Topic: Review: DDM Backbone EXTREME and ProBeam

[Sky 5]

Increasing the rigidity, yes that is a word, of the tunnel section was obviously something that the engineers wanted
that's why there is a tunnel brace to begin with.

According to the GM parts catalog that piece is apparently not intended to be a brace of any kind;
and is simply described as a driveshaft tunnel cover, meant to protect the underbody, nothing more.

[Sol Asylum]

According to the GM parts catalog that piece is apparently not intended to be a brace of any kind;
and is simply described as a driveshaft tunnel cover, meant to protect the underbody, nothing more.

As a mechanical designer I don't buy that "its only a cover" thing for a second.  If it was only a cover they would have used less bolts or for that matter screws or even no screws at all but just some friction clips like how our interior panels are installed.  Also its just the driveshaft/transmission under there and most cars don't have any kind of cover there at all.

Actually all of the sales brochures that I have, Solstice and Sky make reference to the "enclosed center tunnel, which provides staunch resistance to torsional forces" or "...enclosed driveshaft tunnel add rigidity for agile handling."

No, its not just a cover.

[Ben L]

Critter's right.  The path of least resistance on torsional forces is the traction patch -- those little oval shaped areas where the rubber, literally, meets the road.  They will give way long before anything on the car breaks.

As for the notion that the tunnel brace was intended only to protect the underbod, all due respect, no sale.  The cars have a very tiny center section, and needed something to tie the sides together.

Honestly folks, there is no good reason not to stiffen the chassis with a Backbone and Pro Beam.  Drive it as hard as you are able.  It will not hurt the car in any way.  

I have a Race Backbone and Pro Beam, and a very stiff BC Racing coilover suspension, carrying spring rates more than double ZOK rates.  Overall the setup is far stiffer and more rigid than most would consider comfortable.  I autocross mine hard every weekend, and the game there is to try to stay at the outer limit of traction all the time.  I also drive it on the street every day, in all kinds of conditions, including a 500 mile round trip up to Pittsburgh and back last week which included 2 harrowing hours in the mountains of PA in severe thunderstorms with standing water up the rockers and zero visibility.  I have encountered bumps and wrinkles at very high speed, and have the car sideways lots of times.  

In other words I pound the crap out of my Kappa, and it is up to the task; plenty strong and solid.  If I ask too much, in straight line, or tossing it into a turn, the tires break traction.  That is all.

Carrying the Pro Beam and Backbone decreases the unwanted chassis movement that makes for "noise" and unpredictability in what you feel in your seat and hands when you push the car to the limits.  And that's a good thing.

Finally, consider this.  The first thing they teach you in track school is that the average passenger car's limits are far, far beyond where 90% of average drivers, and 80% of would be race drivers, think they are.  At one of my first track schools at Summit Point, and instructor popped the hubcaps off of a basic Enterprise rental Dodge, and took it out on the Shenandoah Circuit, and with plain old street tires screaming, turned times that were better than most of the prepped cars in the "red" driver's group.  That was an eye opener.  Kappas are bred for performance, and their limits out of the box likely exceed the average rent a wreck.  In other words, you'd have to be the Stig to worry about breaking this car just from pushing it too hard, provided you don't lose it and hit something.


 

[Sky 5]

Never meant to imply that reinforcing that tunnel cover is a bad idea.    Have already done so and it obviously helps in handling. Was merely pointing out that the Kappa framerails and crossbeams were specifically designed to handle certain loads. Those two under body tin pieces covering the driveshaft and the transmission were likely meant to: A.)Protect those areas because the cars sit so low;  and B.)Direct the airflow under the car to reduce turbulence.

[Sol Asylum]

I respectfully disagree with you about what they were meant to do.  They are stamped sheet metal and not aluminum plate from the factory because steel=$10/part and aluminum=$70/part, and if a union employee has to sit and watch a CNC machine make the part its probably more like $200/part.

When DDM was testing for flex did they try and test the car without any cover installed?  I bet even the stamped steel part made a huge difference.  Most people see that stamped part flex pretty bad but that is in part because it is out of the car when they are flexing it, when its bolted in place its actually pretty rigid just not as much as the aluminum plate.

[Sky 5]

  As it is, the exact purpose of the tunnel cover may never be known.
. . . . . There are at least 4 good reasons for it to be there:

A.) Protect the driveshaft itself from any number of road hazards
B.) Insulate the tunnel from the heat of the exhaust that runs right down below it.
C.) Tie together the lower central infrastructure in some way.
D.) Reduce underbody aerodynamic drag.

[Sol Asylum]

As it is, the exact purpose of the tunnel cover may never be known.
. . . . . There are at least 4 good reasons for it to be there:

A.) Protect the driveshaft itself from any number of road hazards
B.) Insulate the tunnel from the heat of the exhaust that runs right down below it.
C.) Tie together the lower central infrastructure in some way.
D.) Reduce underbody aerodynamic drag.

I don't know what kind of road hazards could possibly make it past the front bumper, inter cooler, oil pan, front cross member, etc and then be tall enough to inter fear with the drive shaft.  I have several other cars that sit closer to the ground with exposed driveshafts that have never had any issue with road hazards and have never heard any such stories from others as well.  One of the cars is in fact over 50 years old so if it had happened I am sure someone would have made mention of it by now.

A piece of 20 gauge steel has no insulating value, if that was the purpose there would have been some other material on top of the cover such as fiberglass or a foam.

If aerodynamics was a factor and not strength the part would be flat and not flanged and beaded.  A smooth flat surface will have less air resistance then one that has all the bends that are on our covers.  If undercarriage aerodynamics was a concern the underside of our cars would be quite different.

This cover actually makes it harder to work on the transmission and driveshaft and increases the cost to manufacture the car.  Given that GM uses this to market the car as an increase to rigidity.  I feel pretty comfortable in saying that that is exactly why it is on our cars.

[Ben L]

   With Sol Asylum.  Its a brace.  Dead horse already.

[Sol Asylum]

  With Sol Asylum.  Its a brace.  Dead horse already.

Holy Cow!  Hey Lil Goat I finally saw a post by that Ben guy!

[lil goat]

Yea who the heck is that Ben guy, I witnessed someone in a stock NA with the crap stock tires and a backbone, push the car to well beyond would most would even attempt last weekend, the car hung in there, I know exactly how hard she was pushing it I was in front of here, with much better tires and suspension. It seems when people talk of cars you hear the engineers did this and that, yea they probably did but then the bean counters came in and said you can't have that or this and make do with this. This is NOT the best car GM could build, it is the best car they could build for the money.

[GXPinKC]

Here is what is going to happen.  The forces that were causing the car to flex will still be present however because the frame is now stiffer these forces will be transmitted to other areas of the car and if the forces are great enough a new weak point will be found maybe by failure.  The real question is where?  Could be the bolts that hold the backbone in place, the suspension bushings, shocks, springs, control arms....

Increasing the rigidity, yes that is a word, of the tunnel section was obviously something that the engineers wanted that's why there is a tunnel brace to begin with.  There are a lot of other areas of our cars that I would expect to fail under extreme loads before there is any structural failure of the frame.  Tires, shocks and bushings are obviously designed to give and move about, I would think that if an extreme load was applied to our cars that we would over stress these items first and you would most likely notice that part failing.

The problem is that only the engineers that designed our cars or someone else that has all the design information can accurately do a stress analysis and predict where this next weak point is.  But keep in mind our cars were designed to also have a safety factor in the structural strength and I doubt that changing the tunnel brace will exceed that.

Maybe I am wrong but most of the loading that results in body flex is from turning the car and if the body becomes so rigid that it will not flex that force will be transmitted throughout the car until it is exerted on the connection between the tires and the road.  My gut feeling is that this would be where one will see the failure and that would be the car loosing traction and skidding.  However if the tires have such great traction that it doesn't loose grip how long will the sidewall remain firm before it rolls off the bead of the wheel?  I guess what I am saying is that I think rubber items will give long before any of the metallic one.

Bringing this thread back for selfish reasons as well as the fact that we are now at June 4Th and soon to be headed to the Nationals in Denver.  I don't know about you but I am starting to get reved up about the meet.  One reason is that Carol and I will be able to get our 3/8Th's Powder coated Race Backbone and Pro Beam installed by Dave at DDMWorks.  I don't know about you, but I am stoked about the Denver National Meet.  I have quoted this post by Sol Asylum because I happen to agree with it in the hopes that additional comments may come to pass on this topic.

Can't wait to meet all you guys and gals at the Nationals.  It sould be an awesome Meet!  Has anyone else signed up for the installs from DDMWorks?

[lil goat]

I don't agree with SA at all, it is a cheap piece of crap because all the budget allowed for was a cheap piece of crap. The engineers rarely get what they want unless they work for BMW or Ferrari. The is an inexpensive roaster for the common man, don't try and make it into some engineering marvel. Look at the freakin interior, what self respecting designer would let that go out the door if there was money to do something better. Keeping costs down was a PRIORITY with this car, and supposedly GM lost money on them, sure looks that way doesn't it. Don't over think the engineering on our cars, think engineering on a budget. There is absolutely no way taking flex out of the car will cause more failures, most likely it will cause less. Take an old Coke can and bend it and flex it over and over, what happens it breaks. Our chassis is pressed steel, not a fan of constant torsional stress.

[Ben L]

   Basically what I been saying.  More chassis stiff good.

[Kelu]

I have my backbone removed for 2-3 days is definitely a difference between off and stock on, I get Low Traction more often even as stock car, f so I might conclude: a stiffer backbone for sure will mean better reaction of the car.

[Sol Asylum]

I don't agree with SA at all, it is a cheap piece of crap because all the budget allowed for was a cheap piece of crap. The engineers rarely get what they want unless they work for BMW or Ferrari. The is an inexpensive roaster for the common man, don't try and make it into some engineering marvel. Look at the freakin interior, what self respecting designer would let that go out the door if there was money to do something better. Keeping costs down was a PRIORITY with this car, and supposedly GM lost money on them, sure looks that way doesn't it. Don't over think the engineering on our cars, think engineering on a budget. There is absolutely no way taking flex out of the car will cause more failures, most likely it will cause less. Take an old Coke can and bend it and flex it over and over, what happens it breaks. Our chassis is pressed steel, not a fan of constant torsional stress.

I agree with LG (except for the part which would mean I disagree with myself, no I don't, yes I do, shut up... ).

What I was trying to say was replacing the stock brace for a stiffer one is not a bad thing and that our cars are not prone to some great disaster if we do change it out.  The forces that cause the twisting will still be present they just won't be bending the  car.  I have no idea what they will do, it would require more data and analysis, but my opinion was/is that at worst if enough forces are generated it would just cause the car to slide.

Go back and read my other posts in this thread and you will see that I also believe that we have the brace that we do because of economic reasons.

Kelu thanks for letting us know what it's like to drive without the brace.  You confirmed what I thought.  That without the brace, even the crappy OEM one, our cars are less rigid.

[GXPinKC]

I have my backbone removed for 2-3 days is definitely a difference between off and stock on, I get Low Traction more often even as stock car, f so I might conclude: a stiffer backbone for sure will mean better reaction of the car.

Ok, so what if you had the Pro Beam installed as well!  I am having the Race 3/8" Backbone and the Pro Beam installed by DDMWorks at the Denver National Meet on Thursday, and I can't wait to drive it afterwards.  We will be running the Peak to Peak with Aspen Rose on Friday and the Red Rocks on Saturday.  It will be fun to see if we notice a difference although at the lower speeds will probably be harder to measure.  I plan to find a secluded spot somewhere up there in Denver where a good test can be accomplished.  Since we are visiting my nephew and his family in Boulder at various times during the Meet and he and his family live just 9 miles from the Meet, I hope my nephew Greg will be able to tell me of a good spot to test "Miss Red Eagle" and I will drive and give him a chance to drive.  I don't know if Denver has a Track or Raceway or not?  That would be superb!  We have had her at high altitude before but not in Colorado.  What a great state to find out the difference.  Now, if my wife will let me install the Wester's Tune, I will be good to go!

[Dan]

I see my race backbone is finally "Out for Delivery".  Get here, UPS.  Please! 

[Kelu]

I just made my custom backbone and installed it, damn is heavy (over 22 pounds), is made out of a plate 3/8 inch thick (3.15/8 inch to be more accurate) and I felt the car with all system OFF (ESC + TC) as it was yesterday with all systems ON and without any backbone.

I have posted some pictures with mine over here: http://kappaperformance.com/forum/index.php?topic=1950.msg22862#msg22862

Definitely this is a must in terms of performance.

[Dan]

Thanks for the link, you have done some really nice work. 

[Treeman]

I see both sides of the additional stress argument.  Yes, this car was designed on a tight budget and they may not have stiffened it more because of resources.  But this is a cheap part.  Also, they may simply may have not thought of this more.  Folks don't think of everything.  They did design the central tunnel deliberately to be stiff.  But I also wonder about transferring flex stress to other parts or welds not designed with the additional load in mind.  Flash's Owner on the other forum might could speak to this - he was on the design team and I think it was chassis.  He'd know.  I'd ask him myself but I'm a newbie and they are nannying my posts until they are convinced I'm not a bot (THANKS for not doing that here!).  Actually, I don't think anyone is at the helm over there because after a week or more, nothing of mine is getting posted.  (Again, love it here!). 

I wonder if they stiffened up the 2009 GXP?  I've only had the car 2 months, so I'm in the grinnin' not pickin' stage, but it seems plenty stiff to me.  So much so that when I cross the crown of the road pulling out of my driveway, I have problem not getting unintentional wheel spin on the inside wheel even if I'm not in rocket mode.  I have just put that down to weight transfer with a short wheelbase and a stiff car.  Has anyone done this in a 2009?  Still see the big difference folks are raving about?

[lil goat]

One of the biggest things you notice with a stiffer backbone is going over RR tracks, the car doesn't shake and rattle. Next place you can see the flex is if you head into a sweeper turn, and you are sensitive to it you can feel the car flex as you apply power, then as you straighten out it will unflex, as it flexes it will actually transfer weight off the inside tire to the outside tire as the chassis is twisted. With the backbone car will drift out with both back tires planted very controllable, and fun.

[Treeman]

Cool!  I really notice your last point.  OK, another to-do.  Thanks!

[Dan]

I installed my race backbone yesterday.  Ride and handling is much improved.  It really is every bit as good as everyone says.  Amazing!  Thanks DDM.
 

[SolNut]

Put the Extreme in/on the Coupe today.  No finite impressions, but the rough stuff in the subdivision did seem to be better on the way out to the highway. 

I actually had the sensation that the A$$ of the car felt a bit higher while I was driving.     Wasn't able to do anything real special to test it. 

Might take some time too, just returned a week or so ago from a 3.5K mile drive in it that included the Colorado Rockies (after the Nationals). 

Steve