Keeping the front end "down"/hill climbs/Instant Center... - Page 6 - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > General Technical Discussions > Advanced Jeep Tech > Keeping the front end "down"/hill climbs/Instant Center...

Stainless Steel Door Hinge PinsPoly Door Hinge BushingsFS: 2007-2013 Jeep Wrangler "HALO" Angel Eye Kit

Reply
Unread 12-20-2011, 11:14 PM   #76
ftgiles
Registered User
 
Join Date: Jun 2008
Location: Phoenix, AZ
Posts: 1,595
If you guys are mapping out suspensions that use a track bar, you're using the wrong calculator. The track bar sets the roll center height.

ftgiles is offline   Reply With Quote
Unread 12-20-2011, 11:45 PM   #77
ftgiles
Registered User
 
Join Date: Jun 2008
Location: Phoenix, AZ
Posts: 1,595
Quote:
Originally Posted by Imped View Post
Ftgiles said it perfectly a while back: "It's not the length of the arms that matters so much as the mounts at either end" or something along those lines. The relationship between the mounts (pivot points) determines the behavior of the suspension.
Here's my quote:

"Talk'n about long arms vs. short arms is silly. The arms need to be long enough to go from point a to point b. Spend your time figuring out point a and point b."

You'd think that's just stating the obvious, but hey, glad you liked it.
ftgiles is offline   Reply With Quote
Unread 12-21-2011, 06:07 AM   #78
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,250
Quote:
Originally Posted by flip2spin View Post
Lets see some numbers........ and its just your opinion that what you run works unbelievably well..


as for your TIP I do think past that but Im yet to see REAL facts (meaning numbers )
I'd gladly show you my numbers if I could get my files to load, which I can't. What you obviously don't understand is unless you know EXACTLY where your COG is at any given point, then the numbers will only be estimates. The outputs are only as good as your inputs. I use the calculator as a "first article" verification tool and go from there. What matters more than the final numbers is how I arrived there and what conventions I followed to arrive at the final setup. And until you understand that, you'll keep uselessly asking for numbers that you won't receive. As for my suspension working well.....I suppose you could call that opinion but the FACT of the matter is that it hasn't produced a single hop yet, is as smooth transitioning as anything else out there, and is overall the total opposite of my previous setup. So unless you just flat out don't trust me then you've got no reason to not take my word for it.

Here's a decent video for you showing the no-hop action:

I've never made it up that wall after 50+ attempts but it's certainly not the fault of the suspension. There's just a huge lack of traction due to sand and water....and the MTR's are at 8 psi. It's also a good demonstration of the front end going light when I come back down--I don't think the video does it justice but that wall is as sketchy as about anything.
__________________
OlllllllO
Float Test Build
IndyORV
Imped is offline   Reply With Quote
Unread 12-21-2011, 10:06 AM   #79
Robert J. yates
Registered User
1998 TJ Wrangler 
 
Join Date: Jan 2003
Location: mars
Posts: 2,962
Quote:
Originally Posted by flip2spin View Post
Lets see some numbers........ and its just your opinion that what you run works unbelievably well..


as for your TIP I do think past that but Im yet to see REAL facts (meaning numbers )
You don't need numbers in order to be able to tell whether or not a long arm kit is going to work. If you have been following this thread and the graphs posted, simple visual analysis will tell you that most if not all standard long arm kits have very poor link location. Its been said before but since it has not sunk in.... long arm kits are designed for ease of packaging with most having a high degree of link separation at the axle and little to none at the frame. If you want numbers, enter the kit of your choice into a calculator and then you will see what we are talking about. If you really want long arms, you are going to have to go custom to get them right.
__________________
Quote:
Originally Posted by samgm2 View Post
And yes, I am an exceptional scientist and engineer.
Robert J. yates is offline   Reply With Quote
Unread 12-21-2011, 10:13 AM   #80
pcoplin
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2008
Location: Beaverton, OR
Posts: 1,682
RaggedOldMan, You really need to get those numbers in the calculator so it can calculate the AS line so you can get your actual antisquat, then you can play with the numbers and see what pulling the pucks will do. You may be able to just redrill the lower axle mounts a bit higher and not have to pull the pucks. Or, make new mounts to raise them up, just need to be cognizant of the vertical separation.

I built my triangulated midarm in 06 or 07, and got lucky I guess. Works very well in the slow stuff. There's only so many places to mount stuff, and when you get longer arms, everything being equal, you get better geometry. The long arm kits just go too far IMO.

I calculated this just a couple years ago so I see what the "numbers" were. Here is my current setup:



Lowish antisquat, high roll center. Very stable off camber and no hopping, even when all four tires are on rocks. Problem is, with the higher roll center and upsloping roll axis, it causes body lean at speed. Combined with too-soft rear springs, it's a roly-poly pig at speed.

Triangulating the lowers will flatten the roll axis, making it more neutral at speed (along with higher rate rear springs).




As a rule of thumb, the higher roll center you have, the better off-camber stability you'll have, and the lower roll center you have the better it will handle at speed.

Here's a post of one of those threads from Pirate4x4 on roll axis that I've had saved:

The roll centre is the point that the body wants to rotate about on the axle or the point that the axle supports the body laterally (or supports the body in a sideways direction). The simplest example is a triangulated 3 link with the upper links triangulated to a single point on top of the axle. This point is the roll centre. If you are talking about roll centre what most people are concerned about is the height of the roll centre. If the roll centre is high it will reduce the amount of body roll that you get when on side slopes. This is a good thing because it keeps everything stable in the off camber stuff and is why a lot of people try to get their roll centre up high - to reduce body roll. The roll centre can be thought of as the point where the body is supported laterally (or sideways). So that if the body is supported laterally up high it wont have as much tendency to induce body roll than if it was to be supported down low. If a rig uses a panhard rod then the roll centre is the mid point of the panhard rod.

When you start to look at triangulated 4 links things start to get a bit more complex and you should be really talking about the roll axis as apposed to a single point. But in simple terms if only the upper links are triangulated then the roll centre is high (means less body roll) and if only the lowers are triangulated then you get a low roll centre (means more body roll). If both the uppers and lowers are triangulated then the height of the roll centre will still be high and the angle of the roll axis will be more horizontal. Now without going into it too much a horizontal roll axis produces little roll induced rear steer (which may or may not be usefull on a rock crawler). Also if you can get the roll axis to be sloping down a bit (going from the rear to the front) then it will behave better on the road (again this may not worry you on you trail rig)

Again this is hard to explain without going into things too deeply or writing 1000 words.

To further complicate things a high roll centre (or axis) isnt the be all and end all of rock crawler suspensions because what a high centre also does is if a wheel moves upwards (over a bump) then the body must move sidways as well (really should be drawing pictures here to help explain this). Now as you go faster for the wheel to move upwards quickly it must push the bodysidwards quickly as well - which is hard to do. What this means is that when you are throttling up a climb quickly (still talking rock racing speeds here ie say 40:1 and 4000rpm) when you hit a bump on one side your springs wont want to compress when you have a heigh roll centre because to compress a spring it must move the body sidways as well so you may as well think of it as having no springs at all and the rig will just bounce off the tyre.

Running a low roll centre will let a wheel compress much more easily without pushing the body sidways as much.

Lots of successful comp buggies run high roll centres and lots of then run low roll centres. One isnt definately better than the other.

So in summary:

If you want a high roll centre trianglate the uppers.

If you want a low roll centre triangulate the lowers.

If you want the rig to behave well on road at speed then you should look at triangulating both the uppers and lowers and try to get your roll axis sloping downwards a bit towards the front.

If you want to minimise roll induced rear steer then you should also do the double triangulated thing to get a flat roll axis (although having the axis a bit up hill or down hill wont matter just as long as its flattish).

If you want your suspension to work well on the heigher speed throttling climbs and soak up bumps then you should go for a low roll centre.

If you want your rig to work well on the slower crawling speeds and reduce body roll and remian stable in the off camber stuff then you should go for a high roll centre.

Finally the hieght of the roll centre or the angle of the roll axis wont really make a huge difference to the capability of a rig - we are only talking degrees here. Lots of very good comp buggies run every variation of roll centre and axis.
__________________
98 TJ 5.9/46RE/D300
85 Wagoneer 5.2/44RE
01 F250 Powerstroke 7.3/ZF6
Ultra4 KOH #689 car
pcoplin is offline   Reply With Quote
Unread 12-21-2011, 10:17 AM   #81
pcoplin
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2008
Location: Beaverton, OR
Posts: 1,682
Quote:
Originally Posted by Imped View Post
Read what I've said a little closer. Stock mounts do not provide crappy geometry if you stay low. Short arms do not automatically denote crappy geometry. I run short arms, just in a somewhat unique application and it happens to work unbelievably well.
It is true that short arms will behave very well when designed properly as yours is. The problem is when the suspension cycles, short arms are much more apt to have bigger changes. When your suspension is drooped you will reach higher AS numbers more quickly than mine, making that jacking and hopping possible. Roll steer can also be an issue. With longer arms, this won't happen to the same degree. Does it matter really? Probably not, but it's something to be aware of when building a suspension for yourself.
__________________
98 TJ 5.9/46RE/D300
85 Wagoneer 5.2/44RE
01 F250 Powerstroke 7.3/ZF6
Ultra4 KOH #689 car
pcoplin is offline   Reply With Quote
Unread 12-21-2011, 10:41 AM   #82
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,250
Quote:
Originally Posted by pcoplin View Post
It is true that short arms will behave very well when designed properly as yours is. The problem is when the suspension cycles, short arms are much more apt to have bigger changes. When your suspension is drooped you will reach higher AS numbers more quickly than mine, making that jacking and hopping possible. Roll steer can also be an issue. With longer arms, this won't happen to the same degree. Does it matter really? Probably not, but it's something to be aware of when building a suspension for yourself.
Good point that I hadn't made. The shorter the arms, less of a margin of error you're dealing with. The rate of change will be greater so the general rule in that case is to try to make the lowers as flat as possible.
__________________
OlllllllO
Float Test Build
IndyORV
Imped is offline   Reply With Quote
Unread 12-21-2011, 12:18 PM   #83
ftgiles
Registered User
 
Join Date: Jun 2008
Location: Phoenix, AZ
Posts: 1,595
Quote:
Originally Posted by Imped View Post
Good point that I hadn't made. The shorter the arms, less of a margin of error you're dealing with. The rate of change will be greater so the general rule in that case is to try to make the lowers as flat as possible.
And there in lies the problem that is so hard to flush out...

Short and flat becomes increasingly mutually exclusive as the suspension height increases.
ftgiles is offline   Reply With Quote
Unread 12-21-2011, 12:25 PM   #84
pcoplin
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2008
Location: Beaverton, OR
Posts: 1,682
Quote:
Originally Posted by ftgiles View Post
And there in lies the problem that is so hard to flush out...

Short and flat becomes increasingly mutually exclusive as the suspension height increases.

I agree. Plus, just making flat arms isn't the answer, or else you'll have a squattin' desert Jeep.

Well, unless that's what you are going for. Light rigs with little or no antisquat can climb pretty well, AND haul ***...
__________________
98 TJ 5.9/46RE/D300
85 Wagoneer 5.2/44RE
01 F250 Powerstroke 7.3/ZF6
Ultra4 KOH #689 car
pcoplin is offline   Reply With Quote
Unread 12-21-2011, 12:34 PM   #85
freeskier93
Web Wheeler
 
freeskier93's Avatar
1997 TJ Wrangler 
 
Join Date: Oct 2009
Location: Longmont, Colorado
Posts: 6,551
This has turned into a great thread and has helped further my understanding of 4-link geometry and will greatly help when the time comes (hopefully this next summer). I also hope I did not confuse anyone with what I had to say at the beginning of the thread.
__________________
Build Thread
My life in 2010: Chronicles of painting my Jeep
Axle Re Gear and Swap

CU Boulder Aerospace Engineering
freeskier93 is offline   Reply With Quote
Unread 12-21-2011, 12:54 PM   #86
pcoplin
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2008
Location: Beaverton, OR
Posts: 1,682
The whole moral of the story is: short arms on a lifted Jeep sucks a large bowl of dicks. They're fine for lifts less than 2 inches, and maybe 3 if you can accept unstable handling characteristics in low range, but I'm sure not. I'm not quite sure of the surge of short arm love (probably the new fangled "LCG" thing of not lifting the Jeep) but I'm sure glad I got rid of my short arms years ago. I just got tired of jacking, hopping, and all-around unpredictable behavior. I enjoy a neutral handling rig that will do what I think it will do. I got a lot more sure of the Jeep's ability after I designed my current suspension.
__________________
98 TJ 5.9/46RE/D300
85 Wagoneer 5.2/44RE
01 F250 Powerstroke 7.3/ZF6
Ultra4 KOH #689 car
pcoplin is offline   Reply With Quote
Unread 12-21-2011, 01:04 PM   #87
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,250
Quote:
Originally Posted by ftgiles View Post
And there in lies the problem that is so hard to flush out...

Short and flat becomes increasingly mutually exclusive as the suspension height increases.
Yes it is. It's not difficult if you stay conscience about height. I'm at 19" at the belly with 3* lowers.
Quote:
Originally Posted by pcoplin View Post
I agree. Plus, just making flat arms isn't the answer, or else you'll have a squattin' desert Jeep.

Well, unless that's what you are going for. Light rigs with little or no antisquat can climb pretty well, AND haul ***...
That's why I said "general" rule of thumb. No it's not the sole answer (uppers matter, of course) but when dealing with 17" lowers, it sure helps put the AS where you want it. My uppers are almost perfectly flat at ride height and the lowers are at about 3*. Separation at the axle is 8" and if I remember right, 6" at the frame.

Here's an older picture with the old truss--full droop, lowers @ 20* and axle still centered


Overhang


New truss/upper link mount setup
__________________
OlllllllO
Float Test Build
IndyORV
Imped is offline   Reply With Quote
Unread 12-21-2011, 01:10 PM   #88
Robert J. yates
Registered User
1998 TJ Wrangler 
 
Join Date: Jan 2003
Location: mars
Posts: 2,962
Interesting thread to say the least.... while calculators, link length and location all have been discussed, the one thing that hasn't is where the spring perches sit in relationship to the axle and frame. Even stock, TJ springs exhibit a bow and that is only further exacerbated when you add lift. I can say for certain that once we got the spring standing straight up and then moved the shocks.... my rig became much more pleasurable to drive as it is alot more predictable. Yah we went mid arm but I also think its a sum of the parts improvement and not just better arm geometry that has played into the improvement.
__________________
Quote:
Originally Posted by samgm2 View Post
And yes, I am an exceptional scientist and engineer.
Robert J. yates is offline   Reply With Quote
Unread 12-21-2011, 01:13 PM   #89
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,250
Agreed Robert. I feel like outboard mounts and straight coils should be a prerequisite to all of this....or at least done at the same time.
__________________
OlllllllO
Float Test Build
IndyORV
Imped is offline   Reply With Quote
Unread 12-21-2011, 01:49 PM   #90
pcoplin
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2008
Location: Beaverton, OR
Posts: 1,682
Quote:
Originally Posted by Robert J. yates View Post
Interesting thread to say the least.... while calculators, link length and location all have been discussed, the one thing that hasn't is where the spring perches sit in relationship to the axle and frame. Even stock, TJ springs exhibit a bow and that is only further exacerbated when you add lift. I can say for certain that once we got the spring standing straight up and then moved the shocks.... my rig became much more pleasurable to drive as it is alot more predictable. Yah we went mid arm but I also think its a sum of the parts improvement and not just better arm geometry that has played into the improvement.
I did the coil spring bucket relocation before the outboard to see if I could tell a difference, and couldn't. Probably helps with spring life, but I didn't feel any difference.


edit: I also believe the outboarding shocks is a very minor change in comparison to changing the link design. I ran my triangulated 4-link for 4 years without outboarding, and besides having more damping, it didn't change handling much. It mainly allowed me to have more shock travel.
__________________
98 TJ 5.9/46RE/D300
85 Wagoneer 5.2/44RE
01 F250 Powerstroke 7.3/ZF6
Ultra4 KOH #689 car
pcoplin is offline   Reply With Quote
Reply
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.