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Put all three on mine first thing. Problem, venom brace, and backbone. Made a HUGE difference in handling.
 

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I put in the Werks rear frame brace, Werks front frame brace, Werks front shock tower brace and the DDM Probeam.

I added onto the the rear frame brace and also the probeam essentially making them a single unit.

I have not been sold on the backbone brace doing a whole hell of a lot. I would need to drive a Solstice with that being the only chassis/suspension modification to be able to tell. From an engineering standpoint it's not going to alter the torsional stresses on the vehicle between the front and rear an amount that would make it worth spending the money on. It's not long enough and it's attached to close to the center of the car.

I believe that the OE "brace" is not a brace at all. It is only there to stop the driveshaft from dropping should something happen to the rubber insulator in the shaft. FMVSS is what probably made them have that in there because of the driveshaft not having a metal on metal connection.

The only way to know for sure if it actually does anything is to attach string encoders diagonally across it from front to back and left to right . do that with the OE one and jack up on one of the front corners of the car by the control arm and record the readings. Then put the upgraded brace in and attach the encoders to the same spots and jack up the same corner the same distance and take the readings. If the upgraded one works the numbers would need to be lower. Whether or not it's worth the money is how much difference there is. I can see there maybe being a 1-2% change but not much more then that.
 

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When DDM introduced the BackBone they did a demo of the increase in chassis stiffness that it provided. They lifted one corner of the car with and without it and measured the amount that it had on an adjacent corner. The reduction in chassis twist is both obvious and substantial. There is also a distinct change to the feel of the car, with the BackBone making everything feel more solid.
 
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While I will always applaud making some effort over no effort, the DDM test is/was not indicative of any real world scenario nor did it follow any standard expectations for a chassis torsion test.

I believe the test you are referring to is summarized here: DDMworks Backbone Brace - Official announcement
Unfortunately, the pictures seem lost to time, which is sad because I'd love to plug their numbers into my torsion test spreadsheet.

The issues I have with this test are as follows:
1.) For the most part, vertical loads going into the chassis are not transmitted through suspension pickups. They are transmitted through shock mounts. For practical purposes, I could overlook this oversight, but it's not the only issue, and far from the biggest.
2.) They put too much load into the chassis to create their deflection. Lifting an entire side of the car? You'd be two-wheeling if you somehow managed to do that in real life. Over a severe bump or curb sure, but that's not really something you tune a chassis for. They needed to about half the load, based on my own experience and some shoot-from-the-hip estimation.
3.) They did not subtract the vertical displacement of the passenger side of the car. This may or may not be significant, depending on where they were measuring.
4.) This is the big one - the point they jacked from was not originally supported. If we assume that the chassis flexes relatively similar amounts in both positive and negative Z direction, all of their numbers are double what they should be. When they started measuring from "zero," that corner of the car was actually lower than the other 3. They had to lift it in order to get it back to the neutral height, and then they could start twisting the chassis. No-way-no-how should that displacement have been factored into their calculations.

Between all of this and my own experience, one has to assume that their calculated flex is - at a minimum - 4 times greater than it should be. It would not surprise me if it were even twice that.

All this is not to say that the brace doesn't improve torsional rigidity, but there's no possible way it improves it as much as the kappa world likes to think it does. KG's 1 or 2% is probably accurate based on my testing of a similar GM chassis, and that test involved going from a 1/4" aluminum piece up to a 3/8" multi-layed carbon/kevlar piece.
 

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While I will always applaud making some effort over no effort, the DDM test is/was not indicative of any real world scenario nor did it follow any standard expectations for a chassis torsion test.

.........

All this is not to say that the brace doesn't improve torsional rigidity, but there's no possible way it improves it as much as the kappa world likes to think it does. KG's 1 or 2% is probably accurate based on my testing of a similar GM chassis, and that test involved going from a 1/4" aluminum piece up to a 3/8" multi-layed carbon/kevlar piece.
I won't dispute a single thing you have said here, but will relate these four observations from putting a tunnel brace on my car:
  1. When driving diagonally over the gutter at the end of my driveway, one tire was lifted enough to be turned by hand.
  2. Driving through the subdivison the car felt substantially more solid.
  3. Driving on my favorite "test track" I found that the control was significantly degraded by asymmetric pavement, breaks, and small pothles.
  4. I took the brace off, and all three behaviors reverted to normal.
I am asolutely convinced that the brace increases stiffness, and am equally convinced that I do not like the result.
 
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I find it hard to believe that a piece of 3/8" thick aluminum adds sufficient strength counteract the rotation on the x axis at one end when the other end is being held in place with as large a cross sectional area as a vehicle has. You have to remember the mechanical advantage due to the axis being in the enter of the car and the forces are being applied one the outside edges of the vehicle.

If you took that backbone brace and attached one end of it to a fixed mount and then on the other end you attached a bar that is 1/2 the width of the vehicle how much force do you think you would need to apply to the end of the bar before the backbone brace started to twist.

I am going to tell you that it's not much. the difference between the stock stamped piece and the solid aluminum one is negligible because of the mechanical advantage. If you had a plate that went from the pinch weld to he pinch weld on the other side and it was bolted to the pinch welds... That would make a difference. because of how narrow the backbone brace is and where the attachment points in the vehicle are it's not a huge help.

Now.... If you boxed the transmission tunnel with 3/8" aluminum and attached either end of the box to the front and rear subframes by use of a cross member you would see a large change in the chassis rigidity.

I am not sure as to why it got named a "backbone" brace when the kappas do not have a backbone style of chassis so there is no backbone to brace in the fist place. The transmission tunnel is not any kind of a backbone. If you boxed the entire transmission tunnel and did the cross members at the subframes you would have then made the car a hybrid chassis where it has both the ladder and backbone styles.

For streetability flexing between the front and rear subframes is OK and is actually needed. The flexing is engineered to take place in very specific spots of the body. Even on a full frame vehicles this is true. Body mounts are the places that have been engineered to flex. Because unibody does not have body mounts key places in the body have been engineered so that they move without causing visible distortion of the painted areas.

As @JohnWR stated with the lifting of a tire off the ground because of a bump. Imagine hitting that bump going around a corner, think it would be better have all 4 tires planted on the ground or only 3 of them? I am pretty sure that 4 is going to be better.

In a race application that is not drag racing excessive twisting between the front and rear subframes is unwanted this is because of the difference in lateral forces between the front and the rear subframes when going around a corner. Ever ride on a roller coaster? Ever sat in the very last seat? You get the snot kicked out of you. the lateral forces in the rear are substantially greater then the front. In a car the same thing applies and if there is too much flex between the front and rear subframes the rear tire on the inside corner will lift of the ground. Back to the previous statement of 4 tires on the ground it better then 3 tires on the ground. It's a delicate balance based on application.

There is a point where stiff can be too stiff. This is when the vehicle is unable to handle variations in the road surface properly. The suspension plays an enormous role in chassis stiffening. Both things need to be approached at the same time. if you stiffen the chassis for a sock suspension and get it right for that suspension and then you put in a race suspension the chassis is going to be far too stiff.

The best thing to concentrate on when stiffening the chassis is what each subframe is doing. You want to keep those rails parallel and square to each other as that is going to effect the handling of the vehicle the most due to changes in in the alignment if the frame rails deviate from each other. Best things to do to help the chassis is to make a box between the shock/strut towers.

for the front of the Kappa something like this for the design would work
114955


and for the rear you apply the same principal

triangles = strength that's why they are used in the construction of bridges and tall buildings. Use them to keep portions of the frame square to each other. They take up minimal space and weight for the amount of strength they add.

Convertibles are going to have an inherently large amount of twisting between the front and rear subframes, this is because there is no roof structure that is apart of the chassis. If you stiffen up the chassis between the subframes by using frame connectors and or a roll cage handling performance of the vehicle will diminish when driven on the street. There needs to be some movement so places would need to be engineered into the deign to allow for movement if the vehicle is to be driven on the street.

I cannot even begin to tell you how much of an improvement there is from doing the boxing between the shock towers both front and rear. It's the difference between driving say a 1970's land yacht and a modern day super car.

Now if a tunnel brace was deigned from 4 pieces of 1/2" plate aluminum that formed a box approximatly 1" apart from each other and that was bolted down the full length of the tunnel so that either end could have a cross member attached to it that boletd to each subframe. That would make a large change in reducing the torsional twist. The key is attaching to the front and rear subframes and making a box and having walls inside the box. The "walls" would need to have different angles in different directions.
 

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Logically your 100% correct but my experience mirrored @JohnWR almost exactly. With just the pro beam installed the car felt a lot more planted and didn’t have anything close to the flex when I jacked it up. Roads i know quite well with a lot of bumps or defects would unsettle the car much more.

The impact to the cars ride was even noticed by my wife who didn’t know I installed it. She voluntarily comment that the ride felt firmer. I specifically remember the firmer comment as i followed up with a nsfw joke. 👋

I find it hard to believe that a piece of 3/8" thick aluminum adds sufficient strength counteract the rotation on the x axis at one end when the other end is being held in place with as large a cross sectional area as a vehicle has. You have to remember the mechanical advantage due to the axis being in the enter of the car and the forces are being applied one the outside edges of the vehicle.

If you took that backbone brace and attached one end of it to a fixed mount and then on the other end you attached a bar that is 1/2 the width of the vehicle how much force do you think you would need to apply to the end of the bar before the backbone brace started to twist.

I am going to tell you that it's not much. the difference between the stock stamped piece and the solid aluminum one is negligible because of the mechanical advantage. If you had a plate that went from the pinch weld to he pinch weld on the other side and it was bolted to the pinch welds... That would make a difference. because of how narrow the backbone brace is and where the attachment points in the vehicle are it's not a huge help.

Now.... If you boxed the transmission tunnel with 3/8" aluminum and attached either end of the box to the front and rear subframes by use of a cross member you would see a large change in the chassis rigidity.

I am not sure as to why it got named a "backbone" brace when the kappas do not have a backbone style of chassis so there is no backbone to brace in the fist place. The transmission tunnel is not any kind of a backbone. If you boxed the entire transmission tunnel and did the cross members at the subframes you would have then made the car a hybrid chassis where it has both the ladder and backbone styles.

For streetability flexing between the front and rear subframes is OK and is actually needed. The flexing is engineered to take place in very specific spots of the body. Even on a full frame vehicles this is true. Body mounts are the places that have been engineered to flex. Because unibody does not have body mounts key places in the body have been engineered so that they move without causing visible distortion of the painted areas.

As @JohnWR stated with the lifting of a tire off the ground because of a bump. Imagine hitting that bump going around a corner, think it would be better have all 4 tires planted on the ground or only 3 of them? I am pretty sure that 4 is going to be better.

In a race application that is not drag racing excessive twisting between the front and rear subframes is unwanted this is because of the difference in lateral forces between the front and the rear subframes when going around a corner. Ever ride on a roller coaster? Ever sat in the very last seat? You get the snot kicked out of you. the lateral forces in the rear are substantially greater then the front. In a car the same thing applies and if there is too much flex between the front and rear subframes the rear tire on the inside corner will lift of the ground. Back to the previous statement of 4 tires on the ground it better then 3 tires on the ground. It's a delicate balance based on application.

There is a point where stiff can be too stiff. This is when the vehicle is unable to handle variations in the road surface properly. The suspension plays an enormous role in chassis stiffening. Both things need to be approached at the same time. if you stiffen the chassis for a sock suspension and get it right for that suspension and then you put in a race suspension the chassis is going to be far too stiff.

The best thing to concentrate on when stiffening the chassis is what each subframe is doing. You want to keep those rails parallel and square to each other as that is going to effect the handling of the vehicle the most due to changes in in the alignment if the frame rails deviate from each other. Best things to do to help the chassis is to make a box between the shock/strut towers.

for the front of the Kappa something like this for the design would work
View attachment 114955

and for the rear you apply the same principal

triangles = strength that's why they are used in the construction of bridges and tall buildings. Use them to keep portions of the frame square to each other. They take up minimal space and weight for the amount of strength they add.

Convertibles are going to have an inherently large amount of twisting between the front and rear subframes, this is because there is no roof structure that is apart of the chassis. If you stiffen up the chassis between the subframes by using frame connectors and or a roll cage handling performance of the vehicle will diminish when driven on the street. There needs to be some movement so places would need to be engineered into the deign to allow for movement if the vehicle is to be driven on the street.

I cannot even begin to tell you how much of an improvement there is from doing the boxing between the shock towers both front and rear. It's the difference between driving say a 1970's land yacht and a modern day super car.

Now if a tunnel brace was deigned from 4 pieces of 1/2" plate aluminum that formed a box approximatly 1" apart from each other and that was bolted down the full length of the tunnel so that either end could have a cross member attached to it that boletd to each subframe. That would make a large change in reducing the torsional twist. The key is attaching to the front and rear subframes and making a box and having walls inside the box. The "walls" would need to have different angles in different directions.
 

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It could be that there is such a large amount of twist between the front and rear subframes on the Kappa that the backbone brace would make a sizeable difference. I very much believe that is possible knowing how much movement there is in the rear low rear control arm mount when cornering. So much movement that is changes the camber to a positive and the toe to being out on the wheel that is on the outside of the corner.

The question then becomes if there is that much twisting occurring would a tunnel brace be sufficient in it's design to remove enough of that twist to make the car proper again. I don't know the answer to that. I am going to have to get some 1/2" plate aluminum and make a brace. Then put together a rack capable of measuring the weight at each corner of the car and lift up on one corner until the weight lessens on any of the other 3. measure the force used to lift. then put the frame brace in and repeat the test and see how much of a difference there is.

It wuld be nice to be able to say that a tunnel brace reduces torsional twist between the subframes by n%. This allows us to know how much of an improvement it is.
 

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Discussion Starter · #31 ·
Thanks for all your help. I found the problem, and it was actually one of the first things I should have checked. 🤦‍♂️🤦‍♂️🤦‍♂️

There were 2 different size tires on the rear!!!!
I had a stock size 245/45R-18 on the left side and a 245/35R-18 on the right. I replaced the tire with the correct size and all is well now.
 

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Thanks for all your help. I found the problem, and it was actually one of the first things I should have checked. 🤦‍♂️🤦‍♂️🤦‍♂️

There were 2 different size tires on the rear!!!!
I had a stock size 245/45R-18 on the left side and a 245/35R-18 on the right. I replaced the tire with the correct size and all is well now.
Don’t blame yourself for missing that one.
It is one of those things that are so basic and logical as an expectation of the previous owner..
Like gas goes in the gas hole and oil in the oil hole that I would have never thought to check that either.
Glad you caught it before it became expensive :)
 

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Glad you found it! And that it was that simple of a fix
 
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A normal working car shouldn't exhibit this trait. It's fundamental failure of a component. In the OP's case it was mismatched tire size (yikes!). Glad the fix is easy. For others with similar experience without mismatch tires, it's a real concern. Adding a mod or reinforcement hides the issue.
 

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Wow that previous owner was an idiot 🙄
An idiot or a jerk? Putting that tire on the car to drive it is one thing, but putting it on to sell it is quite another.
 
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Wouldn't the traction nannies go bananas with the difference in wheel diameters? I know some cars will have 2-3% tolerance. The OP's rear wheel diameters have a 7.2% difference. Maybe our Kappas are more liberal. :unsure:
 

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....... Adding a mod or reinforcement hides the issue.
I think that "hides" may not be appropriate, at least not for all situations.

For example: The rear suspension has a flex that occurs under high cornering loads, causng some instability in handling. It is not present at "normal" speeds, and is not dangerous in any case. Installing one of the rear suspension braces corrects the issue, it does not hide it.

Wouldn't the traction nannies go bananas with the difference in wheel diameters? I know some cars will have 2-3% tolerance. The OP's rear wheel diameters have a 7.2% difference. Maybe our Kappas are more liberal. :unsure:
He has a 2.4, and from an earlier post it appears to be an early one, which means no traction or stability control, only ABS. So no nannies to get upset.
 
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