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Old 09-02-11, 10:02 AM   #1
bradtx
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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.

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Old 09-02-11, 10:17 AM   #2
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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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Old 09-02-11, 10:25 AM   #3
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Straight forks have their offset at the crown and not in the fork blades... damn you Colnago.
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Old 09-02-11, 10:46 AM   #4
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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.
Yeah, but there's a name or term for this physical effect that I just..can't ..remember.

Brad
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Old 09-02-11, 10:55 AM   #5
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there's a name or term for this physical effect that I just..can't ..remember
Antirotational Splinkoplocity
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Old 09-02-11, 10:56 AM   #6
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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.
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Old 09-02-11, 11:18 AM   #7
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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.
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Last edited by treebound; 09-02-11 at 11:19 AM. Reason: redundency, which is probably spelled wrong
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Old 09-02-11, 11:40 AM   #8
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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.
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Old 09-02-11, 11:46 AM   #9
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precession
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Old 09-02-11, 11:48 AM   #10
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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!
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Old 09-02-11, 11:51 AM   #11
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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.
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Old 09-02-11, 11:56 AM   #12
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I believe the word you are looking for is precession.
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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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Old 09-02-11, 12:07 PM   #13
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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.
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Old 09-02-11, 12:15 PM   #14
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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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Old 09-02-11, 12:24 PM   #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.
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Old 09-02-11, 12:29 PM   #16
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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.
I'm not sure what you mean but we Jim's know that, at least for pedals, it's precession.
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Old 09-02-11, 12:40 PM   #17
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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.
Check this out. Need we Jim's say more?

http://www.sheldonbrown.com/gloss_p.html
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Old 09-02-11, 12:43 PM   #18
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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.
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Old 09-02-11, 12:48 PM   #19
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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".
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Old 09-02-11, 12:53 PM   #20
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Ich bin ein Engineer, too, although I haven't been employed in that field since '83.
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Old 09-02-11, 12:54 PM   #21
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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.
My "pissin contest" reply was added before your edit. Perhaps we are neering agreement?
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Old 09-02-11, 01:01 PM   #22
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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".
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Old 09-02-11, 01:42 PM   #23
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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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Old 09-02-11, 02:14 PM   #24
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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...
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.
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Old 09-02-11, 02:27 PM   #25
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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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