Today's Forum Topics
Set as homepage
|
View
New Forum Topics Today's Forum Topics Set as homepage |
 |
|
|||||||
Welcome to CyclingForums.com You are currently viewing our website as a guest which gives you limited access to view most discussions. You will have to register before you can post to this thread. By joining our free online community you will have access to post new topics, communicate privately with other cyclingforums.com members (PM), respond to polls, upload photos and access other special features like product reviews and classifieds. |
|
|
Thread Tools | Search this Thread | Display Modes |
08-07.-2004, 05:30 AM
|
#1 |
|
Guest
Posts: n/a
|
Low speed shimmy?
At 15+ mph with my hands off the bars, violent shimmy will
start within a few seconds. Should I treat it just like the high speed, hands-on shimmy more commonly asked about here? I get no shimmy with my hands on the bar up to 45 mph (don't know beyond that). -- Rick Onanian |
|
|
|
08-07.-2004, 12:30 PM
|
#2 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
in my experience, it happens in harmonics - e.g. one that
happens at 10mph will also be present at 20, but probably not of the same amplitude. just treat it the same. what kind of frame/wheel combo do you have? Rick Onanian wrote: > At 15+ mph with my hands off the bars, violent shimmy will > start within a few seconds. Should I treat it just like > the high speed, hands-on shimmy more commonly asked about > here? I get no shimmy with my hands on the bar up to 45 > mph (don't know beyond that). > -- > Rick Onanian |
|
|
|
08-07.-2004, 09:46 PM
|
#3 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <nospam@example.net>
wrote: >in my experience, it happens in harmonics - e.g. one that >happens at 10mph will also be present at 20, but probably >not of the same amplitude. just treat it the same. Mine happens at any speed above 15. I ride no-hands at a steady speed, and the shimmy increases in amplitude pretty quickly. >what kind of frame/wheel combo do you have? http://members.cox.net/thc69/bikes/tcr2.jpg 20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum compact frame. I believe my answer is actually in my tall stem, according to this parallel thread: http://groups.google.com/groups?&th=4771eb045db5278c I'm not sure how the stem can affect handling when riding no-hands, except maybe in how the weight of the handlebars affects steering. -- Rick Onanian |
|
|
|
09-07.-2004, 12:15 AM
|
#4 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
Rick Onanian wrote:
> Mine happens at any speed above 15. I ride no-hands at a > steady speed, and the shimmy increases in amplitude pretty > quickly. > > http://members.cox.net/thc69/bikes/tcr2.jpg I think I've spotted your problem. You have a chainring in your front spokes. Bill "HTH" S. |
|
|
|
09-07.-2004, 12:15 AM
|
#5 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On Thu, 08 Jul 2004 15:07:06 GMT, "S o r n i"
<sorni@bite-me.san.rr.com> wrote: >> http://members.cox.net/thc69/bikes/tcr2.jpg > >I think I've spotted your problem. > >You have a chainring in your front spokes I've been waiting for that one.  -- Rick Onanian |
|
|
|
09-07.-2004, 01:46 AM
|
#6 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
Rick Onanian <spamsink@cox.net> wrote:
> At 15+ mph with my hands off the bars, violent shimmy will > start within a few seconds. Should I treat it just like > the high speed, hands-on shimmy more commonly asked about > here? I get no shimmy with my hands on the bar up to 45 > mph (don't know beyond that). does it happen with your aerobars removed? otherwise i'm partial to blaming it on that stem ;-) -- david reuteler reuteler@visi.com |
|
|
|
09-07.-2004, 08:01 AM
|
#7 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On 08 Jul 2004 16:41:43 GMT, David Reuteler <reuteler@visi.com>
wrote: >Rick Onanian <spamsink@cox.net> wrote: >> At 15+ mph with my hands off the bars, violent shimmy >> will start > >does it happen with your aerobars removed? otherwise i'm >partial to blaming it on that stem ;-) I'm too lazy to remove the aerobars to find out. I was thinking I'd fool with the headset preload, which may not be perfect. -- Rick Onanian |
|
|
|
09-07.-2004, 10:13 PM
|
#8 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
Rick Onanian wrote:
> On Wed, 07 Jul 2004 20:15:22 -0700, jim beam > <nospam@example.net> wrote: > >>in my experience, it happens in harmonics - e.g. one that >>happens at 10mph will also be present at 20, but probably >>not of the same amplitude. just treat it the same. > > > Mine happens at any speed above 15. I ride no-hands at a > steady speed, and the shimmy increases in amplitude pretty > quickly. > > >>what kind of frame/wheel combo do you have? > > > http://members.cox.net/thc69/bikes/tcr2.jpg > > 20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum > compact frame. I believe my answer is actually in my tall > stem, according to this parallel thread: > http://groups.google.com/groups?&th=4771eb045db5278c > > I'm not sure how the stem can affect handling when riding > no-hands, except maybe in how the weight of the handlebars > affects steering. > -- > Rick Onanian frame & wheel in isolation should be fine. but waht about that rack??? conventional racks are firmly attached to eyelets at the stays, both top & bottom. the bottom clip arrangement you have should be ok, but that top attachment is going to offer no lateral stiffness whatsoever - any lateral movement of the bike is going to have that rack acting like a textbook reciprocating mass. sure, check into the handlebar situation, but i'd address the rack situation first. personally, i commute with a back pack. |
|
|
|
09-07.-2004, 10:46 PM
|
#9 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
Right, jb. Putting a rear rack on a bicycle has caused
a shimmy in my personal experience, thouggh it came on at 30 mph. "jim beam" <nospam@example.net> wrote in message news:0eadnVHhNs29BHPd4p2dnA@comcast.com... > Rick Onanian wrote: > > On Wed, 07 Jul 2004 20:15:22 -0700, jim beam > > <nospam@example.net> wrote: > > > >>in my experience, it happens in harmonics - e.g. one > >>that happens at 10mph will also be present at 20, > >>but probably not of the same amplitude. just treat > >>it the same. > > > > > > Mine happens at any speed above 15. I ride no-hands at a > > steady speed, and the shimmy increases in amplitude > > pretty quickly. > > > > > >>what kind of frame/wheel combo do you have? > > > > > > http://members.cox.net/thc69/bikes/tcr2.jpg > > > > 20mm 110 psi tire on CXP21 rim on 105 hub, Giant > > aluminum compact frame. I believe my answer is actually > > in my tall stem, according to this parallel thread: > > http://groups.google.com/groups?&th=4771eb045db5278c > > > > I'm not sure how the stem can affect handling when > > riding no-hands, except maybe in how the weight of the > > handlebars affects steering. > > -- > > Rick Onanian > > frame & wheel in isolation should be fine. but waht about > that rack??? conventional racks are firmly attached to > eyelets at the stays, both top & bottom. the bottom clip > arrangement you have should be ok, but that top attachment > is going to offer no lateral stiffness whatsoever - any > lateral movement of the bike is going to have that rack > acting like a textbook reciprocating mass. > > sure, check into the handlebar situation, but i'd address > the rack situation first. personally, i commute with a > back pack. |
|
|
|
10-07.-2004, 12:46 AM
|
#10 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <nospam@example.net>
wrote: >> http://groups.google.com/groups?&th=4771eb045db5278c >> >> I'm not sure how the stem can affect handling when riding >> no-hands, except maybe in how the weight of the >> handlebars affects steering. > >frame & wheel in isolation should be fine. but waht about >that rack??? conventional racks are firmly attached to >eyelets at the stays, both top & bottom. the bottom clip >arrangement you have should be ok, but that top attachment >is going to offer no lateral stiffness whatsoever - any >lateral movement of the bike is going to have that rack >acting like a textbook reciprocating mass. Great observation! I would have never considered that something attached to the rear of the bike [seemingly firmly] could cause front-end oddness, but I'll definitely have to look into it. I have a couple extra clamps like the ones on the bottom which I could use at the top too; maybe I'll try them, or some other method for stiffening the rack. -- Rick Onanian |
|
|
|
10-07.-2004, 10:15 PM
|
#11 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
It sure surprised me too, but I found this phenomenom on
several frames, always with alloy racks. My current ride has a steel K-Mart rack, and no shimmy, whether there is any connection, I don't care to suppose. There are many things which can cause shimmys, also see: http://groups.google.com/groups?q=s...=en&lr=&ie=UTF- 8&start=0&sa=N "Rick Onanian" <spamsink@cox.net> wrote in message news:daete05shdgjo641b34ishld3ekindbh8e@4ax.com... > On Fri, 09 Jul 2004 06:09:51 -0700, jim beam > <nospam@example.net> wrote: > >> http://groups.google.com/groups?&th=4771eb045db5278c > >> > >> I'm not sure how the stem can affect handling when > >> riding no-hands, except maybe in how the weight of the > >> handlebars affects steering. > > > >frame & wheel in isolation should be fine. but waht about > >that rack??? conventional racks are firmly attached to > >eyelets at the stays, both top & bottom. the bottom clip > >arrangement you have should be ok, but that top > >attachment is going to offer no lateral stiffness > >whatsoever - any lateral movement of the bike is going to > >have that rack acting like a textbook reciprocating mass. > > Great observation! I would have never considered that > something attached to the rear of the bike [seemingly > firmly] could cause front-end oddness, but I'll definitely > have to look into it. > > I have a couple extra clamps like the ones on the bottom > which I could use at the top too; maybe I'll try them, or > some other method for stiffening the rack. > -- > Rick Onanian |
|
|
|
12-07.-2004, 09:13 AM
|
#12 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
Please......
Get rid of the wheel reflectors.. If you don't think that they are capable of causing your shimmy, spin a suspended wheel with shop air and see what the effect of the reflector weight is at speed. You'll be surprised a how much the fork and bars will jump around even a low rpm.. (15 mph).. I am told by others here that this cannot be the cause of a shimmy, but I found this to be the total problem with an old Trek 750 cross bike that almost threw me into the woods the first time I got it up to 25 MPH on a downgrade. My motorcycle experience with wheel balancing to eliminate the deadly "Speed Wobble" suggests that some attempt at balancing bike wheels is not a wasted effort when dealing with shimmy. Get rid of the reflectors for one ride and let me know please! Bob Flumere rflumere@comcast.net On Thu, 08 Jul 2004 08:36:36 -0400, Rick Onanian <spamsink@cox.net> wrote: >On Wed, 07 Jul 2004 20:15:22 -0700, jim beam ><nospam@example.net> wrote: >>in my experience, it happens in harmonics - e.g. one that >>happens at 10mph will also be present at 20, but probably >>not of the same amplitude. just treat it the same. > >Mine happens at any speed above 15. I ride no-hands at a >steady speed, and the shimmy increases in amplitude >pretty quickly. > >>what kind of frame/wheel combo do you have? > >http://members.cox.net/thc69/bikes/tcr2.jpg > >20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum >compact frame. I believe my answer is actually in my tall >stem, according to this parallel thread: >http://groups.google.com/groups?&th=4771eb045db5278c > >I'm not sure how the stem can affect handling when riding >no-hands, except maybe in how the weight of the handlebars >affects steering. Bob Flumere rflumere@comcast.net |
|
|
|
12-07.-2004, 12:30 PM
|
#13 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On Sun, 11 Jul 2004 23:58:43 GMT, Bob Flumere
<rflumere@comcast.net> wrote: >Please...... > >Get rid of the wheel reflectors.. > >If you don't think that they are capable of causing your >shimmy, spin a suspended wheel with shop air and see what >the effect of the reflector weight is at speed. You'll be >surprised a how much the fork and bars will jump around >even a low rpm.. (15 mph).. > >I am told by others here that this cannot be the cause of a >shimmy, but I found this to be the total problem with an >old Trek 750 cross bike that almost threw me into the woods >the first time I got it up to 25 MPH on a downgrade. > >My motorcycle experience with wheel balancing to eliminate >the deadly "Speed Wobble" suggests that some attempt at >balancing bike wheels is not a wasted effort when dealing >with shimmy. > >Get rid of the reflectors for one ride and let me >know please! > >Bob Flumere rflumere@comcast.net > > > >On Thu, 08 Jul 2004 08:36:36 -0400, Rick Onanian ><spamsink@cox.net> wrote: > >>On Wed, 07 Jul 2004 20:15:22 -0700, jim beam >><nospam@example.net> wrote: >>>in my experience, it happens in harmonics - e.g. one that >>>happens at 10mph will also be present at 20, but probably >>>not of the same amplitude. just treat it the same. >> >>Mine happens at any speed above 15. I ride no-hands at a >>steady speed, and the shimmy increases in amplitude pretty >>quickly. >> >>>what kind of frame/wheel combo do you have? >> >>http://members.cox.net/thc69/bikes/tcr2.jpg >> >>20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum >>compact frame. I believe my answer is actually in my tall >>stem, according to this parallel thread: >>http://groups.google.com/groups?&th=4771eb045db5278c >> >>I'm not sure how the stem can affect handling when riding >>no-hands, except maybe in how the weight of the handlebars >>affects steering. > >Bob Flumere rflumere@comcast.net Dear Bob, Your plea raises an interesting question. It's often been stated here that wheel-balancing is pointless on bicycles because the wheel mass is so small compared to the bike and rider. How heavy would an unbalanced weight on a wheel have to be before wheel-balancing became worthwhile in the eyes of the naysayers? Carl Fogel |
|
|
|
13-07.-2004, 05:54 AM
|
#14 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On Sat, 10 Jul 2004 06:01:51 -0700, "Dale Benjamin"
<daleb@k-online.com> wrote: >It sure surprised me too, but I found this phenomenom on >several frames, always with alloy racks. My current ride >has a steel K-Mart rack, and no shimmy, whether there is >any connection, I don't care to suppose. It is a lightweight alloy rack. Sure enough, it is definitely involved; this weekend, put a trunk on it, with a few pounds of stuff in it, and the shimmy is barely detectable. I also had two full 32oz bottles in the rear bottle cages that hang off the end of the rack. It seems strange to me that the rack would do that when unweighted, and behave when loaded; unweighted, it would seem to not have enough mass to have such an effect. However, who am I to argue with results? >There are many things which can cause shimmys, also see: >http://groups.google.com/groups?q=s...=en&lr=&ie=UTF- >8&start=0&sa=N Yeah, I see in-depth discussions constantly about it, which is why I haven't asked how to troubleshoot it; I just wanted to know if the troubleshooting process is the same, as the shimmy is under different conditions than usually discussed (usually, high speed with hands on the bars). -- Rick Onanian |
|
|
|
13-07.-2004, 06:16 AM
|
#15 |
|
Guest
Posts: n/a
|
Re: Low speed shimmy?
On Sun, 11 Jul 2004 23:58:43 GMT, Bob Flumere <rflumere@comcast.net>
wrote: >Get rid of the wheel reflectors.. If you don't think that >they are capable of causing your shimmy, spin a suspended >wheel with shop air and see what the effect of the >reflector weight is at speed. You'll be surprised a how >much the fork and bars will jump around even a low rpm.. >(15 mph).. I haven't given this attention to the front wheel, but removing the reflectors from my rear wheel does not result in a balanced wheel. I had observed a few months ago that spinning my rear up to a good speed while holding the bike in the air produced quite a strong reciprocation force where I held the bike. In a recent discussion regarding tires, traction, handling, and testing of all three, after I suggested that the force would load and unload the tire a little bit each revolution, resulting in uneven traction, Jobst asserted that it couldn't affect handling, and gave the impression that such a force is so trivial in the grand scheme of things as to have no effect whatsoever in a bicycling context. I am not entirely convinced. It did require a few steel 1/2" nuts taped to the rim before I got it reasonably balanced. >I am told by others here that this cannot be the cause of a >shimmy, but I found this to be the total problem with an >old Trek 750 cross bike that almost threw me into the woods >the first time I got it up to 25 MPH on a downgrade. I'm not sure how vertical forces could cause a horizontal/rotational shimmy, but I also wasn't sure how a rear rack could cause front shimmy -- when in fact, weighting my rear rack with some extra tools, a couple apples, and a single-serving applesauce, as well as two water bottles, almost entirely eliminated the shimmy. Actually, while typing that bit above, I realized another major difference. In the shimmy-prone rides, I'm pretty sure I only had one bottle in the rack's bottle cages. In the shimmy-free ride on Saturday, I had bottles in both cages. Maybe I need to bring two half-full bottles instead of one full bottle. >My motorcycle experience with wheel balancing to eliminate >the deadly "Speed Wobble" suggests that some attempt at >balancing bike wheels is not a wasted effort when dealing >with shimmy. See, mine is not a "speed" wobble, it's more of a "slow" wobble, and only with no hands. As such, I was just wondering if the troubleshooting process is the same as for hands-on high-speed wobble, for which there exists truckloads of information to be found in the archives of this newsfroup. >Get rid of the reflectors for one ride and let me >know please! I might give it a try, but I think it's something to do with the rear rack. -- Rick Onanian |
|
|
Linear Mode
