Shimmy Anyone?!

[CJH]

Hi!
So I've just built up my new bike two weeks ago and have been able to put in 4 or 5 good rides. It's a Mondonico ELOS lugged steel frame and fork. After some delays in the process of the frame being finished I was really happy with the way everything turned out, the pearl white paint had just the right tone and so on... However on my ride today for some reason I did some "nohanded" riding/coasting and was alarmed to discover a very prominent shimmy developing at speeds from 25mph and up! It happened every time I took my hands off the bars at 25mph and up no matter if I was rolling downhill or coasting on the flats or in slight turn. The shimmy would start as a tiny wobble back and forth and rappidly escalate to the point where I had to grab the bars. I couldn't feel anything out of order going slower than 25mph nohanded or when I had my hands on the bars at greater speed. The frame is brand new custom build, with the following specs:
Seat tube 58 c-c
Top tube 57.5c-c
HTA 74
STA 73.5
Threaded Mondonico steel fork
Reord Group
I should also say that I've gone over every thing I can think of to isolate the problem but to no avail. Headset is smooth not tight nor any play, cable houseing is not restricting of "pushing", wheels are true and the hubs are smooth, tried two different sets of wheels just to make sure (Open Pro Record hubs and Nucleons). I also tried sitting further back or forward on the saddle so as to change the weight distribution to see if that had any effect on the shimmy but there wasn't any! Oh and obviously I haven't crashed or harmed the frame in any other way. I should also say that I have contacted the bike shop I got the frame from and they are going to contact Torelli who is the importer to see if they have any ideas before putting the frame on an alignment table! Torelli makes a big deal about how the frames they deal with are put through the paces and checked for alignment and prepped before assembly so supposedly it should be good but who knows! I did put a stringline from the rear dropouts around the headtube and back and measured distance from line to seat tube and came up with a deviation of 1mm, however I'm not quite sure how scientific that is! In the meantime I thought I'd do some research on my own and what better source than Serotta forum! Any ideas or experiences would be greatly appreciated!

Thanks!

[Kurt]

nice sounding bike - your hta is a little steeper than usual, what is your stem length? What happens if you move up or back on the saddle? Did you try a different set of wheels? Might be a balance or harmonic kind of issue. Maybe frame will wobble given the right chance, but not at 25.

edit: sorry, only read the top part, so you tried diff wheels and saddle, if you clamp your legs on the tt what happens and maybe take it out for a 40mph blast and see how stable it is - I had a bike do that, nothing will scare the crap out of you quicker than a shake - I had to get rid of the frame and get another - I always thought it was because the tt was too long relative to the stem length (59.5/110) bikes like weight over the front.

http://www.spectrum-cycles.com/615.htm
http://www.sheldonbrown.com/brandt/shimmy.html

[Peter]

Try this experiment: have a friend ride the bike at the speed the shimmy occurs. I'm a believer that the rider has influence on the possibility of shimmy, and if it does not occur with a different rider aboard, then it is a mismatch between the rider and the frame. How so? The way your weight is distributed top-to-bottom affects your center of gravity, and that is a factor in shimmy.

Need proof? My daily bike has a rear rack. I usually throw my commuter panniers on it and have no shimmy problems. Once a week I secure a 5lb. mechanic's bag on top of the rack. With the bag on the rack, I can't take both hands off the bars at almost any speed because the front end starts to do the watusi.

So you've checked everything else? I won't belabor you with the typical suggestions, then. As for the string test: I was broadsided by a car a year ago. A string test revealed about a 4mm offset. When placed on an alignment table, the error at the top of the 55cm seat tube was about 25mm!

Keep us informed as I, for one, am interested how Torelli handles your problem.

[CJH]

Kurt and Peter!
Thanks for your responses! I did try clamping the top tube with my knees, shimmy stops, which I'm not at all surprised about but then what?! According to the Spectrum link shimmy relates (partly anyway) torsional flex in the front end and so manly by the top tube being the common week link! If I understood it correctly that is! Have yet to try more speed and see if anything changes. But my concern is that it happens with no hands on bars at 25mph, which is not all that fast. I want to be able to for example remove a jacket, eat a power bar etc. while coast down a hill for instance. Clamping the top tube with my knees just dosen't cut imo. Peter I'll have to get a friend to ride it and see if anything changes, good sugestion! I don't think that I'm being unreasonble wanting a shimmyless frame for $2000+??? As for how Torelli handles this, I guess I'll find out shortly. I should point out though that Torelli and the LBS have been good to deal with reg. some other issues so I'm hoping this will be resolved one way or the other without too much trouble...

Thanks Again!!!

[mdeeds71]

CJH...I don't know your location but is it on the West coast??? If so did you get that bike in Santa Clara...


I know a few people with these Mondonico frames and they bomb down the hills at 40 plus with no shimmy that I have ever heard of...

[CJH]

NO I'm actually on the East Coast. New York City. Funny thing though, the bike feels completely stable when riding hands on the handlebars albeit I haven't taken it above 35mph yet. It's the no-handed riding where things get screwy. But hopefully it'll be resolved, waiting to hear back from my LBS and Torelli!
Thanks!

[shaq-d]

but i'll guess it's because it isn't really "shimmy" when you don't have your hands on the handlebars. that is, it's not considered a problem. if it handles good with your hands on the handlebars, the rest isn't really indicative of anything.

sd

[CJH]

There's actually been some helpful responses, I appreciate that! Could always use more... I think I'd consider the oscilation in the front end to be a shimmy wether or not I have my hands on the bars. Agreed it would be a bit more serious if it was doing this when riding with hands on the bars! However I don't believe I'm the only who would consider a "nohanded" shimmy to be a problem! To me it smells fishy, something ain't right if the bike won't run true no matter what reasonble riding position is adopted?! Thoughts anyone???

[Smiley]

CJH , if your taking you hands off the bars and also moving your center of gravity back ( by getting more up-right ) then you are de-weighting your front wheel . I'd be more concerned about the problem if your hands were on the bars . My question would be about the design of the frame with a truly weighted front end . I know lots of folks here like to test the front ends with Hands off steering . May I ask what the trail of the front end is if you have it , my guess is its low like 5.4 or there about .

[CJH]

Thanks for your response Smiley. I just measured the trail and I came up with 55mm (5.5cm), so given +/-1mm you're right on in your assumption! Now how does that relate to the shimmy?! I've read that the more trail the more stable a bike will be steering wise, but also less responsive. But does it also mean that there is a point in which there is too much trail for highspeed stability or would the bike just not be manuverable above a certain amount of trail and speed? Also wondering do you not see it as a problem that a bike shimmys while rideing nohanded at say 25mph (honestly wondering), I mean I don't want to seem as if I have unrealistic expectations on a bike but isn't it sort of a red flag?! I would also be more alarmed if this happened while on the bars but still 25mph isn't all that fast. I would be more understanding if it occured during 50mph no handed descents, I guess that's maybe cause I won't be doing much of those...
Thanks!

[Orin]

Thanks for your response Smiley. I just measured the trail and I came up with 55mm (5.5cm), so given +/-1mm you're right on in your assumption! Now how does that relate to the shimmy?! I've read that the more trail the more stable a bike will be steering wise, but also less responsive. But does it also mean that there is a point in which there is too much trail for highspeed stability or would the bike just not be manuverable above a certain amount of trail and speed? Also wondering do you not see it as a problem that a bike shimmys while rideing nohanded at say 25mph (honestly wondering), I mean I don't want to seem as if I have unrealistic expectations on a bike but isn't it sort of a red flag?! I would also be more alarmed if this happened while on the bars but still 25mph isn't all that fast. I would be more understanding if it occured during 50mph no handed descents, I guess that's maybe cause I won't be doing much of those...
Thanks!

My opinion is that if it happens no hands, it's trying to shimmy with your hands on the bars, in fact it probably is, just damped enough that you don't notice the slight S-shaped track.

What kind of tires are you using and what is the frame built for?

Orin.

[CJH]

Hi
I've tried two sets of wheels first one is Open Pro's Record hubs with Veloflex Pave tires the 2nd set was Nucleon with Vittoria Open Corsa EVO CX tires. As for what the frame is built for, I'm not sure I understand your question?! Riding, raceing, paceline etc?
Thanks!

[Smiley]

We'll one thing that I try to design or convey in my fit assessment when sending a draft to Serotta is trail based on where a rider sits on the bike ( center of gravity ) . For a 58 cm frame I really like a trail of + 5.8 , people might disagree with me but not Serotta as I think thats what they shoot for on their larger frames now . Your front end will be fast and fast gets compounded when your going at high speed de-weighting the front wheel . I say find a shorter rake fork and adjust the trail to a longer figure and see if this is still a problem . What rake and brand fork do you have ? If its steel maybe a frame designer can help out . I had Dave Kirk build a custom fork for a client of mine cause we could not find a carbon fork with a 55 mm rake . Keep us abrest of the findings .

[Orin]

Hi
I've tried two sets of wheels first one is Open Pro's Record hubs with Veloflex Pave tires the 2nd set was Nucleon with Vittoria Open Corsa EVO CX tires. As for what the frame is built for, I'm not sure I understand your question?! Riding, raceing, paceline etc?
Thanks!

Size of tire mainly. It makes a difference to the trail. If the design anticipates a fatter tire, then you can design with a lot less trail - a fatter tire has a greater self-centering effect and requires less trail.

Orin.

[Kurt]

I think the few responses is because wobble is well documented via google or other bike sites. I was thinking about the notion of taking the hands off to get a vest off @ 25 – not sure I would try that trick, but I do think the frame should be like a rock at low speeds and certainly should descend well into the 40’s – I think you will be able to see pretty quick if it get out of shape or not. I had a csi that I got 5 years ago and I was so slow and fat that I never noticed anything wrong for years, but once I lost 50#’s and started racing it was apparent that the frame was flawed – amazing that both the bike shop and Serotta would sign off on a frame with a long tt and short stem, I think that combo spells trouble in a 58, but whatever – it really shows that one has to be really part and connected to the process in order to get good results. Its hard to describe but my csi never felt planted, almost light at the front end – I don’t know if it was a stiffness issue in combonation with the geo or not. Serotta could never find anything wrong with the frame, but did warranty it after 4 years, which is pretty amazing – they gave me credit for whatever I wanted so I tried out an os legend with more balanced geo and I am delighted with the result. Btw, it turns out that we use the identical size so if you don’t get resolution and want to dump that awful frame shoot me an email, heck – all you are going to do is ride around the park and do lunch @ Mercer kitchen or Balthazar, what do you need a fast bike for anyway? Was last in NY to see the Gates, what a great city.

[CJH]

Yep! That's pretty much what I ride around the park and have lunch at said places... But you must have a very quick front end in NYC, so as to be able to dodge the traffic! On a more serious note I'm trying to be cool about it since I haven't heard back from LBS or Torelli yet. We'll see what they come up with? But Smiley your sugestion that a 58 needs 5.8cm of trail is interesting, if it comes down to that I could essentially get a fork with less rake and acheive that, hmm?? The steel fork I have on there now is a brazed Mondonico ELOS fork. Maybe they can make one with the appropriate rake?! As for the tt length stem length combo that should really only be an issue when riding with hands on the bars no?! However the links presented at the start of this thread, particularly the sheldon link, seem to suggest that weight distr. has no effect on shimmy! Not what I would've thought but my experiment with sitting as far forward as well as far back on the saddle as possible with the same shimmy result, same speed etc. seems to indicate that this statement is true?! The links also go on to suggest that trail in fact have little if anything to do with it. Torsinal flex in the top tube, front end is stated as the culprit. Whatever the "truth" is it's been great getting all this valuable info, experience for my future disscusion with the LBS and Torelli. Thanks alot guys I really appreciate it!!! Oh! Naturally I'll let you all know how it plays out!

[dirtdigger88]

my 60cm has 5.9 cm of trail- no shimmy here!!!!

Jason

[Kurt]

Yep! That's pretty much what I ride around the park and have lunch at said places... But you must have a very quick front end in NYC, so as to be able to dodge the traffic! On a more serious note I'm trying to be cool about it since I haven't heard back from LBS or Torelli yet. We'll see what they come up with? But Smiley your sugestion that a 58 needs 5.8cm of trail is interesting, if it comes down to that I could essentially get a fork with less rake and acheive that, hmm?? The steel fork I have on there now is a brazed Mondonico ELOS fork. Maybe they can make one with the appropriate rake?! As for the tt length stem length combo that should really only be an issue when riding with hands on the bars no?! However the links presented at the start of this thread, particularly the sheldon link, seem to suggest that weight distr. has no effect on shimmy! Not what I would've thought but my experiment with sitting as far forward as well as far back on the saddle as possible with the same shimmy result, same speed etc. seems to indicate that this statement is true?! The links also go on to suggest that trail in fact have little if anything to do with it. Torsinal flex in the top tube, front end is stated as the culprit. Whatever the "truth" is it's been great getting all this valuable info, experience for my future disscusion with the LBS and Torelli. Thanks alot guys I really appreciate it!!! Oh! Naturally I'll let you all know how it plays out!

As for the tt length stem length combo that should really only be an issue when riding with hands on the bars no == stem might not matter, but I thought my tt was too long and really the whole thing not stiff enough, esp in the front end - nothing I can prove, just a feeling comp to my current ride, which has a trail of 5.59cm

http://www.kreuzotter.de/english/elenk.htm

[CJH]

I see what you're saying Kurt! My top tube is 57.5 on a 58 frame so on paper at least it's not overly long?! But you're right in that it might still not be stiff enough?! I just sent an email to my LBS suggesting the issue of trail be discussed with Torelli, we'll see how that goes. Maybe trying a few diff. fork rakes (less rake) would be good?! When I measure my fork it seems to have 43/44mm of rake. It is brazed stell, anyone know if it's possible to alter the rake of the blades (they are the bent kind)?
Thanks!

[marle]

I'd sell the bike..why wait for the crash?

[Kurt]

I see what you're saying Kurt! My top tube is 57.5 on a 58 frame so on paper at least it's not overly long?! But you're right in that it might still not be stiff enough?! I just sent an email to my LBS suggesting the issue of trail be discussed with Torelli, we'll see how that goes. Maybe trying a few diff. fork rakes (less rake) would be good?! When I measure my fork it seems to have 43/44mm of rake. It is brazed stell, anyone know if it's possible to alter the rake of the blades (they are the bent kind)?
Thanks!

yeah, your tt seems fine, the same as I am riding - man, it could be almost anything - this thing is under warranty right? This rests in the laps of the lbs I would think - if you ride bike A and it has an issue and bike B does not, well you get it. you should not have to play designer with forks and such, we just all want to ride right? LBS baby.

[Smiley]

I really only suggest that the trail will stabilize or slow the front end effect . Bikes with Shimmy can be altered by some very simple changes like an OS TT or a different fork , maybe different trie pressure or tire radius . Bet if you put a Reynolds fork on that sucker it all goes away . I'd then be given the choice of what rake to pick , me says 41 mm , unless Span is different . Look worst case try a different fork any different fork even a steel one .

[CJH]

To be completely fair I only noticed this yesterday and upon trying two different wheels and some weight distr. experimentation called and spoke to my LBS who asked for a list of the gear on the bike and said he was going to run it by Torelli. Thus far I've just recieved an email saying he's passed the info to Torelli who is now working on it! I then proceeded to email some thoughts and ideas from this board and some other links to be helpful or to keep them on their toes (make your pick). I feel it's a little early to conclude what needs to be done thus far. However this discussion has been very helpful in many ways. Regardless of who has to deal with the issue it never hurts to be well informed. Just to clarify it is a brand spanking new frameset so I assume it's a warranty issue or Torelli's responsibility however you choose to frazee it. Anyway thanks again you guys are GREAT!!!

[Smiley]

I bet you they won't consider it warranty . Serotta has taken back one or two frames based on shimmy , one person that comes to mind is Flydhest , who got a Legend Ti due to shimmy on his CSI , ironically he has a used CSI with NO shimmy now and his CSI shimmied without the use of an F1 fork if I recall properly . Your bike wobbles under a no hands condition which is a HIGHER standard to judge this frame by especially since its at a critical frequency or speed , Would or does this frame shimmy at say + 30 mph with no hands ? I am interested to know the outcome. By the way Fly got an over sized and I mean over sized Legend ti and F1 fork and No shimmy , now he has a CSI with stock steel fork and no shimmy . Go figure .

[Kurt]

I bet you they won't consider it warranty . Serotta has taken back one or two frames based on shimmy , one person that comes to mind is Flydhest , who got a Legend Ti due to shimmy on his CSI , ironically he has a used CSI with NO shimmy now and his CSI shimmied without the use of an F1 fork if I recall properly . Your bike wobbles under a no hands condition which is a HIGHER standard to judge this frame by especially since its at a critical frequency or speed , Would or does this frame shimmy at say + 30 mph with no hands ? I am interested to know the outcome. By the way Fly got an over sized and I mean over sized Legend ti and F1 fork and No shimmy , now he has a CSI with stock steel fork and no shimmy . Go figure .

I think it is waaay more than several frames they have taken back, add my csi to fly's and I have heard of others. I think the frame should be stable for whatever you want to do with it - I go hands off to eat, not as 25 mind you and if my bike had a shake it would be history. If serotta did not handle my exchange the way they did I would be on a moots now - they are beyond stand-up, I have decals just on my downtube, wore off - 3 sets via fedx the next day. The frames might be expensive, but the customer service is hard to beat. My bet is torelli will take care of it no problem.

[Smiley]

Kurt , your preaching to the choir , As an ex-rep for Serotta I can't tell you of the stuff they did for maintaing client relationships , but are were not talking about Serotta in this case . Thats why we want to know the outcome. I think he should get another frame .

[mdeeds71]

This thread has me thinking...I will be first to admit my skills on a road bike are lacking...But if I try to go hands off on my CDA...I have to sit upright in order to maintain a balance...When riding at 20+ mph I can go hands off but again get a wobble...not a shimmy...I beleive it is my ability and sence of balance...As for my MTB I can go hands off anytime and be balanced...

Someone please tell me that this is my ability and not my bike fit/finish...I soon will have a second Serotta Colorado II to see if it is my ability (sucks) or the bike...

[CJH]

Smiley I wish you would be the one who decided the policy in this case! I guess I'll find out shortly. Oh! A new detail to the whole shimmy rider related issue. So I had a friend of mine ride my bike as well, same thing happens at the same speed and mind you he's built quite differently from me. I'm 6ft and change 164lbs not exactly the most powerful of riders! My friend is muscular (strong) at 5.9ft and 187lbs. So assumeing that's different enough I assume it's not rider related! TO BE CONTINUED...

Thanks!

[Birddog]

Leonard Zinn used to host a segment of a bicycle testing show on OLN. On every show I saw, he would test the bike by riding with no hands looking for shimmy. He remarked that on the size frame he rode (usually the biggest the co could get him) it was fairly common. He never really expounded about it, but I got the idea that he felt a bike was better if it didn't shimmy, although he wasn't too shook up about it if it did. He just sort of accepted it as "par for the course".

Birddog

[shaq-d]

since u have a steel fork, it's also possible the fork is bent, in which case they can align the fork very easily.

sd

[vandeda]

You know ... I've forgotten the stuff I've read about shimmy. But I have a question. I noticed that sometimes my Centurion, when heavily weighted out back, so the front end is light, will shimmy a little bit around 25 mph, but then die down again at lower or higher speeds during no hand riding. The fact that it was right around 25 mph, but not below or above that speed made me think I was seeing some natural frequency between the wheels and frame occuring.

This was much like in my '00 Miata, the natural frequency of the wheel/tires would excite the frame of the Miata around 55-60 mph and cause the chassis to shimmy. Known "problem" for 2nd generation Miata's because the natural frequency of the Miata's chassis was just right to be excited by the natural frequency of the wheels/tires. Unless the tires were perfectly balanced (and your standard tire balancer usually was insufficient to do that job either), the frame would shimmy at these speeds. So above or below the 55-60 range, smooth riding, but in that range you could have a vibrating chair. Hmmm ... much like my Centurion, or so it seems.

So my curiousity is ... what happens at 30 mph CJH? Or 35 mph? Hmmmm .... but do we really want to try this? What if the shimmy is worse, the results could be .... bad, and I would never want to see you get hurt for such a silly test. Just something that came to mind based on my past observations ...

NOTE!!!: One difference, holding the steering wheel tighter, looser, or taking my hands off in the Miata made no difference ;)
Dan

[CJH]

Hi!
So now I feel kinda' silly!!! However I won't eat it all myself... Anyway so after much deliberation back and forth reg. this shimmy issue btw. me, LBS, Torelli and supposedly Mr. Mondonico and an assurance from my LBS that this will be resolved even if takes a new frame to do so! Which in my mind shows great comitment! Credit to them. However when I picked up my frame at the LBS when I originally bought it I had them install a threaded headset that I supplied, a beautiful NOS 1996 Record headset by the way. I then proceeded to build up the bike and all was well until I came across this shimmy issue.

Waiting for the LBS to contact me with our next step in this saga I was fiddling with my bike and noticed that when I tightened down the headset locknut useing only one wrench the 2nd nut did not turn as well, which is usually the case if the washer is not "keyed". Hmmm! I then realized it could only mean that there was no contact between the two! Steerer too LONG! However somehow I was able to "adjust" the headset enough that I couldn't feel any play in the setup! Anyway long story short I cut the steerer 2mm tightened everything down, no play, smooth etc and went for a ride. The gods must have been smiling cause there was no more SHIMMY! Not at 25mph or 30mph or 35mph no-handed. It's steady as if it were on tracks... So as you can imagine I feel a bit silly for not haveing checked this. Actually I did check and adjust the headset and there was no play in the headset that I could detect! Obviously there was something a miss though.

Funny thing though, while doing some research on the issue two seperate articles on shimmy one by Jobst Brandt and one by Tom Kellog clearly state that shimmy has nothing to do with headset adjustment! Oh well! It dosen't matter much I'm just happy I came across the solution! Thanks again all who where so helpful and supportive in this issue and hope the solution wasn't too much of a dissapointment! ;)

[Kurt]

Hi!
So now I feel kinda' silly!!! However I won't eat it all myself... Anyway so after much deliberation back and forth reg. this shimmy issue btw. me, LBS, Torelli and supposedly Mr. Mondonico and an assurance from my LBS that this will be resolved even if takes a new frame to do so! Which in my mind shows great comitment! Credit to them. However when I picked up my frame at the LBS when I originally bought it I had them install a threaded headset that I supplied, a beautiful NOS 1996 Record headset by the way. I then proceeded to build up the bike and all was well until I came across this shimmy issue.

Waiting for the LBS to contact me with our next step in this saga I was fiddling with my bike and noticed that when I tightened down the headset locknut useing only one wrench the 2nd nut did not turn as well, which is usually the case if the washer is not "keyed". Hmmm! I then realized it could only mean that there was no contact between the two! Steerer too LONG! However somehow I was able to "adjust" the headset enough that I couldn't feel any play in the setup! Anyway long story short I cut the steerer 2mm tightened everything down, no play, smooth etc and went for a ride. The gods must have been smiling cause there was no more SHIMMY! Not at 25mph or 30mph or 35mph no-handed. It's steady as if it were on tracks... So as you can imagine I feel a bit silly for not haveing checked this. Actually I did check and adjust the headset and there was no play in the headset that I could detect! Obviously there was something a miss though.

Funny thing though, while doing some research on the issue two seperate articles on shimmy one by Jobst Brandt and one by Tom Kellog clearly state that shimmy has nothing to do with headset adjustment! Oh well! It dosen't matter much I'm just happy I came across the solution! Thanks again all who where so helpful and supportive in this issue and hope the solution wasn't too much of a dissapointment! ;)

glad you got it taken care of, just in time for the weekend :D remember, thats my size when you get tired of it.