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Bicycle Shock Absorber Question

  1. Oct 24, 2008 #1
    I have a mountain bicycle with a rear spring shock absorber. Recently the shock absorber broke. Until I can purcahse a replacement I was thinking of building a rigid piece of steel to replace the shock, essentially making my bike a non-suspended unit, but still be able to ride it.

    So here is my question. Do I need to worry about damaging the frame's shock mounting locations? I realize the shock absorber absorbs energy transfered to it in the form of heat energy, but does that mean the mounting locations actually see less force than they would if I mounted the rigid piece of steel?

    It does not seem like it would matter. The force is instantly applied to the mounting locations right? Or does the wasted heat energy actually reduce the force? With the shock, it is a much "softer" ride, but I don't know if that means less force on the mounting points.

    In the end, this would be a fun experiment to try, but I don't want to damage the bike's shock mounting locations.

    Last edited: Oct 24, 2008
  2. jcsd
  3. Oct 24, 2008 #2
    Nobody can help with this?

  4. Oct 24, 2008 #3
    Replacing the spring/shock absorber with a rigid rod will increase the force applied to the mounting locations. This may be acceptable, or you may see cracks develop in this area (probably where the mounting flanges are brazed to the frame). Its hard to be more definite without having a better picture in my mind of what the setup really looks like.
  5. Oct 24, 2008 #4
    Like stated above, replacing the shock absorber with a rigid structure will increase the force placed on the frame. But will this force damage frame, who knows? You haven't provided us with enough information to determine that.
  6. Oct 24, 2008 #5


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    Much more information is indeed needed, but my gut feeling is that you should have no trouble as long as you ride it gently. If you just use it as transportation, rather than going crazy off-road, it should be fine.
  7. Oct 25, 2008 #6
    Well, if you broke your rear shock absorber through use, you likely exceeded it's limit with your love of mountain biking.

    As such, your rigid modification will bend or break the frame under your specific riding conditions.
  8. Oct 25, 2008 #7
    The bike should be OK but I hope you don't do much riding sitting down! Ouch!
  9. Nov 3, 2009 #8
    Hey, does any one happen to know how to find the force that is put on bicycle shock absorber?
    I am a high-school student that is taking physics so if you happen to have the answer please keep it as simple as it can be. Unless it cannot be explained simply, then just give me what you got!
  10. Nov 4, 2009 #9
    Figure out how many g's a bicyclist is asked to do while performing some extreme maneuver. I'm sure someone has figured this out...maybe google it or something.

    This will allow you to figure out the force that the bicyclist puts on the frame (mass of bicyclist * gs * 9.8).

    Then simply draw out the frame on a piece of paper along with its orientation to the ground, and create a free-body diagram. If you don't know how to do that...I don't know, maybe take a side-view picture of the frame and post it here? I can try to do it...
  11. Nov 4, 2009 #10
    So do you mean to take the weight of the bicyclist and the bike and multiply it by the force of gravity 9.8 m/sec²(32 ft/sec²).

    What kind of picture do you need do this?
    I really just need to know the force of a, not so extreme, ride. I was thinking that at the moment I only need what the normal force that would be applied by simply riding around and maybe small jumps. Do you know what i mean?
    Thank you very much!
  12. Nov 4, 2009 #11

    is this the kind of picture that you can use? I can't figure out how to put it on this site.
    This isn't the bike that I will be using, but i am looking to use a bike that has the front forks shocks and the rear shock.
  13. Nov 5, 2009 #12
    Something like this, but representing YOUR bike, as well as the appropriate forces.


    And yeah I understand what you mean by "small bumps". But, if you were for example trying to figure out how strong the frame or the damper needs to be to deal with the forces, you really should look at the most extreme case. And then, you're supposed to design the frame/ damper to be a few times stronger than that, just to be safe.

    Even if you go over small bumps most of the time, that's not a very comforting fact when the frame catastrophically fails on you while going over something slightly more rough...
  14. Nov 5, 2009 #13
    Ok...I dont understand what the picture is. And I understand the face that you say I should be using a more extreme factor.
    Would you say that 10 feet is extreme. I do not ride bikes in a extreme manner.
    Maybe if I explain what I am doing you will be able to give me different advice.
    I am doing an experiment on the strength of magnets and I want to put 2 magnets in a cylinder, with apposing ends facing each other. Then, to demonstrate the strength I am ging to ride the bike and maybe jump a few times,to test the shocks, and I need to know what the,like you said, most force there might be on a shock so that I can figure what size magnet I should use. As a constant I am using 250 pounds, but I do not know the equation to figure out the force that would be put on a Shock.
    By the way I'm Tylar and it's nice to meet you.
    And Thank you very much for your help so far.....
  15. Jun 27, 2011 #14
    To answer the original question (about replacing the shock absorber with a piece of solid steel):

    The answer is easily seen with a "reduction to the absurd" type argument: If you put a really soft spring on your bike, the force at the frame would obviously would be really soft too (, of course until the spring bottomed out, but that's a different story). The solid steel is rather like an infinitely stiff spring. I wouldn't to it, pal.
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