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Lowered Suspension: An Engineering Perspective.


This is a discussion on Lowered Suspension: An Engineering Perspective. within the Lowered forums, part of the 4th Gen : 2009 - Present category!
Ladies and gentlemen, it's time we had a REAL tech thread on suspension and lowering for these trucks. I proudly ...


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Old 12-19-2016, 10:53 AM   #1 (permalink)
 
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Default Lowered Suspension: An Engineering Perspective.
Ladies and gentlemen, it's time we had a REAL tech thread on suspension and lowering for these trucks.

I proudly present to you, this thread:


In all seriousness, I figured I would share some of what I've learned in one place, rather than scattered through the forum.


I'll try to use this OP as an Index of the various posts that are good info. I'm going to reserve the first few right now to edit as I go on.


Post #2: My experience and problems with the Belltech 2/4
Post #3: Cutting OEM front springs vs. Crown Springs
Post #4: Problems with Spohn Arms and potential alternatives
Post #5: The basics of rear suspension geometry and real world results of different mods
Post #6: The basics of front suspension geometry and real world results of different mods
Post #7: My final solution to the rear suspension on my truck
Post #8: My final solution to the front suspension on my truck

EDIT: This thread is going to be a little bit of a living document as time goes on. Gonna take me at least a day or two just to get everything in here.




Anyone have a set of corner scales I can borrow? Happy to pay for shipping if you aren't local. I just need to verify some stuff and get some real world numbers...


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Old 12-19-2016, 10:54 AM   #2 (permalink)
 
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To begin, a summary of what I've done.

Originally, this is what I purchased and installed:
Belltech 2/4 lowering kit without shocks.
QA1 single adjustable shocks.
Hellwig front and rear sway bars.
Spohn adjustable panhard bar and control arms.
Airlift 4" lowered helper air bags.

After letting it settle for a day or two, I took it to get aligned and couldn't get the camber back to 0.

Installed a set of Moog problem solver ball joints and got the camber back to zero, but they caused other issues. Because they make the upper control arm sit higher, they increase the camber gain as the wheel tracks up. Basically my wheels would go WAY in at the top every time my suspension compressed.

I drove around with that combination for a while, but had issues scraping tires against my wheel well liners up front. Eventually I blew my drivers side liner completely out. At this point, I decided to go back to stock springs and shocks until I could figure out the problem.

When I swapped back to OEM springs and shocks, I noticed the Belltech springs appeared to be a LOWER spring rate than the factory springs, which is a HUGE no-no when lowering a vehicle. I contacted Belltech and they informed me their springs are a 800 ft-lb rate.

Here's the thread that covers that whole debacle: 2/4 drop is a little low up front...


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Old 12-19-2016, 10:54 AM   #3 (permalink)
 
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That brings me to a couple weeks ago when I picked up a 1/2 Crown from Ak47bravo on here.

I installed the rear springs and there was a noticeable drop and stiffness difference, but in looking at the fronts I realized the Crown springs are nearly identical to the OEMs... The coils are slightly larger, the OD of the spring is a little bigger and the spring is a little shorter overall, but not by much. I took a bunch of measurements off the springs and calculated up the spring rates for them.

Here are some comparison pics between the Crown and OEM coils:







At the same time, I also looked into cutting the stock springs and what sort of spring rate that would produce. If you didn't already know, cutting the springs actually makes them stiffer. It makes sense because the spring is shorter, so there's less of it to share the load and deflect.



The formula here is: Spring Rate = (G*(d^4)) / (8*N*(D^3))
Where G is the torsional modulus, d is the wire diameter, N is the number of active coils, and D is the mean coil diameter.

As you can see, the Crown springs are only 6% stiffer than the OEM ones. Unsurprisingly, the Belltech springs are less stiff than the OEM ones.

What is slightly surprising is how much stiffer the cut springs are. By taking out a single coil, you get a 24% increase in the spring rate. This corresponds to about a 2" drop from what I've been able to see from people that have done it.

Knowing all that, I decided to cut my OEM coils.

I cut off one coil and put them back in, and the truck handles MUCH better. The coils are WAY stiffer than stock and the truck sits at least 2" lower up front. As with all these trucks, the driver's side is slightly lower. I may shim that spring slightly to get the truck level.

I also cut my rear springs, but I don't have any rate calculations on them yet, partly because they're a progressive spring and it's hard to figure out where the change in rates occurs. Originally I cut two coils off, but it still sat too high so I went ahead and cut a third. There's maybe one full low spring rate coil left, so I realistically can't cut any more of the rear off.

Here are the pics of how the truck sits now with one full coil cut from the front and three full coils cut from the rear:




After cutting the rear springs again, I attempted to align the front of the truck. Sadly, I didn't have enough camber or toe adjustment to get it correctly aligned, which was a fear of mine going into this. I pulled my tie rods off and cut a little bit from the end to allow me to bring the toe in a little bit, and it seems like it's pretty close now, but the wheel still sits juuuuust a little to the right. I may take another little bit off the end of the rod and try to align it again.

Here are some pics of how it sat after the first round of cutting the tie rod ends. The toe is damn near zero with it being just a hair off, and the camber is pretty close to zero too. I also think my rear axle is fairly centered left to right, which is surprising. You can also see in these pics how much higher my passenger side is, which is a little bit of a problem. I need to shim the drivers side back up.













After deciding that the rear still sat just a liiiiitle bit too high and realizing that I couldn't cut any more of the coil, I bought a belltech rear spring kit. I went ahead and just threw it in without taking any comparison pictures or measurements of the coils since I was in a hurry. Don't worry, I'll take all the measurements and pics when I put the crown stuff in.

Here's how it sits with the cut OEM fronts and the Belltech rears. I haven't cut any off the belltech either. I'll get some more/better pics, the sun in that one was unavoidable. Also, my drivers side now sits WAY lower in the back than the passenger side. I'm seriously considering a ballast of some sort. And yea, that's a big ass lifted truck in that pic. I'm pretty sure the bed of his truck was higher than the cab on mine...






Yes, that's a double rainbow.

My biggest issue right now is that the front camber is maxed out and I'm fairly sure I still have negative camber. I may see about devising a better way to solve that little issue. I'll keep you guys posted as time goes on.

I'm planning on swapping in the crown springs this next week and running with those for a little bit while I work with QA1 on possible coilovers. We shall see, but I need to take a bunch of measurements on the truck anyways, so this will be my opportunity. Might end up driving the vette to work for a week or so. Ah well.


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Old 12-19-2016, 10:55 AM   #4 (permalink)
 
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Another running problem I've had is with the Spohn lower control arms. Quite a few members have had issues with them clunking and requiring constant adjustment. This is a well-documented issue and doesn't require a ton of explanation from me here. Here's one thread on it: Spoon bars clunking

What I want to use this post to do is discuss other options and potentially custom arms based on the Spohn design along with some other stuff that I've seen. The idea would be to get a low cost polyurethane or rubber bushing arm that won't clunk, won't require constant maintenance, and will allow adjustment of the rear axle position.

Right now I have my old Spohn arms sitting on my workbench. I'm going to pull them apart and inspect the Del-Sphere joints along with taking some measurements. I'll try to draw something up in CAD and might take a crack at making some of these arms or something to that effect.


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Old 12-19-2016, 10:55 AM   #5 (permalink)
 
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On the subject of the Spohn arms and the rear suspension, I'm going to reiterate some of the basics of lowering the rear on these trucks like the axle position and so forth with this post, but I'm also going to go a little bit further and try to get some real world measurements and details so I can put them up here for everyone to see.


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Old 12-19-2016, 10:56 AM   #6 (permalink)
 
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This post will be a breakdown of the front suspension, similar to the above post, but with real world measurements and what not.


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Old 12-19-2016, 02:26 PM   #7 (permalink)
 
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Using this post to explain whatever it is I end up doing with the rear suspension on my truck.

Currently looking at a few different options:

1) Factory cut coils.
2) Ground force coils, either cut or not.
3) Possibly something a little crazy, like a custom fit adapter for a more common coil size or a coilover.

For option #3, I'm looking at something like this for a coilover:



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Old 12-19-2016, 02:26 PM   #8 (permalink)
 
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Aaaaaand this post for whatever I end up with on the front.

Currently looking at a few different options:

1) Factory cut coils.
2) Ground force coils, either cut or not.
3) Possibly something a little crazy, like a custom fit adapter for a more common coil size or just doing a coilover.

For option #3, I'm looking at something like one of these for a coilover:





Either one would likely require a little bit of custom work to get it to fit, but neither should be too ridiculously hard to adapt.


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Old 12-19-2016, 03:58 PM   #9 (permalink)
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Originally Posted by Dubstep Shep View Post
Another running problem I've had is with the Spohn lower control arms. Quite a few members have had issues with them clunking and requiring constant adjustment. This is a well-documented issue and doesn't require a ton of explanation from me here. Here's one thread on it: Spoon bars clunking

What I want to use this post to do is discuss other options and potentially custom arms based on the Spohn design along with some other stuff that I've seen. The idea would be to get a low cost polyurethane or rubber bushing arm that won't clunk, won't require constant maintenance, and will allow adjustment of the rear axle position.

Right now I have my old Spohn arms sitting on my workbench. I'm going to pull them apart and inspect the Del-Sphere joints along with taking some measurements. I'll try to draw something up in CAD and might take a crack at making some of these arms or something to that effect.
Something maybe worth looking into for those that have the adjustable Spohn arms.

I actually like the Spohn arms quite a bit except for the frequent adjustments and clunking, as many have stated.

My thought was to get an ID measurement of the stock control arm bushing ring, then find a way to machine out the threads/extra material on the one side of the Spohn control arms to either the same ID as the stock control arm where a stock rubber bushing(think Moog replacement) would be pressed in "or" if that ID was to large once the required material was removed, machine a weld-able bushing ring with the requisite OD and the same stock ID/width as a stock control arm ring.

In this case, you would have a serviceable bushing, low NVH, and an adjustable arm.


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Old 12-19-2016, 04:07 PM   #10 (permalink)
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Originally Posted by Dubstep Shep View Post
That brings me to a couple weeks ago when I picked up a 1/2 Crown from Ak47bravo on here.

I installed the rear springs and there was a noticeable drop and stiffness difference, but in looking at the fronts I realized the Crown springs are nearly identical to the OEMs... The coils are slightly larger, the OD of the spring is a little bigger and the spring is a little shorter overall, but not by much. I took a bunch of measurements off the springs and calculated up the spring rates for them.

At the same time, I also looked into cutting the stock springs and what sort of spring rate that would produce. If you didn't already know, cutting the springs actually makes them stiffer. It makes sense because the spring is shorter, so there's less of it to share the load and deflect.



The formula here is: Spring Rate = (G*(d^4)) / (8*N*(D^3))
Where G is the torsional modulus, d is the wire diameter, N is the number of active coils, and D is the mean coil diameter.

As you can see, the Crown springs are only 6% stiffer than the OEM ones. Unsurprisingly, the Belltech springs are less stiff than the OEM ones.

What is slightly surprising is how much stiffer the cut springs are. By taking out a single coil, you get a 24% increase in the spring rate. This corresponds to about a 2" drop from what I've been able to see from people that have done it.

Knowing all that, I decided to cut my OEM coils.

I cut off one coil and put them back in, and the truck handles MUCH better. The coils are WAY stiffer than stock and the truck sits at least 2" lower up front. As with all these trucks, the driver's side is slightly lower. I may shim that spring slightly to get the truck level.

I also cut my rear springs, but I don't have any rate calculations on them yet, partly because they're a progressive spring and it's hard to figure out where the change in rates occurs. They still sit too high though, and there aren't many more of the smaller rate coils left, so I may have to get a set of Belltech rear springs and cut those.

At some point I'll try to upload pics to this.
need some pics of that cut front coil on and off the truck brother!


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