Outer Limits 4x4 Board

Hi all, my name is Matt Dunk and I thought I might do a bit of tech on setting up your coil overs in your rigs. I will start of by saying what I have learned over the past few years has been a mixture of oz rigs and usa rigs. This will be a basic all round look at do's and don'ts. Remember if you don't have nothing nice to contribute to this topic just don't contribute.
This is a discussion about how to set up your coil overs it is not designed to make enemies. If I feel the thread is going off topic I will ask for the whole thread to be removed.
However, open to discuss any ideas you have or have done in the past.

springs hold the rig up. most people think that if the rig is bottoming you put a much larger spring rate in to stop the rig from bottoming. If you keep adding spring rate to your rig to stop it from bottoming you will find that when you go off road the rig rides ruff and does not flex at all. Like i said in the beginning springs hold the rig up at ride height. if the springs are to soft the rig will not matinee ride height.

Basic rules of thumb I follow,

angles of 15deg in 15deg back are a good starting point to maintain good shock angle throughout articulation.

Mounting point material and angles of mounts should reflect the rigs weight and intended use.

40%up 60% down is a good all round setup.

Conventional Coilover nitrogen pressure should maintain around 200psi

Limit straps and bump stops are not just for looks.

Valving is all the difference between a hard or soft ride

Geometry :

Double triangulated 4links are the best if you are able to package it.

Top links must be atleast 85% the straight line length of the lowers to maintain useable pinion angle.

Separation at the frame should be 1/2 or less than separation at the axle

Your separation at the axle must be a factor of your tyre size, in most cases 8+" above axle centerline is sufficient.

We're fairly blessed to get any knowledge you have for free Matt, keep it coming!
So I'm led to believe most of the cars in the states are sprung so soft you can push them down half way through their travel, but they use shock valving and sway bars to control the car over bumps. Is this pretty much the case??

Thanks for starting this Matt. A couple of questions that might be of value to the discussion -

1. Should the coils be long enough that they are still in slight compression at full extension?

2. What are your thoughts on split rate coils vs two coils of the same rate o the shock?

3. For those of us running additional bypasses, how do you like to valve the coilover ?

4. During static droop on the chassis table how much short of full shock extension should the limit straps be set to account for stretch during dynamic droop?

5. What are your thoughts on running a third "keeper" spring

M

i think it would be better at this stage to discuss the basic before i answer all the individual questions, but keep them coming so that i can see where people are having troubles.

ok so we have so softer springs in the rig. the springs will have some preload on them at full droop. the amount of preload will change a little from rig to rig, depending on shock angle and location. eg on the link. on the diff, laying over a little to much and if you have large weight changes, fuel, spares, 4 persons in the rig.

you will find that the rig will not like to climb, or drive forward without trying to pull a front wheel and, or roll over and play dead. that is because it is easier to twist the chassis away from the diffs than drive forward. big ratio in the transfers will have a larger affect on its also.

ok if that all makes sense we can move on to the fix. put a sway bar on the rear and the sway bar will apply more poundage to the corner that is have trouble holding the rig up in this instant. so it is like you have put your old heavy ass springs back in the rear of the rig. but when you are drive down the track with a little pace on and hitting bumps the sway bar is not adding spring poundage as the diff travels up and down over the bumps. the springs and shocks are carrying the rig along.

so the sway bar will improve your ride buy allowing you to run less spring, so the trick is to adjust the sway bar poundage so the rig will still flex, but not to soft because than the rig will not climb. when you see a rig and it is pulling wheels everywhere on small climbs it looks good in a photo but changes are that a rig with the suspension working right it would just drive straight up.

to recap all that. the sway bar will only add poundage to the rear of the rig in a side to side motion. when the rear diff moves up and down the sway bar does nothing. the springs and shocks do all the work. that is how we can run some nice soft springs and allow the suspension to move across bumps. this same sway bar idea can be used on a air-shock and single spring/ shock rig. eg Nissan. Toyota.

rockcrawler31 wrote:Thanks for starting this Matt. A couple of questions that might be of value to the discussion -

1. Should the coils be long enough that they are still in slight compression at full extension?

2. What are your thoughts on split rate coils vs two coils of the same rate o the shock?

3. For those of us running additional bypasses, how do you like to valve the coilover ?

4. During static droop on the chassis table how much short of full shock extension should the limit straps be set to account for stretch during dynamic droop?

5. What are your thoughts on running a third "keeper" spring

M

My start up info from Matt & Wayne (ZukIzzy on Pirate) & my own research.

1. Full droop springs should be still under preload of minimum 1" below static coil height.
2. I was of the opinion probably as most that your upper coil should be different (lighter) than main (lower). Not necessary but usually the case especially on heavier rigs. Say you have 100/100. The top spring will do the majority of initial bump control until the stop ring comes into play. Then basically your coil rate is doubled.
3. When you add Bypasses the coilover basically becomes a "coil carrier" so the valving is brought back to present the Bypass as the valving tool in the suspension system.
4. Depends on quality, width & length. Some suppliers should have the info on the elasticity of the straps. With the 50mm straps we have on Rick Nowlan's buggy we did some testing & the 20" strap stretched 1.5". But this depends on obvious weight of vehicle & diff. This info is based on 1650kg buggy & Dana diffs with the stretch test done on 3rd member side.
5. I have been told that if you need to have a 3rd stage helper you have incorrect spring setup which correlates with question 1.



brooksy

The adjustable spring divider, some say needs to be x at ride height and some say they sitting on it at ride height, meaning top coil locked out. They way im seeing it, means jack at speed, so do you tune that lockout by feel at speed?

Thanks for the the info and starting this Matt.
Not exactly a shock question, but this

Separation at the frame should be 1/2 or less than separation at the axle

From what I've seen heard over the years, this is largely dependent on a combination of wheelbase, arm angle and where you want your instant center.
IE do you want to drive an obstacle or wheel stand up it ?

I wrote out a big long story about up-travel, but when i pressed submit it disappeared. sorry will try later.

^^^^
Don't ya just hate that



brooksy

Matt copy text before posting so if it fails you just paste it in.

Sorry guys been a bit busy the last few months.
Lets talk about up-travel, down travel. how much shock shaft is showing at ride height. just say we are running a 14'' travel coil over. you want 7'' of shaft showing at ride height, so the shock will have 7'' of up travel and 7'' of down travel on a 14'' shock/coil over. sometimes this is hard to package in the rig you are working on but it will work so much better and will allow for more tunable suspension. the more tunable the suspension the better it will work overall. If you can not achieve 7'' up and 7'' down due to packaging we can tune around it within reason. so lets say you have 5.5'' up and 8.5'' down it can be made to work but will require more time in the tuning side of things because you have to do the same amount of work with less up travel to do it in. so for the best results set the shock at 50/50 at your desired ride height.
this is not the case for air shock rig as you are building and running the rig in just rock crawling, low speed, single hit/bump terrain. Most air shocks guys run them with a few inches of shaft showing at ride height and achieve pretty good results.

air bumps. if we are working on the front of a solid axle rig with 7 inches of up travel it is best to have the bump come in contact with the axle in the last 2ish'' of travel. the idea of the bump is to slow the axle before impact with the frame. the bump should bottom out just before the shock. so it is a positive stop before the shock bottoms out. if you have a 4'' bump stop it can be limited back to a 2'' bump stop with a internal spacer. this will allow you to have 5'' of suspension travel before the bump comes into contact with the diff. once in contact with the diff it will still have 2'' of shock and bump stop working together.
the idea of shorting/limiting the bump stop is to allow more shock movement before bringing the bump stop into play. if the bump stop comes into play sooner it can upset the chassis/ride of the rig. so in other words the bump stop is used the catch that last little bit of up travel where you hit that big, big bump/whoops a little to hard. so on a single shock setup it is a very big tuning apparatus and good bang for buck. Gas pressure will change from rig to rig and tuner to tuner.
location of the bumps stops should be out close near the wheels on a solid axle rig, the closer the bumps are to the center of the diff, the more chance you have of bending the diff housing on big hits.