Results 1 to 5 of 5
  1. #1
    mtbr member
    Reputation:
    Join Date
    May 2011
    Posts
    58

    Coil shock vs air shock, what do their force displacement curves look like?

    What do the force displacement plots actually look like in comparison to one another for your typical rear shocks?

    I've been researching, even been doing a bit of preliminary calculations, i understand a coil will be linear and a air spring is progressive.

    However i've seen some images where air shocks have a greater stiffness for ~ first 5%, then is less tiff than a coil in the middle region, then ramps up at the end of travel.

    It's the initial stiffness region and saggy mid that i don't get, where do they come from? Is this what it's actually like in real world?

    Below is an example of what i'm unclear of-


  2. #2
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,165
    I fixed your graph to try to make it clear to you. Its far from exact as there are many variables when talking air spring curves, but its the general idea.


  3. #3
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,691

  4. #4
    www.derbyrims.com
    Reputation: derby's Avatar
    Join Date
    Jan 2004
    Posts
    6,788
    Quote Originally Posted by DeanFBM View Post
    What do the force displacement plots actually look like in comparison to one another for your typical rear shocks?

    I've been researching, even been doing a bit of preliminary calculations, i understand a coil will be linear and a air spring is progressive.

    However i've seen some images where air shocks have a greater stiffness for ~ first 5%, then is less tiff than a coil in the middle region, then ramps up at the end of travel.

    It's the initial stiffness region and saggy mid that i don't get, where do they come from? Is this what it's actually like in real world?...
    Without a well balance negative spring, an air spring has preloaded air pressure to make usable weighted sag and would be stiffer in initial travel than a linear coil spring with no negative spring.

    A negative spring counteracts the preload of the positive compression resisting spring. Also a negative spring resists inertia that could top out harshly from rebound momentum. The negative spring prevents harsh top out, and can prevent full travel to the full extension of mechanical travel.

  5. #5
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,691
    Quote Originally Posted by derby View Post
    Without a well balance negative spring, an air spring has preloaded air pressure to make usable weighted sag and would be stiffer in initial travel than a linear coil spring with no negative spring.

    A negative spring counteracts the preload of the positive compression resisting spring. Also a negative spring resists inertia that could top out harshly from rebound momentum. The negative spring prevents harsh top out, and can prevent full travel to the full extension of mechanical travel.
    This is a minor nit pick, but a negative air spring does make the initial travel "stiffer", based on the technical definition of spring rate. It takes the preloaded initial travel section of the force-displacement curve, and pulls it down slightly. There is less preload, but the curve is steeper, hence stiffer.

    I agree that the negative air does make the initial travel seem less "harsh", maybe because you aren't topping out all the time, or because you aren't overdamped.



Similar Threads

  1. going from air shock to a coil rear shock
    By HowMaybesGo in forum Shocks and Suspension
    Replies: 11
    Last Post: 11-30-2010, 04:38 PM
  2. GT Force Coil Shock
    By Prostreet513 in forum GT
    Replies: 1
    Last Post: 09-27-2010, 06:16 PM
  3. Replies: 1
    Last Post: 08-16-2010, 06:05 PM
  4. Replies: 3
    Last Post: 07-21-2007, 06:10 PM
  5. replacing air shock with coil shock
    By charlielori1168 in forum Shocks and Suspension
    Replies: 1
    Last Post: 11-26-2005, 12:10 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •