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29-05.-2003, 06:30 AM
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#1 |
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Shimmy
This is a multi-part message in MIME format.
------=_NextPart_000_000C_01C32522.FB81A800 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable When going fairly fast front wheel shimmies (wheel turns a bit left and = right fast back and forth) when taking hands off handlebars. May be = dangerous at speed. What causes it and how can it be fixed (other than = not taking hands off ;-) )? Thanks! --=20 Steve Juniper (snijuniperremovethis@attbi.com) "Invading Iraq to get rid of Saddam Hussein is like using a hand grenade = in a crowded schoolyard to get rid of a bully." ------=_NextPart_000_000C_01C32522.FB81A800 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Diso-8859-1"> <META content=3D"MSHTML 6.00.2800.1170" name=3DGENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=3D#ffffff> <DIV>When going fairly fast front wheel shimmies (wheel turns a bit left = and=20 right fast back and forth) when taking hands off handlebars. May be = dangerous at=20 speed. What causes it and how can it be fixed (other than not taking = hands off=20 ;-) )?</DIV> <DV>Thanks!<BR>-- <BR>Steve Juniper (<A=20 href=3D"mailto:snijuniperremovethis@attbi.com">snijuniperremovethis@attbi= .com</A>)</DIV> <DVI> </DIV> <DVII>"Invading Iraq to get rid of Saddam Hussein is like using a hand = grenade in=20 a crowded schoolyard to get rid of a bully."<BR></DIV></BODY></HTML> ------=_NextPart_000_000C_01C32522.FB81A800-- |
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29-05.-2003, 07:00 AM
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#2 |
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Re: Shimmy
> Steve Juniper wrote:
> > When going fairly fast front wheel shimmies (wheel turns a bit left and right fast back and forth) > when taking hands off handlebars. May be dangerous at speed. What causes it and how can it be > fixed (other than not taking hands off ;-) )? Thanks! > -- > Steve Juniper (snijuniperremovethis@attbi.com) First, please turn of the HTML. It is inappropriate for USENET. Second, an answer to this question can be found in the FAQ http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html |
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29-05.-2003, 07:00 AM
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#3 |
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Guest
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Re: Shimmy
Steve Juniper writes:
> When going fairly fast front wheel shimmies (wheel turns a bit left and right fast back and forth) > when taking hands off handlebars. May be dangerous at speed. What causes it and how can it be > fixed (other than not taking hands off. http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html Jobst Brandt jobst.brandt@stanfordalumni.org Palo Alto CA |
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29-05.-2003, 08:00 AM
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#4 |
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Re: Shimmy
Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, an out
of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or wheels), even a lopsided tire, etc. And/or any combination of the above. Check these things, or have them checked, and corrected, where necessary. May you have the wind at your back. And a really low gear for the hills! Chris Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner |
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29-05.-2003, 08:30 AM
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#5 |
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Guest
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Re: Shimmy
> Many things can cause shimmy. Frame alignment (mis-alignment, actually),
You had it right the first time, in a peculiar sort of way. A frame that's perfectly aligned is more likely to shimmy than one that's out of whack. The bike, by itself, desires to turn only in one direction. You're constantly applying force to make it go straight, and damping out its desire to shimmy. Much easier to create a shimmy in a system where the bike wants to turn in either direction with little effort. I'm sure Jobst can put it more accurately than that, but he probably won't be as nice. --Mike-- Chain Reaction Bicycles www.ChainReaction.com "Chris Zacho "The Wheelman"" <ChriszCorner@webtv.net> wrote in message news:7482-3ED5371E-33@storefull-2353.public.lawson.webtv.net... > Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, an > out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or wheels), > even a lopsided tire, etc. And/or any combination of the above. > > Check these things, or have them checked, and corrected, where necessary. > > May you have the wind at your back. And a really low gear for the hills! Chris > > Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner |
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29-05.-2003, 12:00 PM
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#6 |
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Re: Shimmy
On Wed, 28 May 2003 18:24:30 -0400, Chris Zacho "The Wheelman" wrote:
> Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, an > out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or wheels), > even a lopsided tire, etc. And/or any combination of the above. This is a collection of myths. Fact is a properly aligned frame is more likely to shimmy than a misaligned frame. What would be "poor" frame material? I had a classic lugged steel frame that would shimmy on any fast downhill for me, which I*replaced with a lighter, but otherwise (so I know now) inferior aluminum frame which had 0 shimmy at any speed I could manage. Out of true wheels do not cause shimmy; any oscillations they would cause would be at a much higher frequency than shimmy usually takes. Panniers might, actually, be relevant, but only because they change the overall system response. Loose bearings are often cited as a cause, but there is no mechanism for them to be involved. Read the FAQ that Jobst mentioned. Although my experience was with my hands on the bars only, the shimmy I had was pretty predictable. The myths persist here because anything you might do will change the system resonance enough to maybe change the speed at which shimmy would occur; often to a speed you cannot reach. Shimmy is a systemic response to the bike+rider as a whole. The quickest and cheapest cure is to unload the saddle. It really works. -- David L. Johnson __o | As far as the laws of mathematics refer to reality, they are not _`\(,_ | certain, and as far as they are certain, they do not refer to (_)/ (_) | reality. -- Albert Einstein |
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29-05.-2003, 09:30 PM
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#7 |
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Re: Shimmy
On Wed, 28 May 2003 21:59:41 -0400, "David L. Johnson" <david.johnson@lehigh.edu> wrote:
>On Wed, 28 May 2003 18:24:30 -0400, Chris Zacho "The Wheelman" wrote: > >> Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, an >> out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or wheels), >> even a lopsided tire, etc. And/or any combination of the above. > >This is a collection of myths. Fact is a properly aligned frame is more likely to shimmy than a >misaligned frame. What would be "poor" frame material? I had a classic lugged steel frame that >would shimmy on any fast downhill for me, which I*replaced with a lighter, but otherwise (so I know >now) inferior aluminum frame which had 0 shimmy at any speed I could manage. Out of true wheels do >not cause shimmy; any oscillations they would cause would be at a much higher frequency than shimmy >usually takes. Panniers might, actually, be relevant, but only because they change the overall >system response. Loose bearings are often cited as a cause, but there is no mechanism for them to >be involved. > >Read the FAQ that Jobst mentioned. Although my experience was with my hands on the bars only, the >shimmy I had was pretty predictable. The myths persist here because anything you might do will >change the system resonance enough to maybe change the speed at which shimmy would occur; often to >a speed you cannot reach. > >Shimmy is a systemic response to the bike+rider as a whole. The quickest and cheapest cure is to >unload the saddle. It really works. a poorly made front wheel that is out of 'dish' will give a wicked speed wobble in the truest of frames - Ъ |
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30-05.-2003, 07:30 AM
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#8 |
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Re: Shimmy
On Thu, 29 May 2003 07:43:31 -0400, dax <audaxrex@hotmail.com> wrote:
>a poorly made front wheel that is out of 'dish' will give a wicked speed wobble in the truest of >frames - Ðª× Try having the axle of *just* not quite seated properly on one side. Urgh. Jasper |
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30-05.-2003, 12:00 PM
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#9 |
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Re: Shimmy
dax wrote:
> On Wed, 28 May 2003 21:59:41 -0400, "David L. Johnson" <david.johnson@lehigh.edu> wrote: > > >>On Wed, 28 May 2003 18:24:30 -0400, Chris Zacho "The Wheelman" wrote: >> >> >>>Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, an >>>out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or wheels), >>>even a lopsided tire, etc. And/or any combination of the above. >> >>This is a collection of myths. Fact is a properly aligned frame is more likely to shimmy than a >>misaligned frame. What would be "poor" frame material? I had a classic lugged steel frame that >>would shimmy on any fast downhill for me, which I replaced with a lighter, but otherwise (so I >>know now) inferior aluminum frame which had 0 shimmy at any speed I could manage. Out of true >>wheels do not cause shimmy; any oscillations they would cause would be at a much higher frequency >>than shimmy usually takes. Panniers might, actually, be relevant, but only because they change the >>overall system response. Loose bearings are often cited as a cause, but there is no mechanism for >>them to be involved. >> >>Read the FAQ that Jobst mentioned. Although my experience was with my hands on the bars only, the >>shimmy I had was pretty predictable. The myths persist here because anything you might do will >>change the system resonance enough to maybe change the speed at which shimmy would occur; often to >>a speed you cannot reach. >> >>Shimmy is a systemic response to the bike+rider as a whole. The quickest and cheapest cure is to >>unload the saddle. It really works. > > > a poorly made front wheel that is out of 'dish' will give a wicked speed wobble in the truest of > frames - Ъ Hogwash. Mark McMaster MMcMstr@ix.netcom.com |
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30-05.-2003, 12:00 PM
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#10 |
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Guest
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Re: Shimmy
On Thu, 29 May 2003 22:24:28 -0400, Mark McMaster <MMcMstr@ix.netcom.com> wrote:
>dax wrote: >> On Wed, 28 May 2003 21:59:41 -0400, "David L. Johnson" <david.johnson@lehigh.edu> wrote: >> >> >>>On Wed, 28 May 2003 18:24:30 -0400, Chris Zacho "The Wheelman" wrote: >>> >>> >>>>Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, an >>>>out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or >>>>wheels), even a lopsided tire, etc. And/or any combination of the above. >>> >>>This is a collection of myths. Fact is a properly aligned frame is more likely to shimmy than a >>>misaligned frame. What would be "poor" frame material? I had a classic lugged steel frame that >>>would shimmy on any fast downhill for me, which I replaced with a lighter, but otherwise (so I >>>know now) inferior aluminum frame which had 0 shimmy at any speed I could manage. Out of true >>>wheels do not cause shimmy; any oscillations they would cause would be at a much higher frequency >>>than shimmy usually takes. Panniers might, actually, be relevant, but only because they change >>>the overall system response. Loose bearings are often cited as a cause, but there is no mechanism >>>for them to be involved. >>> >>>Read the FAQ that Jobst mentioned. Although my experience was with my hands on the bars only, the >>>shimmy I had was pretty predictable. The myths persist here because anything you might do will >>>change the system resonance enough to maybe change the speed at which shimmy would occur; often >>>to a speed you cannot reach. >>> >>>Shimmy is a systemic response to the bike+rider as a whole. The quickest and cheapest cure is to >>>unload the saddle. It really works. >> >> >> a poorly made front wheel that is out of 'dish' will give a wicked speed wobble in the truest of >> frames - Ъ > >Hogwash. > > >Mark McMaster MMcMstr@ix.netcom.com I speak from experience, Mark - Ъ |
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30-05.-2003, 09:00 PM
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#11 |
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Re: Shimmy
dax wrote:
> On Thu, 29 May 2003 22:24:28 -0400, Mark McMaster <MMcMstr@ix.netcom.com> wrote: > > >>dax wrote: >> >>>On Wed, 28 May 2003 21:59:41 -0400, "David L. Johnson" <david.johnson@lehigh.edu> wrote: >>> >>> >>> >>>>On Wed, 28 May 2003 18:24:30 -0400, Chris Zacho "The Wheelman" wrote: >>>> >>>> >>>> >>>>>Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, >>>>>an out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or >>>>>wheels), even a lopsided tire, etc. And/or any combination of the above. >>>> >>>>This is a collection of myths. Fact is a properly aligned frame is more likely to shimmy than a >>>>misaligned frame. What would be "poor" frame material? I had a classic lugged steel frame that >>>>would shimmy on any fast downhill for me, which I replaced with a lighter, but otherwise (so I >>>>know now) inferior aluminum frame which had 0 shimmy at any speed I could manage. Out of true >>>>wheels do not cause shimmy; any oscillations they would cause would be at a much higher >>>>frequency than shimmy usually takes. Panniers might, actually, be relevant, but only because >>>>they change the overall system response. Loose bearings are often cited as a cause, but there is >>>>no mechanism for them to be involved. >>>> >>>>Read the FAQ that Jobst mentioned. Although my experience was with my hands on the bars only, >>>>the shimmy I had was pretty predictable. The myths persist here because anything you might do >>>>will change the system resonance enough to maybe change the speed at which shimmy would occur; >>>>often to a speed you cannot reach. >>>> >>>>Shimmy is a systemic response to the bike+rider as a whole. The quickest and cheapest cure is to >>>>unload the saddle. It really works. >>> >>> >>>a poorly made front wheel that is out of 'dish' will give a wicked speed wobble in the truest of >>>frames - Ъ >> >>Hogwash. >> >> >>Mark McMaster MMcMstr@ix.netcom.com > > > I speak from experience, Mark - Ъ So do I. Mark McMaster MMcMstr@ix.netcom.com |
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30-05.-2003, 09:30 PM
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#12 |
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Re: Shimmy
On Fri, 30 May 2003 07:28:18 -0400, Mark McMaster <MMcMstr@ix.netcom.com> wrote:
>dax wrote: >> On Thu, 29 May 2003 22:24:28 -0400, Mark McMaster <MMcMstr@ix.netcom.com> wrote: >> >> >>>dax wrote: >>> >>>>On Wed, 28 May 2003 21:59:41 -0400, "David L. Johnson" <david.johnson@lehigh.edu> wrote: >>>> >>>> >>>> >>>>>On Wed, 28 May 2003 18:24:30 -0400, Chris Zacho "The Wheelman" wrote: >>>>> >>>>> >>>>> >>>>>>Many things can cause shimmy. Frame alignment (mis-alignment, actually), poor frame material, >>>>>>an out of true wheel, Badly loaded panniers (if touring), loose bearings (either headset or >>>>>>wheels), even a lopsided tire, etc. And/or any combination of the above. >>>>> >>>>>This is a collection of myths. Fact is a properly aligned frame is more likely to shimmy than a >>>>>misaligned frame. What would be "poor" frame material? I had a classic lugged steel frame that >>>>>would shimmy on any fast downhill for me, which I replaced with a lighter, but otherwise (so I >>>>>know now) inferior aluminum frame which had 0 shimmy at any speed I could manage. Out of true >>>>>wheels do not cause shimmy; any oscillations they would cause would be at a much higher >>>>>frequency than shimmy usually takes. Panniers might, actually, be relevant, but only because >>>>>they change the overall system response. Loose bearings are often cited as a cause, but there >>>>>is no mechanism for them to be involved. >>>>> >>>>>Read the FAQ that Jobst mentioned. Although my experience was with my hands on the bars only, >>>>>the shimmy I had was pretty predictable. The myths persist here because anything you might do >>>>>will change the system resonance enough to maybe change the speed at which shimmy would occur; >>>>>often to a speed you cannot reach. >>>>> >>>>>Shimmy is a systemic response to the bike+rider as a whole. The quickest and cheapest cure is >>>>>to unload the saddle. It really works. >>>> >>>> >>>>a poorly made front wheel that is out of 'dish' will give a wicked speed wobble in the truest of >>>>frames - Ъ >>> >>>Hogwash. >>> >>> >>>Mark McMaster MMcMstr@ix.netcom.com >> >> >> I speak from experience, Mark - Ъ > >So do I. > >Mark McMaster MMcMstr@ix.netcom.com > > have i got this straight? you took a front wheel, checked to make sure it was out of dish, put it in a frame and fork you knew to be straight, took it up to a good speed - and had no problems? Think about it - if the front wheel is not tracking in the same line as the rear, it will try to pull so that it DOES track - yanking the fork over. Then the rear wheel goes back to where the frame wants it to track - and the front wheel tries to follow THAT - but then the rear... you see what I mean? SHIMMY SHIMMY SHAKE SHAKE. Ъ |
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30-05.-2003, 10:30 PM
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#13 |
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Re: Shimmy
audaxrex snipes anonymously (in new English, no less):
> have i got this straight? you took a front wheel, checked to make sure it was out of dish, put it > in a frame and fork you knew to be straight, took it up to a good speed - and had no problems? > Think about it - if the front wheel is not tracking in the same line as the rear, it will try to > pull so that it DOES track - yanking the fork over. Then the rear wheel goes back to where the > frame wants it to track - and the front wheel tries to follow THAT - but then the rear... you see > what I mean? SHIMMY SHIMMY SHAKE SHAKE. Ъ On bicycles that double track (leave two separate wet tracks after riding through a puddle) I found no propensity to shimmy. The same goes for a front or rear wheel with a broken spoke (substantially out of alignment). From what you say, and how you say it, I take it you are hypothesizing about all this; common fare for wreck.bike. "Think about it!" Jobst Brandt jobst.brandt@stanfordalumni.org Palo Alto CA |
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31-05.-2003, 12:30 AM
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#14 |
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Guest
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Re: Shimmy
On Fri, 30 May 2003 12:58:40 GMT, jobst.brandt@stanfordalumni.org wrote:
>audaxrex snipes anonymously (in new English, no less): > >> have i got this straight? you took a front wheel, checked to make sure it was out of dish, put it >> in a frame and fork you knew to be straight, took it up to a good speed - and had no problems? >> Think about it - if the front wheel is not tracking in the same line as the rear, it will try to >> pull so that it DOES track - yanking the fork over. Then the rear wheel goes back to where the >> frame wants it to track - and the front wheel tries to follow THAT - but then the rear... you see >> what I mean? SHIMMY SHIMMY SHAKE SHAKE. Ъ > >On bicycles that double track (leave two separate wet tracks after riding through a puddle) I found >no propensity to shimmy. The same goes for a front or rear wheel with a broken spoke (substantially >out of alignment). From what you say, and how you say it, I take it you are hypothesizing about all >this; common fare for wreck.bike. > >"Think about it!" > >Jobst Brandt jobst.brandt@stanfordalumni.org Palo Alto CA on my old Louison Bobet, I encountered a wicked speed-shimmy after installing a 'new' rebuilt wheel... i suffered with this for most of the summer till i put a dishing tool on the wheel, discovered the problem, corrected it - and the problem vanished and never returned. I also know from fixing flats on motorcycles - returning a rear wheel to the bike, it is CRITICAL that the rear wheel be centered, or it's speed-shimmy city. Now that's a REAR, and a MOTORCYCLE, but there is some relation, i should think. I am not a physicist, but i think having two well-aligned gyroscopes operating in the same planes but different tracks is gonna cause different harmonics than a simply out-of-true wheel. When someone moves them into different planes by 'correcting' the out-of-dish wheel between the brake shoes, a DIFFERENT set of harmonics should appear - i think. Again, two gyroscope, this time on different axes. Anyway, I'm gonna do some formal experiments with this and will report back - Ъ |
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