Coil over shock set up technique - Pirate4x4.Com : 4x4 and Off-Road Forum
 
Pirate4x4.Com : 4x4 and Off-Road Forum  

Go Back   Pirate4x4.Com : 4x4 and Off-Road Forum > General Tech > General 4x4 Discussion
Notices

Reply
 
Share LinkBack Thread Tools Display Modes
Old 11-26-2019, 06:58 AM   #1 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
Coil over shock set up technique

I’ve been tuning my truck for about 8 years now and I’ve hit a road block that I’m sure many of you have also seen. I’m curious what some of you do to address this tuning hurdle.

This situation pertains to a single coil over shock (non bypass) and dual spring rates, focusing on rebound.

Following the standard spring rate setup technique, it’s simply not possible to get your rebound set correctly to handle both spring rates.

I.E. if you get it dialed for the initial rate, things get scary when the main spring come into play. Or, you compromise and your initial ride suffers substantially causing packing on all the small stuff.

It has made me realize that this is one of the biggest reasons for bypass shocks.

But, there has to be a better set up for single shocks. Less than a 200% step up? No step up?
weswes01 is offline   Reply With Quote Quick reply to this message
Old 11-26-2019, 08:12 AM   #2 (permalink)
Zeus of the Sluice
 
miguelitojeep's Avatar
 
Join Date: May 2006
Member # 73093
Location: Redondo Beach, CA
Posts: 4,465
I leave this to the professionals... send your shocks into AccuTune Offroad and be done.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Overbuilt 97 Wrangler | 40" Black Labels, 14" Fox Coilovers, Trailing Arm Suspension, Atlas 4.3, Warn Winch, fully caged and tested
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
#BajaJeep @BajaJeep_mike
miguelitojeep is offline   Reply With Quote Quick reply to this message
Sponsored Links
Old 11-26-2019, 08:21 AM   #3 (permalink)
Registered User
 
Join Date: Jul 2001
Member # 6170
Location: Atascadero
Posts: 1,824
I don't know much, but experience and research taught me that 200% step up on the spring rates is way too much. Mine felt like I was hitting the bumpstops. Dropping to a lower step up should help.

Everything is a compromise. I don't know if you can increase free bleed in the piston and hope it chokes off at higher speeds when your most likely using both spring rates? Flutter stack on rebound? Unfortunately springs are position driven and conventional shock valving is velocity driven.

Kevin
Ghetto Fab. is offline   Reply With Quote Quick reply to this message
 
Old 11-26-2019, 08:55 AM   #4 (permalink)
Zeus of the Sluice
 
Valley Auto's Avatar
 
Join Date: Aug 2006
Member # 78079
Location: Carmel Valley Ca
Posts: 3,606
We need more information. At least spring rates,lengths,travel and position. My guess would be something is missing from the initial setup. But also like mentioned above Ryan at Accutune is the man.
__________________
Master of the wire Wheel!
Valley Auto is offline   Reply With Quote Quick reply to this message
Old 11-26-2019, 10:25 AM   #5 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
Ryan is the man for sure. Unfortunately he stopped tuning help over the phone, and I totally understand why.

I’m using Shim Restackor. The response calculations are much better than my butt dyno. I’ve tried everything from bleed, to flutter stacks, to rate plates but simply can not get a zeta function of 0.7-1 for both rates.

This is more of a question on how do you control two different spring rates with a single velocity sensitive damper.
weswes01 is offline   Reply With Quote Quick reply to this message
Old 11-26-2019, 03:44 PM   #6 (permalink)
Registered User
 
Jeffh555's Avatar
 
Join Date: Mar 2001
Member # 3775
Location: Santa Cruz, CA
Posts: 1,316
If you want to make it that simple, the answer is that you compromise.
__________________
I wheeled twice this year, that might be a personal record.
Jeffh555 is offline   Reply With Quote Quick reply to this message
Old 11-26-2019, 04:36 PM   #7 (permalink)
Rolling Mod
 
Beat95YJ's Avatar
 
Join Date: Aug 2003
Member # 22176
Location: Redondo Beach
Posts: 41,134
Quote:
Originally Posted by Jeffh555 View Post
If you want to make it that simple, the answer is that you compromise.
There is this, and IMO try for the littlest change in rates you can get. The only way to make a big step up change work Is to use the top spring as a tender that collapses completely at ride height.
__________________
I can break a steel ball in a rubber room!

Companies helping me get dirty:

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

& Blaine


:tank:
Beat95YJ is online now   Reply With Quote Quick reply to this message
Old 11-26-2019, 10:56 PM   #8 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
Quote:
Originally Posted by Beat95YJ View Post
Quote:
Originally Posted by Jeffh555 View Post
If you want to make it that simple, the answer is that you compromise.
There is this, and IMO try for the littlest change in rates you can get. The only way to make a big step up change work Is to use the top spring as a tender that collapses completely at ride height.
Thank you. I kind of came to these conclusions but was unsure if others did as well. The reassurance really helps.

I’ll post some screen shots of what shim restackor shows
weswes01 is offline   Reply With Quote Quick reply to this message
Old 11-28-2019, 12:28 PM   #9 (permalink)
Registered User
 
Join Date: Jun 2001
Member # 5326
Location: Southwest Colorado
Posts: 11,076
What about eliminating the step up rate completely? Keep things consistent rate. What issue is the using the step up rate helping you with?
__________________
42 MB, 225, T18, big kid go cart with clown tires
92 Dodge W250 daily driver on 39s
Mieser is offline   Reply With Quote Quick reply to this message
Old 11-28-2019, 01:04 PM   #10 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
Quote:
Originally Posted by Mieser View Post
What about eliminating the step up rate completely? Keep things consistent rate. What issue is the using the step up rate helping you with?
That would allow you to get the best rebound response through out the stroke with a non bypass coil over.

The common trend has been to use a step up rate to help control bottoming.... mainly at slow shaft speeds where dampening rates are not significant, such as G-outs (2-5 in/sec).
weswes01 is offline   Reply With Quote Quick reply to this message
Old 11-28-2019, 04:00 PM   #11 (permalink)
Registered User
 
Join Date: Jun 2001
Member # 5326
Location: Southwest Colorado
Posts: 11,076
Quote:
Originally Posted by weswes01 View Post
That would allow you to get the best rebound response through out the stroke with a non bypass coil over.

The common trend has been to use a step up rate to help control bottoming.... mainly at slow shaft speeds where dampening rates are not significant, such as G-outs (2-5 in/sec).
My next question would be how much up-travel are you dealing with?
__________________
42 MB, 225, T18, big kid go cart with clown tires
92 Dodge W250 daily driver on 39s
Mieser is offline   Reply With Quote Quick reply to this message
Old 11-30-2019, 07:32 PM   #12 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
About five inches. 200/300 lb rates. 1250lb sprung corner weight.
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-07-2019, 03:57 PM   #13 (permalink)
Registered User
 
Join Date: Jun 2001
Member # 5326
Location: Southwest Colorado
Posts: 11,076
Quote:
Originally Posted by weswes01 View Post
About five inches. 200/300 lb rates. 1250lb sprung corner weight.
The 100# split might be getting close to blocking the coil if the transfer nut is set too far down?

Have you tried narrowing the split? That should make the step up rate change more manageable.
__________________
42 MB, 225, T18, big kid go cart with clown tires
92 Dodge W250 daily driver on 39s
Mieser is offline   Reply With Quote Quick reply to this message
Old 12-09-2019, 08:08 PM   #14 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
The stop is currently 1” below the slider
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-10-2019, 09:14 AM   #15 (permalink)
Registered User
 
Join Date: Aug 2011
Member # 196897
Location: Reno, NV
Posts: 126
I would raise the secondary rings so you have more travel in the initial rate zone and tune for that, let your last 1.5"-2" take that heavier rate to keep you from bottoming out. You might also want to look at some 2" hydraulic bumps if bottoming out is an issue.

Whats your use for the vehicle?
thedirtman is offline   Reply With Quote Quick reply to this message
Old 12-11-2019, 08:05 PM   #16 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
You obviously misunderstood the point of this post. This is Is what I’m talking about. The method you are suggesting does not work well for a single velocity sensitive coil over.

As a few people who are smarter than myself suggested dropping the step up rate, or setting the stop so drop travel is the only thing that sees the initial rate.

I’ll have to post some visual graphs. It might explain it better than I can. I’ll run the numbers, 200% step up might be able to work...

I just dug into a WP PDS shock on the rear of my KTM. Interestingly, the progressive rate hits its transition at rider sag or ride height. The soft rate is for drop only. Soft rates are low falling rates.
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-11-2019, 09:41 PM   #17 (permalink)
Registered User
 
Jeffh555's Avatar
 
Join Date: Mar 2001
Member # 3775
Location: Santa Cruz, CA
Posts: 1,316
Quote:
Originally Posted by weswes01 View Post
I just dug into a WP PDS shock on the rear of my KTM. Interestingly, the progressive rate hits its transition at rider sag or ride height. The soft rate is for drop only. Soft rates are low falling rates.
One thing that's counter intuitive, but can help when thinking about spring how some cars react to spring rate changes.

For a given ride height, a softer spring rate will have more spring force between full extension and ride height than a higher spring rate. This can help the with tracking, forcing the wheels to stay in contact with the ground.

I haven't looked closely at a WP PDS shcok, does it have position sensitive damping in rebound, or just compression? Where does the spring rate transition compare to the damping force transition?
__________________
I wheeled twice this year, that might be a personal record.
Jeffh555 is offline   Reply With Quote Quick reply to this message
Old 12-12-2019, 06:33 AM   #18 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
You are correct for the most part. The total force at ride height will be the same no matter what the rate is. In example, if your corner weight is 1,000lbs, that’s how much spring force is needed to hold the vehicle at ride height. It does not mater what the rate or the preload is. It’s above and below ride height that changes with spring rate. Stiff springs = heigh rising and falling rates
Soft springs = low raising and falling rates

The PDS shock is a bypass shock but uses two pistons and a needle. It’s similar to the king internal bypass coil overs.

The secondary piston does not come into play until just above the bump stop. It’s not much more than a hydraulic bump stop. The spring rate transition is at ride height.

Looking at the PS6 spring, the adverted rate is 7.1-9 kg/mm (measuring closer to 7.75 - 10.5 kg/mm). That is only a 135% step up rate!

Last edited by weswes01; 12-12-2019 at 06:37 AM.
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-14-2019, 12:13 PM   #19 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
visual

I took two screen shots of the response spread sheet. This is a 200/300 lb spring with the stop set 1" above the slider. 12" travel, 5" bump. All I change was the spring rate and adjusted "ride height" for the main spring.

The graph on the bottom and second from far right (zeta vs wheel position) is a good one to look at.

A zeta function of 1 is considered "perfect" rebound dampening, chassis returns exactly to ride height.

A zeta function of .7 is a lighter dampening but will give you the best traction because it will keep the wheels on the ground more. The chassis will raise slightly above ride height when it returns from the bottom of the stroke.

The graph on the bottom left shows the what shaft speed it take to bottom out and what shaft speed you will see as it returns.

For the record, I am not claiming to know the answers. I just think the way our community has been setting up single coil over suspensions should be re evaluated. There are definitely improvements to be had.

Beat95yj pretty much nailed what I am seeing. I wonder how a extremely light combined rate would perform as the axles fall away from the vehicle?
The only other thing I am considering is flipping the springs to achieve a step up ratio of under 200%



[IMG]Screenshot%208_zpstrgkg61b.[/IMG]


Last edited by weswes01; 12-14-2019 at 01:08 PM.
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-14-2019, 01:06 PM   #20 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
OK someone help a brotha here. How do I post photos these days?
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-14-2019, 04:25 PM   #21 (permalink)
Rolling Mod
 
Beat95YJ's Avatar
 
Join Date: Aug 2003
Member # 22176
Location: Redondo Beach
Posts: 41,134
Bump
Attached Images
  
__________________
I can break a steel ball in a rubber room!

Companies helping me get dirty:

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

& Blaine


:tank:
Beat95YJ is online now   Reply With Quote Quick reply to this message
Old 12-14-2019, 07:41 PM   #22 (permalink)
Registered User
 
Join Date: Jul 2001
Member # 6170
Location: Atascadero
Posts: 1,824
I R Dumb, what is the zeta value? What does it mean in real life? Its hard to make out what the graph is showing in the pic. I'm not familiar with that software. Why is a zeta of 1 perfect?

It is cool to have tools like this, but at the end of the day you need to corroborate software output with your seat of the pants in the vehicle. Have you driven the vehicle with one of these setups and how did it do?

Kevin
Ghetto Fab. is offline   Reply With Quote Quick reply to this message
Old 12-14-2019, 09:33 PM   #23 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
The funny thing is I had been tuning by feel for years. I also took all the advice given to me off this forum. Never really satisfied with the results I bought the program, which is not expensive.

After I spent the time learning the program and taking all of the tedious measurements, it basically told me I was ass backwards. I was running #35 rebound stack with two bleed holes. To get the numbers right, I would have to go to a #90 stack with three bleed holes. I laughed and almost reassembled my shock like it was. I stopped myself though, because I would be real asshole to spend time and money on something and not try it out. Sure enough, it was a significant improvement. I don’t think this program is spot on, but it’s much closer than most butt dyno’s. It easy to get way off track with tuning.

If your not good at math, just think of the zeta function as a target. Their website explains it all of your curious.
weswes01 is offline   Reply With Quote Quick reply to this message
Old 12-15-2019, 07:07 AM   #24 (permalink)
Registered User
 
Join Date: Jul 2018
Member # 852104
Location: South Central PA
Posts: 8
Quote:
Originally Posted by Ghetto Fab. View Post
I R Dumb, what is the zeta value? What does it mean in real life?
Zeta is the "damping ratio". It is never the "dampening ratio". Shocks damp movement. Dampening is what happens with things get a little wet.

The damping ratio describes the amount of damping, that is the amount of energy absorbed by the shock. A zeta = 1 is know as "critically damped". Less than 1 is "under damped". Greater than 1 is "over damped".

In real life, an under damped system will oscillate (bounce in a suspension application) until it settles out (decays). This is known as a decaying oscillation. Imagine taking the shocks off a car and driving over a speed bump with one axle. With the shocks removed there is still some damping due to friction in the joints or the rubber bushing (even tires), but it is a small amount relative to the shock. The car will bounce as it goes over the bump, but will eventually stop.

An over damped system never oscillates, but will take a long time to respond. Over damping on rebound can cause the shock to become fully compressed and you can run out of suspension travel while driving, usually fast. Over damping on compression causes a rough ride.

Critical damping is the border between the two. There is no oscillation or overshoot, but the system is slower to respond than the under damped case.

Wikipedia has a nice graph that shows the different damping ratio responses (search "damping ratio"). The Wikipedia article references a "second order response". This is just a way to model (write a formula to describe) the response of a system. It is a very common method using a second order polynomial also known as a quadratic equation. Step response for all kinds of system can be modeled this way from suspension to electronics.

The reason a damping ratio of about 0.7 is targeted in many applications is because this produces almost no decaying oscillation with a slight overshoot (this is the chassis raising slightly above ride height) that is tolerable because of the speed of the response. A faster response would cause too much oscillation and a slower response would just be slower. You want the system to response as fast as possible without too much oscillation. Zeta = 0.7 usually gets you there. This is what helps keep the tire in contact with the ground.

I think using the modeling program is a great approach. Much better than butt dyno. It might feel "good", but maybe it could be "great" and you never know that because the butt dyno says it's "good" and you stop there. Butt dyno are rarely well calibrated in multivariable systems. There is a learning curve, however, and most people don't have the patience or the background to take a more analytical approach.

OP, if you have some experience with Shim ReStackor start a thread about it and what was required to get started tuning your rig with it. The learning curve for modeling suspensions is steep. When people hear terms like "second order response" or "frequency domain" eyes start to glaze over. No one needs to be a system response expert to tune suspension, but the theory is intimidating and when you start reading about it either people don't fully understand it or they understand it really well and their explanations aren't accessible to most people.

The program only seems to be mentioned in a handful of Pirate threads, and non really explain how to use it. It doesn't cost that much relative to what people spend on coil overs and springs and could save many hours wasted tuning shocks and attempting to asses the changes.
__________________
-Tony
ajm8127 is offline   Reply With Quote Quick reply to this message
Old 12-15-2019, 11:28 AM   #25 (permalink)
Registered User
 
Join Date: May 2008
Member # 113388
Posts: 265
AJM8127 Thank for the correction and thank you for that excellent explanation. Much better than I could have done!

The program is a very steep learning curve, it also takes a lot of patients. I think I played with this program for 2 years before I got it to work. If you miss one measurement, or it is incorrect the program crashes and it does not highlight the problem area.

It is for that reason that I wanted reevaluate spring selection for single coil overs. A guy should be able to look at a valving chart and get his suspension in the ball park, but he is screwed from the start if the springs he picked wont allow it.

Shim Restackor isn't my program, so I feel weird talking about something I hardly have a grip on. Maybe Ill reach out to the owner.

Going back to spring selection for non bypass set ups. I'm thinking we should suggest three options:

1) No step up rate and and zero preload. This would give you the most plush and accurate feel.

2) 150% step up or less. This is a compromise on response but it is still in the acceptable range. The benefit is more bottoming control at slow shaft speeds.

3) Fully collapsed tender at ride height. I think this might work for some, but I have no experience with it. I am thinking this would be a better slow speed set up? Someone please chime in if they have experience.

Last edited by weswes01; 12-15-2019 at 11:31 AM.
weswes01 is offline   Reply With Quote Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Pirate4x4.Com : 4x4 and Off-Road Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.

** A VERIFICATION EMAIL IS SENT TO THIS ADDRESS TO COMPLETE REGISTRATION!! **

Email Address:
Insurance
Please select your insurance company (Optional)

Log-in


Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 06:24 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Search Engine Optimization by vBSEO 3.6.0 ©2011, Crawlability, Inc.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.