Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Mercedes-Benz Performance Paddock

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 03-02-2019, 12:27 PM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
Mercedes spring rate deciphering

Does anyone know what the correct conversion process would be to get a usable spring rate number from the Mercedes books
" Mm of travel per 1000 newtons "
To pounds per inch or kg per mm. I can't find anything and I can't quite wrap my head around how you would go about it since it's a set weight and not distance.

Sent from my SM-J737A using Tapatalk
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #2  
Old 03-03-2019, 08:36 AM
88Black560SL
 
Join Date: Oct 2004
Location: NC
Posts: 2,971
Quote:
Originally Posted by rwd4evr View Post
Does anyone know what the correct conversion process would be to get a usable spring rate number from the Mercedes books
" Mm of travel per 1000 newtons "
To pounds per inch or kg per mm. I can't find anything and I can't quite wrap my head around how you would go about it since it's a set weight and not distance.

Sent from my SM-J737A using Tapatalk
Does the manual actually say mm per Newton.

If it does divide mm/KN by 5710.1

if it says 1000 Newtons per mm travel then multiply KN/mm by 5710.1
__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo
Reply With Quote
  #3  
Old 03-03-2019, 09:24 PM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
Here's a page. I'm not certain off hand what my 78 450slc is though. No epc at the moment.

Sent from my SM-J737A using Tapatalk
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #4  
Old 03-03-2019, 11:09 PM
Registered User
 
Join Date: Feb 2011
Location: Modesto CA
Posts: 2,748
rwd:

Use these #s to do your conversion:
1000N = 225 lb.

225/deflection (in mm) x 25.4 (mm/in) [or, 5715/deflection] = lbs. per inch

Example: 225/21.2 x 25.4 = 269.8 lb/in
Reply With Quote
  #5  
Old 03-03-2019, 11:26 PM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
Awesome. Thank you!! Gotta keep. That formula. I'll never keep. That straight.
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #6  
Old 03-06-2019, 12:38 AM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
So. With your help I've determined the rear spring is 359.43 lbs/inch. The problem I have now is that I have two coils cut off it. So how can I figure that out? Coil count and spring diameter I'll have to check.

Sent from my SM-J737A using Tapatalk
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com

Last edited by rwd4evr; 03-06-2019 at 02:42 PM.
Reply With Quote
  #7  
Old 03-06-2019, 02:01 PM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
348.47 lbs/in front springs.

Sent from my SM-J737A using Tapatalk
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #8  
Old 03-10-2019, 11:56 PM
88Black560SL
 
Join Date: Oct 2004
Location: NC
Posts: 2,971
Quote:
Originally Posted by rwd4evr View Post
So. With your help I've determined the rear spring is 359.43 lbs/inch. The problem I have now is that I have two coils cut off it. So how can I figure that out? Coil count and spring diameter I'll have to check.

Sent from my SM-J737A using Tapatalk
The answer to that problem is a little more complex. The linear portion of the spring stiffness will be inversely proportional to the length. Unfortunately some portion of the part of the spring you cut off is not in the linear portion of the spring in fact ~3/4 of the first coil are against the control or spring saddle and not acting as a spring at all.

The best you can do is get the range of stiffness percent which will be somewhere between the original stiffness and the original stiffness*(original length/cut length). My guess is about 1/2 way in between for the first two coils.
__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo
Reply With Quote
  #9  
Old 03-11-2019, 12:02 AM
88Black560SL
 
Join Date: Oct 2004
Location: NC
Posts: 2,971
Quote:
Originally Posted by rwd4evr View Post
Here's a page. I'm not certain off hand what my 78 450slc is though. No epc at the moment.

Sent from my SM-J737A using Tapatalk
A 450SLC has a very stiff front spring. I use 450SLC springs in my V12 powered 560SL to return the car to stock height due to the increased weight of the engine. The extra 200LB up front of engine and mods dropped the nose about 1" with the stock 560SL springs.
__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo
Reply With Quote
  #10  
Old 03-11-2019, 01:19 AM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
Yeah. I'm working on a 450slc. I've got two coils removed in the front. Spring rate isn't bad but it's a little too low. Iike it where it is but suspension geometry is screwed at this point. Rear is a hair low too. I'm putting adjustable dampers on and I'm stiffening it up more. I need about 800 front 600 rear.
I'm planning on removing a 3rd coil up front and a second in the rear and adding spacers under the spring to get the height back. I'm going to put adjustable perches in the front with proper rated springs(soon I hope) but the rear is a bit tricky to do that with the shock inside. The upper mount doesn't allow for a true coilover without some seriuos hacking either. It's a drift only car at this point and it needs to be way stiffer than it is. Body roll is pretty bad.

The springs in the car are 115 324 2204 and
114 321 0704

Sent from my SM-J737A using Tapatalk
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #11  
Old 03-11-2019, 01:35 AM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
Quote:
Originally Posted by Roncallo View Post
The answer to that problem is a little more complex. The linear portion of the spring stiffness will be inversely proportional to the length. Unfortunately some portion of the part of the spring you cut off is not in the linear portion of the spring in fact ~3/4 of the first coil are against the control or spring saddle and not acting as a spring at all.



The best you can do is get the range of stiffness percent which will be somewhere between the original stiffness and the original stiffness*(original length/cut length). My guess is about 1/2 way in between for the first two coils.
So the actual spring rate would be more accurately figured minus one coil to begin with then determined with the removed coils from there? So the front is 11 coils with a 4" ID. Say one is dead. So 40" of spring. So if I removed 30% of it how does that affect it?

I wish I could go back and tell me to go to school for mechanical engineering. I'm pretty intelligent but under educated. That's the kind of stuff that's a bit harder to teach yourself. I've been learning more and more geometry building this car but the actual engineering aspect, forces and loads.......

Sent from my SM-J737A using Tapatalk
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #12  
Old 03-11-2019, 10:50 PM
88Black560SL
 
Join Date: Oct 2004
Location: NC
Posts: 2,971
Quote:
Originally Posted by rwd4evr View Post
So the actual spring rate would be more accurately figured minus one coil to begin with then determined with the removed coils from there? So the front is 11 coils with a 4" ID. Say one is dead. So 40" of spring. So if I removed 30% of it how does that affect it?

I wish I could go back and tell me to go to school for mechanical engineering. I'm pretty intelligent but under educated. That's the kind of stuff that's a bit harder to teach yourself. I've been learning more and more geometry building this car but the actual engineering aspect, forces and loads.......

Sent from my SM-J737A using Tapatalk
Divide the spring rate of your 40" section buy 0.7. That will give you the new spring rate of your now 28" section.
__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo
Reply With Quote
  #13  
Old 03-12-2019, 12:12 PM
Registered User
 
Join Date: Feb 2011
Location: Modesto CA
Posts: 2,748
Quote:
Originally Posted by rwd4evr View Post
So the actual spring rate would be more accurately figured minus one coil to begin with then determined with the removed coils from there? So the front is 11 coils with a 4" ID. Say one is dead.

If there are 11 coils and 1 is dead, then 10 coils are active.
If 2 coils are removed, then 8 are active.
The active wire length is therefor 80% of the original.
Divide the original spring rate by .8 to calculate the new rate.
Reply With Quote
  #14  
Old 03-12-2019, 04:19 PM
rwd4evr's Avatar
Master hull craftsman
 
Join Date: Apr 2012
Location: delaware
Posts: 587
Quote:
Originally Posted by Roncallo View Post
Divide the spring rate of your 40" section buy 0.7. That will give you the new spring rate of your now 28" section.
Thanks. I figured that could work but I just didn't know if it would be as simple and linear as that.
__________________
WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com
Reply With Quote
  #15  
Old 03-12-2019, 11:13 PM
88Black560SL
 
Join Date: Oct 2004
Location: NC
Posts: 2,971
Quote:
Originally Posted by rwd4evr View Post
Thanks. I figured that could work but I just didn't know if it would be as simple and linear as that.
Its not that linear. Where the dead coils end changes with load. But its as best an estimate as you will get.
__________________
To see my 129 parts for sale visit:
http://stores.ebay.com/The-Mercedes-SL-Store
John Roncallo
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 01:26 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page