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Unread 10-03-2012, 06:38 PM   #1
cycleguy04
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Suspension Geometry

Doing a little research about suspension geometry I came across an AEV writeup entitled "12 Things To Know About Lifted Suspension Engineering".

Obviously they're going to throw in some "we do it this way and they don't" finger pointing, but I actually learned a lot from reading it.

It would be great if somebody in their infinite knowledge of suspension would shed light as to what exactly I should be trying to accomplish when it comes time to weld on brackets of my new axles. As the Jeep sits now, the springs are way off in relation to their perches and the Jeep has a horrible rebounding effect after bumps.

What I want to set up is a 4 linked rear and Anti-rock front and to correct some poor angles in the shocks and springs. I will be using 4" springs, but don't know which ones to use. Likewise for shock size.

Any recommendations, shared knowledge, pictures of your setup, etc. would be greatly appreciated.

Helpul link added at post 176: http://www.4wheelunderground.com/Suspension-411.html (helps with the vernacular)

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Unread 10-03-2012, 08:00 PM   #2
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A good thread: http://www.pirate4x4.com/forum/gener...s-dummies.html

My rear suspension:




Here are some very 'general' items that, put simply, will help result in a nice-performing suspension on and off the road
1) Flatten out those lower links. Keep the axle end tucked up for a) clearance and b) minimized angle
2) Keep the roll center as high as you can get it for minimized body roll
3) Keep the roll axis angle as neutral as you can get it--this is a function of the ratio of triangulation between the upper and lower links and vertical separation. If you look at mine, the lowers are triangulated at 10 degrees and the uppers are triangulated at about 25 degrees

Simply put, when viewed from the side you want the uppers to be parallel to the ground or close to it and the lowers to be slightly angled (less vertical separation at the frame than the axle, general number is 75% ratio).

Don't overthink the numbers and don't obsess over the calculator. I use the calculator as a visual aid and a loose verification tool, that's it. Understand where the numbers come from and how they're derived and gain a true understanding of the geometric concepts and you'll have no problems being able to quickly analyze a suspension and determine how it will work without using a calculator.
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Unread 10-03-2012, 08:11 PM   #3
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basically, you'll need bacon and titties and everything should follow suit




a big misconception is that swaybars are not useful offroad, which is quite the contrary. stock front swaybars are not useful offroad, stock rears are surprisingly adept at maintaining proper articulation. the main issue is that the stock rear swaybars are undersized as they're basically pre-determined to only be a minor aid to the suspension when the front swaybar is disconnected. its been practiced in wranglers for a long time before the advent of the e-disconnect in the JK rubicons.

a proper coil-linked suspension will be running front and rear anti-rocks.
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Unread 10-03-2012, 08:37 PM   #4
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Quite the nefarious cast of characters that you're attracting, here...

For starters, I'm going to agree with Imped: once you know what the linkages do and how they interact, you'll be able to walk yourself out of The Great Suspension Desert with relative ease...providing that you have a starting point from which to ask.

The starting point you need in order to ask specific questions comes from answering the "what I should be doing when it comes time to weld" statement that you posted earlier. The truth is that nobody here - nor anyone else anywhere outside of the space you occupy in the left-hand seat of your rig - can adequately address that concern. You have to determine your goals and then reconcile those goals with the inherent purposes of a vehicle's suspension. As taken from "The Coilover Bible"...

"An off-road vehicle's suspension system is designed to perform these basic functions:

1. Support vehicle weight / maintain correct vehicle ride height.
2. Keep the tires in contact with the trail.
3. Provide comfortable ride for driver & passengers.
4. Prevent or reduce damage to chassis from force of impacts with obstacles (including landing after jumping).
5. Maintain correct wheel alignment (locate the axles)."


That's what the suspension has to do; how it does those things can vary to an infinite degree. Once you have a goal in mind, you'll be in solid shape to simply lay it all out and pretty much know how it's going to work.

So, the big first question is "what are you doing to do with the rig?" A secondary question is "what needs to change in order to reach my goal, and why does it need to change?" You're on the right path by realizing that your spring/shock arrangement might not be optimal...so now it's just a matter of continuing those question/answer sessions until the lightbulb flickers to life.

Also: yeah...bacon and boobs do in fact make things better. And waffles...those help too.
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Unread 10-03-2012, 08:52 PM   #5
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Originally Posted by spyder6 View Post
basically, you'll need bacon and titties and everything should follow suit
Two things I just happen to have at my disposal! This should be a piece of cake.
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Unread 10-03-2012, 08:53 PM   #6
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Originally Posted by Sundowner View Post
Quite the nefarious cast of characters that you're attracting, here...
what are you trying to say??
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Unread 10-03-2012, 09:09 PM   #7
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My Jeep is and will remain a daily driver, so onroad drivability is foremost. That said, I want it to excell on unimproved, gravelly, pot holey roads and be capable of some serious wheeling three or four times a year. Thanks for the help, guys.
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Unread 10-03-2012, 09:12 PM   #8
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here is my old TJ with the front swaybar connected, perfect example of how it then forces the rear suspension to work for it while the front suspension lollygags



this is NOT how it works when you have an antirock lol
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Unread 10-04-2012, 12:09 AM   #9
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Lots of good advice above. I'm heading to Rimrock on the 12th for the day to set up camp, then will return for a couple weeks a day or two before big bull opens and remain till end of season. If I get there early enough on the 12th and if my health allows me to get the tent up early enough, I'll be testing some of the easier trails with the rig till around 4:00pm. You're welcome to stop by camp as I'll be wheeling for the duration looking for elk. Only one cow tag in camp, rest of us are spike only unfortunately. There will be plenty of wheeling "Rimrock" style if you're up to it. Expect breakage and body damage at minimum however depending on conditions. All pending my health allowing the trip of course.

One thing that hasn't been mentioned is once you read all that stuff, use the calc, THINK you have it all figured out, you'll then move to start burning in your mounts. At that point you'll discover none of it works and you're left to deal with what you've learned from the above vs. what actually fits in your TJ's frame constraints, with the axle limitations, the body, fuel tank, steering, etc. and whatever else you feel needs to be kept or eliminated to make it all work.

I had a good plan on paper for my rig but ended up changing most of it due to space limitations. It still looks good on paper, but not what I'd originally planned. The thread on Pirate posted above, and many other threads as well I'd searched over the years all pointed to similar directions. I made due with what I could fit. I knew I wanted up travel in the shocks, I knew I wanted 12" travel shocks with 6" up and room for more if need be, I knew I wanted as much clearance as I could realistically gain and I knew I wanted it to behave on the street yet remain planted on the steep nasty off-camber hill climbs we have here all over WA. On paper I'm about a 72% AS with a slightly negative neutral roll steer. -0.0xx if I recall??? Forget exactly. My rears are I THINK 6 degrees, my fronts about 4 degrees-if I recall, I forget exactly. Rear uppers are parallel to ground 0 degrees and I can't say on the 3 link front, I just put it where it fit. I think I have around 6-6.5 VS at the frame and around 8-8.5 at the axle on the rear, my front 3 link is all but totally parallel with the lower.

What I've learned is I don't know jack about doing this type of thing and didn't know jack about suspensions before hand either. I THOUGHT I had a good ride before, but knew there were several things that I THOUGHT could be improved on. Keep in mind I'd been through 3 prior suspension swaps. This was my first REAL build. I retained the same 3" springs I'd had for a few years that are well used yet stuffed a 12" shock under them and realized a solid 6" of up both front and rear but actually have room for about 7" in the rear and 6.5" up front. In terms of handling of the rig, it is FAR better than anything I've ever ridden in prior. This is the best it's ever been on and off road. It is firmly planted over the rough washboard gravel roads just getting to the trails at nearly double the speeds I'd been able to achieve prior but I'm certain much of that is due to the custom tuned shocks from Wayne. The combination between shocks and suspension design is worlds different than anything I had pre-packaged prior. It's planted now where it broke loose before, and remains planted at nearly double the speeds-at least to the point of what I'm comfortable driving anyway. Meaning some gravel rough washboard roads that I was lucky to hit 20-25 before and would be fish tailing on, I'm now hitting speeds of 50+ planted and braking for the turns. Is it design? Is it shocks? I believe it's both but I can't say for certain as I have no experience with any other custom design nor any other custom shocks and tune. I couldn't tell you what difference I'd feel in the seat with 65% AS and -1.5 understeer, nor could I tell you what 78% AS with +1.5 oversteer would feel like. I'm coming from the last at a measured 172% AS and 12 degrees over steer so I have a good idea of what direction it would lead, but no clue on the "perfect" setup or if there even is one. Again, space constraints will dictate what you can get away with and how far you're willing to cut things up. My frame is cut in multiple points, notched in some and boxed in others, my engine mounts are modified, truss cut, crossmembers cut, track bar mount ground, track bar gusset ground, gas tank and skid some 4" over stock and back, etc. How far are you willing to take this??? My rig is a dual purpose that runs both street and trail and it's the best it's ever been. With all the prior suspensions I'd had, I always felt there was something "more" and knew immediate things I'd wanted to correct. With what I have now, I'm left wondering what "better" would be and struggling to find anything that really needs changed. My direction is shifted now towards better tube work, custom seats with harness and safety stuff. I have no clue at this point what I would change in the suspension if I did it over. Likely nothing at this point. Is it perfect? Probably not but it works for me, I'm happy and that's what counts.

Some very generalized basics-

Cut and relocate your spring perches to straiten the rear springs.
Outboard the rear shocks-yes, that includes frenching the frame in addition to moving lowers. Lowers only won't cut it.
Optimize shock travel with whatever length you want to run-shoot for 50/50. With your 4" springs, I'd be certainly running a 12" shock with 6 up and 6 down without question. You can try for more, but with a good 4" spring, you'll be un-seating before the shock is extended and wasting travel. 12" is about the practical limit. If you need springs, Currie is an excellent choice. Shocks-pick your poison but I will say the Fox 12" remote res 2.0s with Waynes custom tune is unbelievable. I have no clue how comparable Kings would run. Only Kings I've experience with were coilovers and I was never happy with the rates on them despite all the changes on that particular rig. It's not a fair comparison.
Uptravel IS important, find it.
Anti-Rocks are your friend. Use them-front AND rear.
Do NOT skimp on the parts used for this-not in the joints, not in the links, not in the shocks. Buy GOOD parts and you'll only have to do this once. Skimp on the tunes and disco lights to get good quality suspension components under the rig where it counts. This will pay off later with regards to the bacon and boobs.

Above all else, Have Fun!

Best of Luck,

Mike
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Unread 10-04-2012, 06:25 AM   #10
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I know Mike has already hit on it, but you don't even realize how much improvement can be made over the stock/stockish setup.....a good suspension like his or mine performs worlds better on AND off the road. My top concerns are how it handles, corners, and steers on the road and I use the best available parts to give me that, along with durability and minimal maintenance and fuss. Take care of how your rig does on the road and it'll take care of you off of it. If you ever hear a phrase along the lines of "on road and off road performance are mutually exclusive" call BS, because that's exactly what that thought process is.
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Unread 10-04-2012, 09:28 AM   #11
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what are you trying to say??
Seems like a similar group of people always seem to show up when the "S" word gets mentioned...which is a good thing because most of them (read: "not me") know what they're talking about. I see this as being very positive...all reputations aside, that is.

Quote:
Originally Posted by cycleguy04 View Post
My Jeep is and will remain a daily driver, so onroad drivability is foremost. That said, I want it to excell on unimproved, gravelly, pot holey roads and be capable of some serious wheeling three or four times a year. Thanks for the help, guys.
I'd not deviate too much from the stock setup, then. If you want to ditch the track bar in the rear, fine...I won't argue that one bit; I'll just second the recommendations that have been made thus far and refer you back to the picture that Imped posted above. Compare that photo to the diagrams in the four-link calculator screenshot, and you'll see that while the links are positioned differently from the stock setup the overall idea is pretty much the same. Better joints, better clearance and better angles on the links...that's HUGE improvement over stock and you really haven't done anything terribly radical, aside from making some of your links double up on their axle-locating duties.

Quote:
Originally Posted by Imped View Post
I know Mike has already hit on it, but you don't even realize how much improvement can be made over the stock/stockish setup.....a good suspension like his or mine performs worlds better on AND off the road. My top concerns are how it handles, corners, and steers on the road and I use the best available parts to give me that, along with durability and minimal maintenance and fuss. Take care of how your rig does on the road and it'll take care of you off of it. If you ever hear a phrase along the lines of "on road and off road performance are mutually exclusive" call BS, because that's exactly what that thought process is.
1000% agreement, here. After thinking on the matter for a bit, I believe you will come to the understanding that there is very little fundamental difference in what the vehicle's suspension is required to do on-road as opposed to off-road. Does it act in different ways at different times? Of course...but it does not deviate from those five basic rules that I posted earlier.
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Unread 10-04-2012, 09:31 AM   #12
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first rule of suspension club is that you dont talk about suspension club
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Unread 10-04-2012, 09:43 AM   #13
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Seems like a similar group of people always seem to show up when the "S" word gets mentioned
What can I say? It's a subject I thoroughly enjoy.
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Unread 10-04-2012, 12:08 PM   #14
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first rule of suspension club is that you dont talk about suspension club
Quote:
Originally Posted by Imped View Post
What can I say? It's a subject I thoroughly enjoy.
In case my original comment about the nefarious characters and the subsequent explanation wasn't clear enough, let me say this, now: that was a statement of respect. If it wasn't for you guys and a few others I'd be talking completely out of my a** on the subject of suspensions, which seems to be the de rigueur thing to do of late.

To that end, I'm pretty glad that this is a limited participation event thus far; I'm completely sick and tired of every thread on the subject devolving into people doing their level best to disprove everyone else on the planet. On the Tech forum this would be a six-page thread, and five pages of it would be reasonably-groundless rebuttals to the long and informative post that Mike contributed. Most of the rest of it would be people grabbing onto Imped's "call BS" statement because they don't have anything better to contribute.

Suspension talk is something I thoroughly enjoy as well...and when the right people are involved in the discussion I invariably learn something. Now all we need to do is type the word "coilovers" enough times, and a few more people will probably show up.
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Unread 10-04-2012, 12:09 PM   #15
cycleguy04
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Great guys! So I'm on the right track upgrading to Curry Johnny Joint control arms.

Imped, your lower control arm brackets look like they are mounted to the inside of the frame. Is that custom or did you get a bracket kit that was designed that way?
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