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Calculate clamp force on bike handlebar

  1. Jan 22, 2015 #1
    Hi Folks

    I am looking for some help in a calculation if possible.

    I am looking at a bike design where the handlebars are clamped in place in the stem using only 1 bolt - see the picture attached or link below for an example.

    http://i.ebayimg.com/00/s/MTE5OFgxNjAw/z/rdgAAOxyrYFR2wbP/$(KGrHqF,!k8FHQwpchTzBR2wbP!Now~~60_35.JPG Stem.JPG

    There has been issues with the handle bars slipping forward when in use. I think that this is a manufacturing problem and not a design issue as this type of stem with one bolt is quite common.

    However I would like to prove this mathematically. How do I calculate the force that the bolt and clamp have on the handlebars? I would like to compare a calculation of 1 bolt versus 2 and 4.

    Any help greatly appreciated.

  2. jcsd
  3. Jan 22, 2015 #2

    Quantum Defect

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    I think the problem with this type of goose-neck comes about when the curvature of the sleeve does not match the curvature of the cylinder for the handlebars. If the diameter of the handlebar is undersize, you will be making contact with a very small area on the top and the bottom. As you crank down on the nut, you may be using a lot of force to deform the gooseneck, without making better contact. If the diameter of the handlebar is too large, you will be biting at the edges. I think both cases will allow the handlebar to slip. I have had similar problems with other types of hinged pieces.

    With the handlebar in place, look for gaps. You might try putting some kind of material in between to get a better grip.
  4. Jan 22, 2015 #3
    Cheers for the reply. Yes this is what I think is happening but I am being told it is the design.... so I want to prove with maths that it works so I am looking to calculate the clamping force of 1 bolt versus 2 or 4.
  5. Jan 22, 2015 #4

    Quantum Defect

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    I think that you need to know what the contact area is between goose neck and handlebar. My lovely old road bike has a one-piece gooseneck with a single bolt. The fit between hole and handlebar is pretty snug without any tension on the nut (a lovely fit). With a little tenisoning of the nut, it holds perfect. 30+ years without a problem.

    Not so much the issue of one-nut, two-nuts, etc. but a question of fit, I think.
  6. Jan 23, 2015 #5
    Apologies I only posted that picture as a reference. Please see attached for a picture of the design and relevant dimensions. Both stem head and handle bars are made of stainless steel. I agree that what you are describing is most likely the problem but I need to prove the design first and am looking to find the right equations. Handlebar_Clamp.jpg
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