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Unsprung Weight Reduction: 09-13 Forged Aluminum Knuckle?

26K views 137 replies 21 participants last post by  ctsv247 
#1 ·
Hey,

So, we have cast-iron knuckles. They weigh a LOT.



After talking to the lead designer at Speed Tech Performance, he recommended that I try installing the forged aluminum spindles from a 2009-2013 CTS-V on my car (which might require purchasing second generation upper control arms, since they use a threaded bolt to hold the upright in place), or contacting LG Motorsports to see if they might consider fabricating them for us.

What do you guys think? About 10 pounds less unsprung weight on the front wheels, plus potentially more room for larger wheels. Anyone know why this isn't possible, or why we shouldn't be pursuing this already?

 
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#105 ·
Would it be possible to make a tubular upper control arm that would make this a bolt in swap without the need for welding in supports or reworking alignment slots while still keeping "stockish" alignment settings?

And, just so I understand, if you could easily make a replacement control arm, would this spindle swap not only reduce unsprung weight but allow for a wider rim/tire combo up front?

If this is the case, could I pay you to make me some kind of template to work off of so I could have some control arms made?

Thanks for your efforts at pushing this forward!!!
 
#106 ·
The upper Arm isnt the problem, u just need to make a new lower arm. They are the most expensive with a core charge.

It is possible, i am just not in the mind set to create a new one. I can come up with a 5mm cuttin pattern to help u all adjust a little more. There is enough steel fir 5mm but 10-15 is too much for it.

Let me see what i get from my alterations and i will revert back...
 
#108 · (Edited by Moderator)
#109 · (Edited)
I am back, and i started to shift the slot outwards so i may benefit from more negative camber.

I increased the front by 10mm and the rear by 15mm, but i am keeping the slot opennng at 30mm total.
Wondering why you're taking out so much material. Did you measure your camber angle prior to doing this, or are you eyeballing it? The reason why I ask is because you can calculate how much longer the slots have to be:

Roughly, the UCA and LCA mounting holes are vertically displaced by about 500mm (~20"). You might want to check that--I measured the height of the STS spindle in my house and added about an inch on either end. Per basic trig, a 10mm longer slot should give you about 1 more degree of camber capability (arctan 10/500 = 1.146°). So, for instance, if you determined earlier that the STS spindle/V2 UCA maxed out at about -1.2 degrees of camber, now you'd have the ability to go to about -2.2 degrees. If you wanted to simply add 2.0 degrees of camber, regardless of what you had earlier, you'd need about 500*tan(2.0°) = 17.5mm longer slots. Do you think you need more?

While you're at it, would you mind measuring the shank (M14 IIRC) and underhead length of the LCA bolts? Like you, I think that it's wise to reinforce those slots once you open them up like that. Doubling the tab thickness on the outside will reduce shear stress on the bolt, as a bonus. Earlier this week, I purchased/received a 4x18" piece of 0.125" 4130 alloy steel for this very purpose. Since I will be welding one 2.25"-long piece (with slot to match) to each one of the 8 tabs, the bolt must pass through 0.250" = 6.35mm more material. Unless those bolts are longer than I remember, I think we'll want to purchase 5mm longer bolts to compensate. Otherwise there might not be enough bolt to fully thread each nut.

For anyone else reading this--you'll definitely need to POR-15 the sanded/welded area once you're done. Otherwise your subframe will rust. Amazon sells these little $25 starter kits that should be more than adequate to do the job, twice over. They come with everything you need, including brushes and gloves.
 
#110 ·
I eye balled it, but i did use a water level stick to see if i had any negative camber before i started, I had a little but couldnt tell if it was 0.5 or 1 degree. Since i was maxed out, it couldnt be more than 5 more milli till i got the desired negative camber, leaving 5mm more for wiggle room.

We will be fine with the 1/4" thickness. the bolts have more than enough thread to accommodate the new thickness.

We are prepping the frame and i disconnected the pcm for murphy's law. The Tig welder is calibrated and we will tac everything in and see if i get my desired negative camber...

Pix will come as promised, just need to take care of a few personal things...
 
#111 · (Edited)
I eye balled it, but i did use a water level stick to see if i had any negative camber before i started, I had a little but couldnt tell if it was 0.5 or 1 degree. Since i was maxed out, it couldnt be more than 5 more milli till i got the desired negative camber, leaving 5mm more for wiggle room.
If you don't already have one, a simple magnetic angle finder is really handy in times like these. Here's the one I use.

If you go digital, make sure you get something with a backlit screen. Because most of these things are made China, eBay is going to be your best bet.
 
#116 ·
Observation when you take apart the front suspension components it's best that you set everything up so that the lower control arm in the upper control arm our level with each other and then install the shock absorber this will help keep it where the shock absorber is a neutral tension.

Otherwise you will have either the upper rubber bushing or the lower rubber bushing exerting too much pressure
 
#118 ·
Help me understand why anything you do will hold true once the weight goes back on the car.

It looks like you could extend the lower control arm to the front control arm bushing by 10mm and to the rear bushing by 15mm and this would position the ball joint about where it needs to be.

I have to say that I am fine with elongating the bolt holes on the frame and then reinforcing them with 3mm plate but I have to say that I'm surprised you are Fuzzy after the reaming you gave Max over his drilled control arm bolts.....
I've drawn up a design and will be having my local machine shop cut eight 9/16" (14.29mm) slotted tabs out of 3" long, 1/8"-thick (3.175mm) hot rolled 4130 alloy plate steel. Right now, the slots in my drawing are 50mm long, but I'll finalize the drawing when I take my wheels off tomorrow. Ideally, you'd like to have the ability to go to -3.0 degrees of camber on the front wheels to accommodate future lower control arm upgrades that may alter your geometry slightly.

I think that machining these pieces is critical to ensure that you don't make the car a nightmare to align afterwards. Roughly-hewn slots (the kind of stuff that you'd make with a drill and a lot of patience) makes it hard to position the control arms smoothly when you're fighting the suspension for control of the wheels. Plus, 4130 steel is significantly stronger than A36--likely what the subframe is made from. If anyone else is reading this and is interested, let me know and I'll have duplicates made. It won't be cheap (maybe $75-100 including machining and shipping), but I think it'll be worth it. I can also POR-15 or powdercoat the plate if requested, but I think you're better off doing that yourself.

ctsv247, your question seems a little bizarre. Here, we're extending a slot in the subframe, which is certainly compromising the strength of the slot near the end since you don't have as much material left there. But then we're welding a piece of superior quality plate steel onto it that's twice as thick. The result is a subframe mounting point that is vastly stronger in that area than it was previously.
 
#117 · (Edited)
Just so I know....

If you made a new lower control arm that the distance between the bushing mounts and the ball joint were increased by say 20 to 30mm,you could make this a bolt in swap that would offer fairly stock alignment settings, decreased unsprung weight and allow us to run say a 285 tire up front??

Thanks for your efforts!

----------

Edit that last post....

It looks like you could extend the lower control arm to the front control arm bushing by 10mm and to the rear bushing by 15mm and this would position the ball joint about where it needs to be.

I have to say that I am fine with elongating the bolt holes on the frame and then reinforcing them with 3mm plate but I have to say that I'm surprised you are Fuzzy after the reaming you gave Max over his drilled control arm bolts.....
 
#119 ·
Bizarre? I've seen a lot of drilled suspension bolts over the years but modifying a frame is a bit more "outside the box" shall I say.

While I'm not there with you to complete this picture in my mind, I would reinforce the entire control arm mount area while you have it apart but I haven't thought this through as deeply as you have. I spent a lot of time off-roading trucks and it seemed to me that every time I thought I was being smart modifying one part of the frame, I usually unlocked weaknesses elsewhere and before it was all said and done, I had boxed the entire thing.

Weld on soldier.

----------

Almost forgot....based on your up close and personal experience with this project, how hard would it be to make a tubular lower control arm to make this a bolt on. In my current situation, it would be much easier to have all the fab work done off the car and not on it.

Thanks!
 
#121 ·
With the info gathered here, it shouldn't be too hard to fab a tubular lower control arm to make this a bolt in swap. Could be wrong but I doubt it.

I emailed Max at Creative Steel to see if I could peak a little interest in this as it would make a great complement to his already produced "wide tire rear trailing arms". If any one besides myself sees this mod as being beneficial and you (like me) don't have the time or resources to have parts machined and then weld them on, send Max an email and maybe we can convince him to add something like this to his product offerings.

Thanks to all who have pushed this forward.
 
#122 ·
It's not holding true as much as neutral position.

When u lift the car everythin pulls down, but when the car is sittin on its wheels the lca is level with the ground. As so should the uca be. If u tighten the uca in the level position then bolt everything on then the rubber bushing will work with ur shocks and not against it
 
#123 ·
Okay, so you're referring to an issue that is specific to the OEM bushings. Essentially, because the OEM bushings are bonded to the arms, once you torque down the control arm bolts, that rubber get twisted and tries to spring back to its original position as your suspension goes up and down. Torquing down those bolts in a "neutral" position minimizes the effect that the rubber twisting will have on the behavior of your suspension.

But then again, so does buying polyurethane control arm bushings. :stirpot:
 
#124 ·
FuzzyLogic said:
Okay, so you're referring to an issue that is specific to the OEM bushings. Essentially, because the OEM bushings are bonded to the arms, once you torque down the control arm bolts, that rubber get twisted and tries to spring back to its original position as your suspension goes up and down. Torquing down those bolts in a "neutral" position minimizes the effect that the rubber twisting will have on the behavior of your suspension. But then again, so does buying polyurethane control arm bushings. :stirpot:
So where does one get bushing for the upper and lower poly bushings?

Pot stirred
 
#131 ·
I am all installed, and i was seriously curious to know if i can have all four wheels 305. And Guess what?!?!?!?

I CAN INSTALL 305 ALL AROUND MY CAR!!!!

What does this mean for you, well, you can run a 275 up front.

http://www.flickr.com/photos/69163769@N07/13264231344/

http://www.flickr.com/photos/69163769@N07/13264238624/

http://www.flickr.com/photos/69163769@N07/13264027313/

I have an electrician coming in tomorrow to wrap up all my wiring needs, and install my gauge pod, methanol injection with temp activation, and rpm switches for my exhaust baffle control.

http://www.flickr.com/photos/69163769@N07/13264296974/
 
#132 ·
We could already run 275 on all 4 corners with the stock setup. so what size is that wheel? 19x10?
 
#136 · (Edited)
Basically, fuzzy decided to leave this forum and decided to take some of his info with him. In case he comes back and wipes everything out, i figured i would post on what i remember while its still fresh in my mind.

Basically, a sts spindle mounted on a v1 will yield more tire clearance on the front along with less unsprung weight. It's almost a bolt on. He used some specific combo of V2 and V1 upper control arms and mounts to mate up with the sts spindle but then discovered that the lower ball joint mount on the sts spindle wasn't where it needed to be in order to preserve stockish v1 alignment settings.

His approach to correcting this was welding lower control arm mount extensions onto the frame but the same could be done by making a tubular lower control arm to make up for this.

I'm sure I've left a few things out and got some of this a little twisted but its very close to reality. I hope to make this mod someday and when I finally get around to it, I'll post up but this is a worthwhile swap.

While its reported fuzzy got his car up and running he wouldn't specify about the success or failure of this project so ill assume he didn't get around to completing it.

Thanks to all who have pioneered this swap.
 
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