural tie in to the front parts of the side rails.

The car is very stiff in bending, there is a large diameter torque tube, two large rails, and good structural tie-in to the loading points. Also, the tower offset at front is so close to the very large rail that we determined (again, by analysis and later evaluation rides) that a front tower brace is basically a waste of mass.
__________________
I am a GM Engineer.

Second Post

   
In fact, regarding a blind ride, I will volunteer my personal time some weekend in August to run a blind ride for the DDM backbone, if someone wants to sponsor it.

We could run a couple of them, depending on the results of the first one, I would suggest a comparison of the thickest one to the stock panel.

If that is successful, we could run a second one on the thinnest backbone vs. the thickest one, or even vs. the middle one.

If it passes both rides, I would consider it very conclusive that there is a detectable effect. It would be fun for me, I always love interesting puzzles. LOL
__________________

[kennysabarese]

my post beat yours by a few minutes, but i'll delete mine since you pasted the full text in there

[lil goat]

I can only cut and paste so fast, and I sent Dave a PM too. I do not post under the same name on the BB anymore.

[Sky 5]

The DDM backbone is aluminum and the engineer is just pointing out that the tunnel cover plate has several functions... as debated in another thread here.

[lil goat]

The DDM backbone is aluminum and the engineer is just pointing out that the tunnel cover plate has several functions... as debated in another thread here.

It's aluminum really? I never would have known thanks for that update, and I don't see any other uses mentioned, it adds stiffness.
 He states he questions if it works or not and wants to test it pretty clearly, he does say that the Pro Beam most likely does the same thing as the Z0K differential brace and is needed. I would have gone with the Z0K diff brace but it is number 1 more expensive and 2 much harder to install.

[TecSolOnt]

 So my take is he is suggesting the money is wasted on the Backbone, what about the safety aspect is he raising a question there as well with the material issue (i.e.  aluminum vs steel) ?  What about the ProBeam does he also have an opinion on that?

[snaponbob]

 So my take is he is suggesting the money is wasted on the Backbone, what about the safety aspect is he raising a question there as well with the material issue (i.e.  aluminum vs steel) ?  What about the ProBeam does he also have an opinion on that?

Here was my response to him --

You have been VERY helpful in answering my PM's and I really do appreciated the information. Two observations;
1) With spring rates now in the 400's, I really DO notice the increase in cowl shake. Not at all surprised and I am not complaining at all. It is not class legal for me to install the BackBone or I would. Reading what you said about all the bolts makes sense which answers a question I had about all of them.
2) Dave sent me a BackBone to evaluate KNOWING that I would/could not install the three big bolts in the cross member. The three bolts are the "make it or break it" for legality in SCCA Solo Street Prepared and SSM classes. I am here to say that I left the driveway, started hammering the car around, it DID help, and not by a small amount. (If it was legal to install the bolts I would do so as that would undoubtedly help even more.) The results were confirmed by removing it, driving it again, and then reinstalling it. It was a TOO significant change to be psychological!!! After installing poly bushing in the suspension the difference on vs off was even more noticeable. In "normal" driving there is no difference, but when driven in a "spirited" manner (ya' like that one?) HOW the rear end steps, HOW it acts after it steps out, and HOW it catches the slide it MUCH different - more predictable, more consistent, and more controllable.

[lil goat]

Did you mean Dave sent you a Pro Beam to evaluate Bob? No added bolts in a backbone.

 He has not come out a said the money was wasted, he said that when they installed a 1/8" thick belly plate made from steel, most likely pressed steel, they could not tell a difference. He says that a the Z0K differential brace made a very noticeable difference, it does the same thing as the Pro Beam, but requires that you drop the differential to install it and costs twice as much. He however has not tested the Pro Beam, if I am reading Bo right he has tested it and even without the bolts it makes a noticeable difference, should be even greater with the bolts in place. I had the backbone for several months before getting the Pro Beam and could easily feel the difference.

I would question whether the test car GM used with the thicker belly plate already had the Z0K differential brace, as this would have a big effect on the test.

[GXPinKC]

I am hopeful that a second GM Engineer steps forward with views on the subject.  I would like some further validation before taking further action.
At first I had some misgivings about it being aluminum instead of steel but I held my tongue.  I look forward to further comment on the issues this thread presents?  

[TecSolOnt]

  Very interesting discussion,   the computer simulation/engineering world suggests one outcome from a modified  backbone  the "experience" another. I have a lot of  respect for engineers and what they do but also realize that if it was that easy there would be little need for reality checks and real world performance. Then  there is the "placebo" affect which only blind studies can control for. I think this question will continue without an answer here...

  I am more interested in hearing his take on the safety aspect, there is a definite difference in how aluminum vs. steel acts in the real world where multiple types of  stresses are applied over time.

[snaponbob]

I am hopeful that a second GM Engineer steps forward with views on the subject.  I would like some further validation before taking further action.
At first I had some misgivings about it being aluminum instead of steel but I held my tongue.  I look forward to further comment on the issues this thread presents?  

For those that don't know who the above mention GM engineer is, he was involved on the Kappa project starting in 2002 and was heavily involved in the suspension development from the very start of the project, I met him in June 2006 at the 1st Sol Convention in KC.

[lil goat]

I am hopeful that a second GM Engineer steps forward with views on the subject.  I would like some further validation before taking further action.
At first I had some misgivings about it being aluminum instead of steel but I held my tongue.  I look forward to further comment on the issues this thread presents?  

My advice install it and test for yourself. You will never get "the proof" you seem to want. It just really isn't nearly as complicated as you want to make it, it is just a flat plate. It is not going to cure cancer, and how many people do you need to say it works for you to believe. I do not know of even one person that has installed it and said "hey this doesn't work" and put the old one back. We are not all full of crap.

ALL convertibles are less stiff than hardtops, the roof adds a lot of stiffness, the Solstice has a particularly short frame so improving stiffness really helps, it maybe that steel would be a better choice but Kelu made one and it weighed 28 lb's  instead of 9 that is a lot of added weight. I drive my car VERY hard and would not give the backbone back for anything, if you don't push your car you will see little benefit other than improved stability crossing RR tracks.

I have worked with engineers for my entire career, this GM engineer seems to be grounded in the real world better than most. He has offered to test the product blind, that is when the answers will come. I have done my testing as have many others, the results are not just in my head. I have bought plenty of junk in my day, and have been the first to admit it when I wasted my money.

[snaponbob]

Did you mean Dave sent you a Pro Beam to evaluate Bob? No added bolts in a backbone.

 He has not come out a said the money was wasted, he said that when they installed a 1/8" thick belly plate made from steel, most likely pressed steel, they could not tell a difference. He says that a the Z0K differential brace made a very noticeable difference, it does the same thing as the Pro Beam, but requires that you drop the differential to install it and costs twice as much. He however has not tested the Pro Beam, if I am reading Bo right he has tested it and even without the bolts it makes a noticeable difference, should be even greater with the bolts in place. I had the backbone for several months before getting the Pro Beam and could easily feel the difference.

I would question whether the test car GM used with the thicker belly plate already had the Z0K differential brace, as this would have a big effect on the test.

1) I have the ProBeam installed to comply with the SCCA Solo rule - i.e. without the three center bolts. CLEARLY much better than stock.
2) I did the ProBeam BECAUSE I didn't want to spend the money or time to install the Pontiac GXP/Z0K rear frame piece.
3) Some time ago I received an e-mail that said GM had played with the ProBeam and it worked as well as the Pontiac piece !!!

[smartin]

If it's Steve, then I know him, too. And I respect his opinion very much. With that said, I still know what I can tell from the installation and I made a post on the BB stating as much.

[lil goat]

I will tell you no one ever tested a backbone on an NA harder than Smartin did, I was there. If she says it works believe her even if you don't believe me

[smartin]

Thanks goat

[GXPinKC]

It would seem the resident GM engineer doesn't think the backbone works and has issued a challenge of sorts over on the BB. Here is what he posted. By the way 3.5 millimeters = 0.137795276 inches or 1/8 of an inch, and it was steel they used.

Is the DDM Backbone made from steel or Al?

Some things to consider:

-When does a vehicle encounter significant torsion loading?
-How does the tunnel section generate "stiffness"?
-Can you pick the change out of several blind swaps?

I am getting a lot of questions in Private Message system about the benefits of the DDM Backbone.

We did work with increasing the tunnel belly pan thickness during the Z0K development, and tried double thick steel plate, approx 3.5mm. The predicted change in torsional stiffness was predicted to be minimal, and was not detectable blind.

Tell someone what part is in the car, though, and they definitely "FEEL" it. It would be interesting to spend a day in a garage, have several people evaluate a controlled blind study (the study would be randomized, the conductor of the study would not be an evaluator, and would consist of 6 evaluations where the belly pan was removed and reinstalled). No cross discussion allowed, as consensus can truly ruin a blind ride. It would take the better part of a day, but would be very worthwhile.

During the development of a vehicle, we do not always have the luxury to do blind evaluations, but I love to do them when possible. Nothing resets your ability to evaluate a vehicle than a blind evaluation. Nothing can be so humbling, either.

We also did a series of blind evaluations when increasing the rear crossmember stiffness, during the development of the GXP Z0K. The results of stiffening the rear crossmember were so dramatic that we went through the trouble of producing a specific beam for use on the Z0K club racing models. Expert evaluators could consistently, 100% of the time, determine whether a stock or a "stiffened" rear crossmember was in the vehicle. Normal drivers, on one evaluation run, had 11 of 12 able to pick the differences between identical vehicles, WITHOUT cross discussion.

My conclusions from this development work are that it is critical to increase stiffness of the rear crossmember.

DO THIS FIRST before moving on to other structural improvements. There are beams, braces, etc., but the critical part is that the rear crossmember must increase the stiffness of the beam and must attach the structure to the CENTER OF THE BEAM itself. If you do not do so, as in attaching a gusset at the corner of the beam and the drop-down bushing bracket, you will have wasted your time.

I know this from experience, my first attempt at strengthening the rear suspension structure was exactly this scenario. It did lead on to understanding how the crossmember functions in the system.

From people using the example of a thin Coke can, remember that Al has a fatigue limit no matter the strain. Steel has a strain limit, under which the fatigue limit is basically infinity. Consider too that this small can, the thickness of two sheets of standard paper, holds at times in excess of 100 PSI. It is all about the proper constraint and optimization of how the material is stressed.


The tunnel belly pan, and the trans belly pan both operate primarily in SHEAR, not bending. It closes out the tunnel, and provides the fourth side of a mostly square "torque tube" that is connected to the rails. That is why the number of fasteners (a dozen by memory) are so important. Constraining the edges is critical. The technicians used to mess with me (in jest, of course), removing a bolt or two in the tunnel belly pan during evaluations and changes. I would come back after and evaluations, puzzled by the change in steering or ride shake, and they would admit they were messing with me and put the bolt or two back in. The center bolts seem to be the most critical. So is cutting into the trans belly pan, so do not mess with this pan as it seems to be critical in providing the proper structural tie in to the front parts of the side rails.

The car is very stiff in bending, there is a large diameter torque tube, two large rails, and good structural tie-in to the loading points. Also, the tower offset at front is so close to the very large rail that we determined (again, by analysis and later evaluation rides) that a front tower brace is basically a waste of mass.
__________________
I am a GM Engineer.

Second Post

   
In fact, regarding a blind ride, I will volunteer my personal time some weekend in August to run a blind ride for the DDM backbone, if someone wants to sponsor it.

We could run a couple of them, depending on the results of the first one, I would suggest a comparison of the thickest one to the stock panel.

If that is successful, we could run a second one on the thinnest backbone vs. the thickest one, or even vs. the middle one.

If it passes both rides, I would consider it very conclusive that there is a detectable effect. It would be fun for me, I always love interesting puzzles. LOL
__________________

I met you and talked to you at the First National Solstice Meet In Kansas City, Missouri and enjoyed your speech later in the Meet from the Podium.  I do appreciate your comments with reference to this topic on this and other forums.  I do look forward to your blind ride some time in August, but somehow wish it could be done prior to the Denver Meet for those of us wishing to have it installed at that time.  Thanks Sir for your comments on this topic.

It was an extreme pleasure meeting you at the Meet.  Thanks for your information and expertise.

GXPinKC
Ron

[jonymac]

Just to add to the pile - as Goat pointed out, the keys here seem to be:

1. GM tested with 1/8 inch steel and not 3/8 or greater aluminum
2. We don't know if the car already had the Z0K bar

I installed the 3/8 race backbone and the before and after was OBVIOUS - not only to me, but to a passenger who didn't know I did the swap (and who isn't the remotest interested in my mod madness).  I say this even though I sheared two of my bolt heads off doing the install!  The way the car held together over bumps and through curves was night and day.  Again spirited driving or even going over railroad tracks felt different.

I then installed the probeam and felt what I would gauge was 25% more change in the handling - not as much as I had been expecting, but chalked it up to the fact that I already did the backbone.

I will concede that as humans, there probably is SOME placebo effect involved - but that can't be removed - it comes with committing resources and energy to a project.  However, there is absolutely no doubt in my mind that the backbone has changed the nature of the handling of my car.  I am now more motivated to tap out those two bolts I hosed!

BTW- I would love to participate in the blind ride project if possible!

JonyMac

[lil goat]

I met you and talked to you at the First National Solstice Meet In Kansas City, Missouri and enjoyed your speech later in the Meet from the Podium.  I do appreciate your comments with reference to this topic on this and other forums.  I do look forward to your blind ride some time in August, but somehow wish it could be done prior to the Denver Meet for those of us wishing to have it installed at that time.  Thanks Sir for your comments on this topic.

It was an extreme pleasure meeting you at the Meet.  Thanks for your information and expertise.

GXPinKC
Ron

Ron the GM engineer is not on this forum, he will not see your comments unless you post over on the BB, the thread is simply called backbone over there.

[GXPinKC]

Thanks goat.

[rich71]

jacking up a corner of the car without a cover, with the stock cover and then with the ddm, measuring the difference, like ddm stated, doesn't that prove it makes a difference? Maybe someone else can independantly verify the difference in flex? For the sake of arguement, if it doesn't make a "perceptional difference" in performance, less flex, helps with shakes and rattles of panels down the road, so even for that purpose, it doesn't hurt to install one. I beleive it performs as stated.

[Critterman]

Believers/non-believers,  leaders/followers,  engineers/drive by the seat of your pants people.


I tend to be among those who test products before others, no engineering experience.  So take my comments any way you want.

"IT WORKS!"

[Dan]

Couldn't be any more interesting timing for this one--I've had my race bone only since Monday.  I perceive a huge difference after adding it.

[TecSolOnt]

 Anyone looking for further info on the backbone issue from the Solstice Forum here is the link, some good back and forth on this. Beauty is in the eye of the beholder. Since I am going down to DDM in a few weeks for my STII and had planned on the backbone being thrown in now I may also add the ProBeam while I am there based on the feedback from the very knowledgeable engineer.

http://www.solsticeforum.com/forum/f101/backbone-54858/index4.html

[Ben L]

Whatever.  Enough talk. 

I know the difference I felt before and after.  Is everyone who has so commented just plain uninformed, wrong or hallucinating?

If you want the coke can thick stock bellypan, cool.  Enjoy every bit of that torsional rigidity and wonderful sheer resistance the stock set up delivers.

Have fun debating, too.  And believing everything served up over there on the ever-growing, always authoritative, Big Board

Meanwhile, I will just keep driving the snot out of my car.  With Race Backbone and three bolted Pro Beam.  Even in SCCA Solo events.  No matter what class they stick me in.

And . . . .  Loving it!