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  1. #1
    Senior Member
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    A couple of unimportant questions.

    Hi All, This morning I was readjusting the headset on my '89 Cannondale crit bike (no idea why it's loosened up) and the Vuelta was on the tube. While piddling with the bike my attention centered on the front forks of those on TV. I guess there's a good reason for them to have no offset, but I prefer the gracefull offset on my bike's fork, and in it's day was a pretty serious race bike.

    My questions are a) Why no offset anymore? and b) Just for my own piece of mind, what is the term for the reason that one BB nut and one crankarm pedal are reverse threaded... I know the term, but just can't remember.

    TIA,
    Brad

  2. #2
    working on progress treebound's Avatar
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    The rotation of the ball bearings apply force to the outside circumference (sp?), the reverse threading is so the theoretical force applied by the bearing friction applies a tightening effect to the threaded assembly, or words to that effect.
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  3. #3
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Straight forks have their offset at the crown and not in the fork blades... damn you Colnago.

  4. #4
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    Quote Originally Posted by treebound View Post
    The rotation of the ball bearings apply force to the outside circumference (sp?), the reverse threading is so the theoretical force applied by the bearing friction applies a tightening effect to the threaded assembly, or words to that effect.
    Yeah, but there's a name or term for this physical effect that I just..can't ..remember.

    Brad

  5. #5
    aka: Dr. Cannondale rccardr's Avatar
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    there's a name or term for this physical effect that I just..can't ..remember
    Antirotational Splinkoplocity
    Hard at work in the Secret Underground Laboratory...

  6. #6
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    Quote Originally Posted by bradtx View Post
    Yeah, but there's a name or term for this physical effect that I just..can't ..remember.

    Brad
    I think the word you're looking for is precession. Explanations of this are very difficult but my impression is that the one given above misses the mark a bit. Essentially, at least for the pedals, the bending effect in association with the rotation actually causes the pedal to unscrew in the direction opposite to what would logically be caused by the turning alone.

  7. #7
    working on progress treebound's Avatar
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    I think the bending effect adds to the friction factors involved, it also can lead to thread failures and gouged legs.
    Last edited by treebound; 09-02-11 at 11:19 AM. Reason: redundency, which is probably spelled wrong
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  8. #8
    Cisalpinist Italuminium's Avatar
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    Quote Originally Posted by Sixty Fiver View Post
    Straight forks have their offset at the crown and not in the fork blades... damn you Colnago.
    I think these colnago's with straight fork (chrome) represent the high water mark for steel racing bikes to me. I know there's a lot of negative sentiment against them here at BFC&V, but I just lust after them.
    Pass the Dutchie on the non-drive side.
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  9. #9
    slow as I ever was Ex Pres's Avatar
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  10. #10
    What??? Only 2 wheels? jimmuller's Avatar
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    I believe the word you are looking for is precession.


    This is C&V - my fork is supposed to be bent like that!
    Real cyclists use toe clips.
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  11. #11
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    Quote Originally Posted by DrJim View Post
    I think the word you're looking for is precession. Explanations of this are very difficult but my impression is that the one given above misses the mark a bit. Essentially, at least for the pedals, the bending effect in association with the rotation actually causes the pedal to unscrew in the direction opposite to what would logically be caused by the turning alone.
    I might add that if you want to demonstrate this precession, insert a stick like a dowel or a round pencil in a hole slightly larger than its diameter, grab the end of the stick and rotate it in a circle. Notice what direction the stick tends to rotate.

  12. #12
    slow as I ever was Ex Pres's Avatar
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    Quote Originally Posted by Ex Pres View Post
    Quote Originally Posted by jimmuller View Post
    I believe the word you are looking for is precession.
    Quote Originally Posted by DrJim View Post
    I might add that if you want to demonstrate this precession
    Now something's not quite right about this. I'm Jim (Carter), then we had Jim (Muller), followed by DrJim.
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  13. #13
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    Quote Originally Posted by Ex Pres View Post
    Now something's not quite right about this. I'm Jim (Carter), then we had Jim (Muller), followed by DrJim.
    Ah, yes, the brotherhood of Jim's. Somehow I'm not surprised by this at all.

  14. #14
    working on progress treebound's Avatar
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    Must be a Jim dandy of an answer then.
    (ducking and running lest they jimmy open the doors here and chase me down)
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  15. #15
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    I don't see this as "precession". This is a designer using the residual frictional forces from the bearings in a way that does not contribute to loosening the threaded assembly.

  16. #16
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    Quote Originally Posted by Mike Mills View Post
    I don't see this as "precession". This is a designer using the residual frictional forces from the bearings in a way that does not contribute to loosening the threaded assembly.
    I'm not sure what you mean but we Jim's know that, at least for pedals, it's precession.

  17. #17
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    Quote Originally Posted by Mike Mills View Post
    I don't see this as "precession". This is a designer using the residual frictional forces from the bearings in a way that does not contribute to loosening the threaded assembly.
    Check this out. Need we Jim's say more?

    http://www.sheldonbrown.com/gloss_p.html

  18. #18
    working on progress treebound's Avatar
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    Possibly so, but us Mikes know stuff as well.
    I'm not an engineer, but I am a designer.

    http://www.sheldonbrown.com/brandt/left.html

    edited to add the Jobst Brandt link because he yelled at me online once for misquoting something out of his wheel building book. It may not have been actual yelling per se, but it was somewhat stern and corrective to my understanding.
    Last edited by treebound; 09-02-11 at 12:47 PM.
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  19. #19
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    Quote Originally Posted by treebound View Post
    Possibly so, but us Mikes know stuff as well.
    I'm not an engineer, but I am a designer.
    Well, now we're in what we engineers call a "pissin contest".

  20. #20
    slow as I ever was Ex Pres's Avatar
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    Ich bin ein Engineer, too, although I haven't been employed in that field since '83.

  21. #21
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    Quote Originally Posted by treebound View Post
    Possibly so, but us Mikes know stuff as well.
    I'm not an engineer, but I am a designer.

    http://www.sheldonbrown.com/brandt/left.html

    edited to add the Jobst Brandt link because he yelled at me online once for misquoting something out of his wheel building book. It may not have been actual yelling per se, but it was somewhat stern and corrective to my understanding.
    My "pissin contest" reply was added before your edit. Perhaps we are neering agreement?

  22. #22
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    Quote Originally Posted by DrJim View Post
    My "pissin contest" reply was added before your edit. Perhaps we are neering agreement?
    Some of us old retired engineers can't spell. I meant "nearing".

  23. #23
    Cottered Crank Amesja's Avatar
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    Everyone is named Jim these days. That's why I go by James now -or even amesja (ultra-pig latin anyone?) I worked at a place that had about 30 employees and we have FIVE Jims. Come on parents, can't you think of more original names? I am really sick of being a hyphenated Jim with the initial for my last name.

    Jim, Big Jim, Little Jim, Bigger-than-little-Jim-but-smaller-than-big-Jim-Jim...
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  24. #24
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    Quote Originally Posted by Amesja View Post
    Everyone is named Jim these days. That's why I go by James now -or even amesja (ultra-pig latin anyone?) I worked at a place that had about 30 employees and we have FIVE Jims. Come on parents, can't you think of more original names? I am really sick of being a hyphenated Jim with the initial for my last name.

    Jim, Big Jim, Little Jim, Bigger-than-little-Jim-but-smaller-than-big-Jim-Jim...
    In my case, I never liked James because I thought it is too formal. The Drjim is actually a shortened version of Dr Jimmy which they called me at my first work place many years ago. Something to do with my personality, I think.

  25. #25
    Cottered Crank Amesja's Avatar
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    I'm just the opposite. I never really preferred James over Jim until the last few years, but I have ALWAYS hated Jimmy. It always has seemed like such a pejorative to me. I have a few cousins who insist on calling me that and it always annoys the heck out of me
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