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If you really want to give the rear suspension a bump in how well it performs you might consider doing what I did. It made a HUGE difference in how the car handles.

If you jack up the back end of the car and let the suspension hang then snap a photo if the Werks frame brace from the rear of the vehicle, so you are looking at the back most bar from it's edge. The lower the car back down putting the weight back on the suspension then take another photo. compare the 2 photos. You will see that the bar is bending. This is deflection because the flat bad has no real rigidity to it along it's wide side. You can also test by taking the brace out of the vehicle placing 3 blocks on the ground at 3 of the corners have a person stand on the corner opposite the one that has no block and then step on the corner that has no block. It drops right to the ground.

what I did was I picked up some 1" x 1" x 1/8" steel angle iron and bolted to to the frame brace every 3" or so around the outside perimeter. Now when the previous test is done the 2 people can stand on it and the corner without the block doesn't even move.

I also bolted the Pro Beam and the Werks frame brace together at the control arm mounts using a piece of 1/4" plate steel.

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the reason why the 2 pieces i added on either side look crooked is because the pro beam is bent upwards because it matches the curve of the factory cross member.
the tops of those brackets are bent at 90 degrees and the 2 bolts on either side that bolt the side brackets that cam with the pro beam to the pro beam also bolt the ones I made. so there are a total of 6 bolts holding those side brackets in place.

The purpose to adding these is it keeps the rear mounts for the rear control arm square to each other.

sorry for the crude drawings but it will help to visualize the problem and why those brackets and L channel make a huge improvement.

So this is what the mounting system looks like for the lower control arms as seen from the back of the vehicle.
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this is the right rear control arm from a birds eye view

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This is what happens when taking a left turn. there are massive lateral forces being applied to that lower control arm on the right side. and this is what happens

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while both the Pro beam and the frame brace do help they do not have enough meat and potatoes to them to stop this from happening. they will make the amount of the movement smaller. The frame brace is going to deflect in the middle between the 2 rear lower control arm mounts and the pro beam simply sits to high up to stop it.


This kind if a design failure causes a very dangerous alignment change to the back of the car when taking a hard corner. you end up with + camber so the top of the tire will be out more then the bottom, and because the front mount on the control rm doesn't move and the back one does it toes the tire out. This will make the back of the car unbelievable loose and want to slide.


If you jack up the car and let the suspension hang. loosen the 4 bolts that hold the frame brace in place, back them out almost all the way, then lower the car back down you are going to see a gap form between the the frame brace mount and the lower control arm mount. and the gap isn't small either. between 1/8" and 1/4" on either side.

This is happening from only the weight of the car and no lateral forces involved!!!!

So when you drive the car and if you want the back of the car tighter keep this in mind.
 
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Discussion Starter #22
Good stuff there, I also wondered if the Werks piece should really have been square tubing, as I read their very first version may have been. I can drill holes and I also know someone with a welder, and know I have it installed I can really understand what kind of clearances I have. I'm defintely going to add some beef to that piece. This was my #1 concern for the suspension on the car when I started learning about it.
@kgschlosser What shocks are you running? I assume you autocross (roadrace?). What's your tire setup?
 

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I do not race, I have the stock shocks as they are Bilsteins and aren't bad to begin with and for sneakers I am running Firestone Firehawk Indy 500's I do not remember the exact size off hand, I know they are wider and have a slightly smaller sidewall then the stock tires. I will say that these things grip exceedingly well, damned close to the Yokohama Advan A048 (Lotus compound). Tires only last 10k-12k miles but that is to be expected because of the soft compound. They aren't horribly expensive, I paid <650 for a set of 4 mounted, balanced, disposal fee, changing all of the seals in the TPM sensors and taxes. The tires work fantastic on wet roads as well. snow on the other hand..do a whole lot of go no where really fast.. they have a stiff sidewall so I run them at 26PSI or so for some comfort. If I was to use them for autocross I would bring the pressure up to 30 or so, and I will say that they can be used in autocross no problem.

I know it is hard to find the right tire for a car, I will say that this tire is a really good match for the car's weight handling characteristics, suspension spring rate.. I have to replace mine in the spring and I will definitely be getting the same tire perhaps wider if I don't end up with to much cupping..

Where are you located? I can ship you the old set when I get them changed, they will be at or close to the wear bars so still have some usable tread on them.

it originally was square stock, it is shown on their website as square stock, I asked about it and was told that there wasn't any difference between the flat and the square in term of performance. I said bullshit, that's impossible. I can bend that flat bar by hand, and there is no way that I would be putting as much force on it then what the car is going to do to it. I had my buddy follow me with the brace in the car before I modified it. I left the rear valance and exhaust off the car. only a trip around the block. he said he could see the thing bending when I was taking corners and when I went over bumps. Even using the L channel it still bends a little. I can see it when I take the weight off the suspension. I have really been considering changing from the 1x1x1/8 to 1x1x1/4.. Can't really make the return on the L to much bigger then an inch because of the exhaust and If I notched it so the exhaust wouldn't hit it defeats the purpose of having the larger return and is also going to push all of the energy into a single spot making it bend much easier.

Welding it would also be better then bolting it, tho the bolts do add an aesthetic appeal to it.

Bending that 1/4" plate to make the 90 was fun.... I took a 6x6 piece of lumber and cut a 90 degree V out of the middle of it. used 3 high output propane torches to get the metal cherried. I set the metal in the block and used my shop press to push it into the V. Heated it up again and set it in the block, then use a 5lb hand sledge and a masonry chisel to bend it in the rest of the way and give the inside a nice clean 90 with no curve. I let the metal cool down in it's own time as I didn't want to temper it and make it brittle.
 

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Discussion Starter #25
After taking a look, my plan is: Weld 3/4 inch square tube along the back brace, along with some corner braces that are parallel to the ground, about 4 inches, just to cover the width of the suspension pickup. In an ideal world, the exhaust wouldn't be in the way and I could put diagonal braces from the pickup point up to the upper rear member, but in this case I can go to the DDM bar with a nice diagonal bar, and on the driver side, a diagonal bar but of course can't go to the right spot either at the top or bottom. I feel the diagonal brace like this will eliminate a lot of the flex, as we've all heard triangles make for rigid stuctures. I'm not sure how I feel about needing to reinforce the horizontal diagonals built into the Werks unit. There could be some value in that, but I don't have finite element analysis to calculate the stresses. It seems that they are needed for sure, but the load they carry is probably a lot lower than the rearmost crossbar. It's always something I could add later.

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There is no need for that much strengthening, but if you want to do it, go for it. Keep in mind that if you go with a muffler-less Solo exhaust later in life it's not going to fit.

For reference, when GM developed the track-spec Z0K package, all they did was add a doubler plate to the rear cross-member, and that solved the rear suspension issues. And those cars were running slicks and generating far more lateral force than something on street tires ever will. There is plenty of other documentation/development on this topic from a decade ago if you search it here or on the Sky forums, but the general consensus is always Z0K Beam=Pro Beam >> Werks Brace/ReBar.

I have not tested this myself, but I suspect you could probably remove the bolt on "fingers" of the pro-beam that drop down and there would be a negligible change in compliance.
 
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Discussion Starter #27
I'll be honest I'm new to the platform so I can't say I know everything. But I do feel that the GM z0k rear brace was probably the best most-minimal solution to rear flex, not the best 110% solution. The z0k was to be raced in SCCA in a showroom/stock class right? So in order to meet rules, it was probably within the rules and "light touch". Me, new to the car, took a look at those unreinforced mount points and said "nope nope nope". The Werks bar and DDM bar is IMO required (for what I want to get out of the car). And the SCCA cars were (probably?) on stock size tires, maybe even Hoosiers, but a car with 315 Hoosiers or even today's "200TW" can probably pull more G's (if maybe shorter time in-corner than a road course).
I appreciate the conversation! Thanks, I'm here to learn and share. :)
 

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the fingers on the Pro beam are what help to keep the towers square to the stock cross member. I'll say that they don't do a hell of a lot in that department but it does add something.

The square stock can be added going across this will 100% make a difference. The diagonals you can do if you do not want to make the plates for the sides like I have. those plats do the same thing the cross bars would do, they are simply smaller. If you make a square out of wood how to keep it from going out of square? add triangles to the corners just like you said.

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If you do with square stock and use 1" x 1" x 1/8" you would not need to do anything additional to the cross bar. if you use metal thinner then 1/8" then I would add a bar that goes straight up right dead smack in the middle to stop the middle of the frame brace from deflecting.

It is amazing how a center support like that will change the load capacity. If you have a 2.5" x 1/4" pipe that is 20 feet long it's end to end load rating is something along the lines of 20,000lbs, If you stop the center from deflecting the load rating goes up to 60,000lbs. and it doesn't take much to stop the center from deflecting a piece of 1" x 1/4" flat bar is all that would be needed.


Look closely at the photo above. then look at the next one.

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do you see it now??? this is with only the weight of the car. no lateral forces involved.. can you see the bow happening in that piece of 1" x 1" x 1/8" angle iron?

Even after adding everything I have added the damned thing is still bending. that tells me when the car is in some heavy cornering the towers are still moving some. Granted no where even close to what they were but they are still moving. This is visual proof of how much of bad design the back end of the car was. It all attributes some of the body panel alignment problems the Solstice and sky have.
 

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and if you want to do the brackets like I have you need to flip the brackets on the pro beam from left side to right side.
 

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I believe the SCCA road race (SSB, T2) guys had to run R-comp Hoosiers in stock 245 width.

The SCCA autocross guys ran 295 A-Comp Hoosiers, which was legal at the time in stock classes, and certainly generated the highest lateral loads, even if short duration.

If the LCA mounts moving was actually an issue tying them together with the Werks brace would be the worst and least efficient way to solve the issue. Not only does it not triangulate or brace anything back into the chassis, but it would subject the points on the unloaded side of the car to nearly equal and opposite movement as the loaded side was undergoing. This is probably why Werks did not notice much performance by getting rid of the box tube. They could have gotten rid of the entire thing and not lost much performance lol.

Note I'm not saying the mounts don't move. Of course they do. But history shows that the entire frame back there is moving more than the individual mounts, and that you'd end up with a better handling car by minimizing weight than you will chasing an infinitely stiff structure.
 

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If I correctly recall the discussions from 13 years ago, the Z0K brace was prohibited from being attached to anything other than the suspension pick-ups. The argument for its benefit was that tieing the two lower pick-ups together effectively doubled the stiffness of the loaded side, and that the reduction in movement of the loaded side outweighed any increase in movement on the unloaded side.

The DDM ProBeam added a bolt in the center than ties the whole thing into the cross-brace to further reduce movement.

When I installed mine I did not have the car high enough to drill the hole for the center bolt with the drill I had available, so i initially installed it without that bolt. Even on the street and on street tires I noticed a significant benefit to the brace. Adding the bolt provided an additional benefit, but the second improvement wasn't as great as the initial one.
 

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Keeping the LCA mounts square to each other (side to side) is incredibly important and the issue is no so much that things are moving back there as is how they are moving and what is being caused by the movement. The objective is to minimize/stop the movement of the rear LCA mount. So by attaching the 2 LCA mounts for together with something strong enough the load that is causing the one to bend is now going to be shared between the 2 mounts. The mount on the outside of the turn is seeing far greater load then the one one the inside. So moving that load can be done. Now once that has been done with the bat between the 2 mounts the mounts are going to move in unison. So they will come out of square relative to the frame rails. Like this.

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So how do you stop that from happening?? Add triangles to the corners. Exactly like what I have done.

I can tell you that a piece of 1"x1/8" flat bar is and does deflect because of the lateral forces. You are talking about 1,000's of lbs of force that is end to end on that skinny piece of flat bar.

If I took that flat bar and stood it on it's end and lowered 4,000 lbs onto it would you want to be under that weight?? I am going to guess the answer would be No. So now I ask why not? Because is is not going to support the weight without bending. Look at steel shelving units. How come they aren't made from flat bar? Because it is next to no end to end load carrying capacity because of deflection. The forces being applied are lateral and because the flat bar is horizontal the forces being applied to it are end to end.

A piece of 1"x1/8" steel flat bar with a span of 3 feet is going to start to bend with only a few lbs applied to the center of it. It's not going to take much more then a few hundred lbs end to end before it starts deflect. When it deflects then the LCA mount is moving.

I am no going to bother arguing this any further. I can see the problem. I believe that @ConeHugger01 can also see the issue. Even if I went and attached all kinds of string encoders and captured data showing the movement and then did the same with the modifications in place and showed the reduction you would still argue it. Even with photographic proof you are staying that the program and the brace solves the issue and doesn't need to be modified at all.

IDK what Weeks originally used for the box steel. If they used 1/2" x 1/2" x 1/16" then I can see where changing to the flat bar would make no difference. But changing from 1"x1"x1/4" down to the flat bar.. there is going to be one hell of a change.
 

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The pro beams design reinforces the corners of the towers to the cross member. Essentially adding 2 triangles to help keep the towers parallel to each other. Without the bolt in the middle the probeam doesn't touch the cross member. There is a gap. Well this gap allows the probeam to deflect thus reducing it's effectiveness. By adding the center bolt the deflection stops and provides a higher amount of support.

The probeam is designed for street applications. It is not designed to handle the types of loads that are going to be seen in autocross.

@JohnWR

You did notice a difference when stopping the deflection.. is it likely that stopping the deflection. On the Frame brace is also going to be a noticable change?? If so do you think it would be worth doing at the cost of 20 bucks and an hour's time? With is if competing??
 

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.........
You did notice a difference when stopping the deflection.. is it likely that stopping the deflection. On the Frame brace is also going to be a noticable change?? If so do you think it would be worth doing at the cost of 20 bucks and an hour's time? With is if competing??
If I was competing and the modification was legal for my class, I would probably try it, then compare lap times with and without it. If lap times didn't improve I would remove it because as @phil1734 suggested, any extra weight is too much.

For a street car I won't try it because the stock ProBeam remves all of the instability that I can detect, and I think that if it did anything it would have the same effect as the BackBone. ie: Make the car feel faster but cause me to drive it slower
 

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According to my model the rear lower suspension mount sees about 600lbs reacted through it, not 4,000.

This assumes a 3,300lb Solstice GXP doing a steady-state .9gs, and that the lower control arm carries 80% of the cornering force.

If I use my car at 3,100 lbs and 1.0g, it's 675lbs.

4,000lbs at that mount equates to 3.2gs.
 

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@phil1734 : I think your model under-states the load on the lower pick-up, as I claculate it to be closer to 1600 lbf at 0.9g. Of course that is still significantly less than 4,000 lbf.
 

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Discussion Starter #37
2021.02.14: I had to get at the battery to disconnect it and it was a huge pain so I had to reorient it for easier access.

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I really really wanted to get the engine running. I had my 2nd radiator come in from Werks, and it has the same 1-1/4 inch ports as the RPM Motorsports rad. So I kept the RPM one since I had handled it a bunch already. I used self fusing silicone tape to bulk up the ports to a fatter size, and used screw down hose clamps.

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I have a vacuum draw tool to fill it. But then I saw the coolant line to the turbo had some kinks in it. I had this hose off for weeks but did not think it needed replaced, until reading the manual about not bending them too much or the plastic inside gets kinked. So another RockAuto order and I'm waiting. It looks like an easy replacement once the exhaust and cat are off, which is pretty easy.

I took the driver seat out and started to determine what I'm doing with the roll bar and belt mounting. There's a good 7 page thread here that is super helpful.

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I like this setup of horizontal bars: Post in thread 'RPM Rollbar install'
 

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Discussion Starter #38
2021.02.19: Finally got the last replacement part. Filling the coolant via the vacuum method took about 5 draw on it, my compressor is not the strongest. Other than doing it multiple times, it all seemed fine. Filled the oil. Double checked all bolts, visual inspection, checking the pile of replacement parts for anything else not done or should be back on.

Then the moment of truth: starting the car! It was all fine. Less clattery than before, of course the new guides. Temps looked OK, tho the air was quite cold here in PA, so the fan didn't kick on but temps stabilized at 188.

I'd embed a movie here but its too much work to post on YT for a 30s video.

Here's my setup for Werks bar I'm modifying. Having a friend weld it soon. I will probably cut the exhaust just in front of this brace and splice it with a wide strap joint so I can take the front part off without having to continually take this rear brace off.
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My frame brace never had that WRP logo on it. It came without it.
 

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also I like what you did with your socket in order to see the size on it. The new set of sockets I just got are almost impossible to see the size on. I took black epoxy paint and sprayed the sockets where the writing is and once dried use a socket to drill adapter to attach them to my drill. Put a piece of 800 grit in my hand wrapped around the socket and pulled the trigger. So now the writing is really visible with the black on chrome.
 
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