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  1. #1
    Armageddon wasted.
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    Front end shimmy wobble?

    I just finished a SF-LA tour, during which I felt a constant (and rather infuriating) front end wobble, or shimmy, even at relatively low speeds. I've toured plenty before on my 80s Schwinn World Tour, without this problem, but this was the first I'd tried it with a front rack & panniers. My rack is an old Blackburn Mtn. rack, which is NOT a lowrider. Would a lowrider-type rack help (lower center of gravity)? Less weight on the front? More weight on the front? Any suggestions would be helpful.

    (I searched "shimmy" and "wobble" on both Google and Bikeforums, and came up with few answers, so hopefully this one'll help future searchers!)

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    I'm guessing a low rider would have made the difference but your experimenting is the best answer.

  3. #3
    BE the Ferrari. supersport's Avatar
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    Experiment with the weight on the front, would be one way to find out.

    If you figure it out, I'd be interested in hearing.

  4. #4
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    I have experienced some handlebar shimmy, and traced the cause to two different things. The first was unbalanced load in the front panniers, and the other (more important) was a handlebar bag with some freedom to swing beneath the bars. Make sure that your load is balanced and if you use a handlebar bag, try securing it well and not putting too much weight in it.

  5. #5
    Senior Member rumrunn6's Avatar
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    interesting hat it occurred AFTER adding weight on he front. but gorshkov's advice makes sense based on what I've read about it.

    I've been following front wobble/shimmy for some time and there is a lot of information about it out there. keep looking. you might also enjoy researching the dreaded "death wobble"
    cycling is like baseball ~ it doesn't take much to make it interesting

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    I will be interested to read the replies to this. I have only done one short tour and almost turned back after a couple of hundred metres because the low speed wobble was so bad. My bike is a 26" tourer with 631 tubing and has a good reputation. I had light front panniers on low riders and a light handlebar bag that is very solid. The wobble was very bad at slow speeds and reduced as speed increased. When freewheeling downhill it felt rock steady.

    For various reasons I am thinking of trying a high front rack rather than low riders so whether that will make it worse or better?

  7. #7
    friction baby, friction D.B. Cooper's Avatar
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    I had the same problem with my girlfriend's Trek 720 on a cross country tour. The problem started from day 1. She had trained on the bike, but never fully loaded. We took it to a bike shop in Port Angeles, Wa. where they took apart the headset thinking that was the problem. The cups and bearings were fine. We chaulked it up to being an old bike that developed a lot of flex from use. The guy that I bought it from had toured Europe on it . We nicknamed it 'The Noodle' and persevered. The Noodle got her home, 5,164 miles later. BTW, she had lowrider racks on the front.
    1984 trek720
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  8. #8
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    Loose hub cones?
    "I've wanted you to succeed, but watching you find excuse after excuse after excuse and then laugh it off as the loveable, quirky, chubby guy is getting old."--Ill.Clyde

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    1.) headset adjustment- it might be a *smidge* too tight.
    2.) getting the load in line with steering axis. (center the weight in front of/behind the line between center steertube and axle)
    3.) lowriders

  10. #10
    Crazyguyonabike
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    I have had shimmy problems with most of my touring bikes - a British Raleigh Randonneur (circa 1998), a Bruce Gordon Rock 'n' Road from 2003, a Novara Safari from 2008, and a Salsa Fargo from last year. In all cases except for the Bruce Gordon, it seemed to me that the frame flexed excessively when I had a full touring load.

    Shimmy has many different possible causes, including weight distribution, frame geometry, worn components (e.g. headset bearings) and even unevenly mounted or damaged tires. My personal theory was that my shimmy problems were caused by the frame being too flexible, since it always seemed to me that I could feel and see the frame flexing with a full load, and this flex is what set up eventually as the harmonic wobble, or shimmy. For this reason, I decided to try to find a bike that was as strong as possible. The Co-Motion Americano caught my eye, because it was built with tandem specs - big tubing, monster chainstays, 145mm rear hub etc. So I eventually went and did a test ride with a full load, and that bike did not shimmy at all. I don't know if it was due to the stronger frame, or maybe some other factors as well related to geometry, but all I do know is that I finally found the bike that doesn't seem to want to wobble all over the place when I put a load on it. (Full disclosure - I got a pro-deal from Co-Motion for a discount on the bike in return for an ad on my site, but the deal did not include me promoting their bikes in any way, and I never "shill" for companies - these are just my honest opinions).

    So, my opinion is that sometimes a bike just shimmies, and sometimes you can do something about it, sometimes not. With my previous bikes I tried everything - moving weight around etc, but nothing seemed to affect it. Remember that the biggest weight on the bike is you, the rider, so if the harmonic wobble is being caused by your position on the bike, then it's really just a matter of finding a bike that doesn't do that.

    In my opinion, you should always test ride a prospective touring bike with racks and fully loaded panniers before laying down the cash. Many people don't seem to realize that a bike handles very differently under load.

    Neil

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    I don't think tubing flex is the main cause, there are lots of people who don't get shimmy and have relatively light bikes. There are also folks who build expedition weight frames like Sakkit and there have been the unhappy few who got bad shimmy from them. We are talking integrated racks and panniers. I think there is a thread here from years back.

    As far as I know the Co-Motion frames are not built any particularly stout unless you believe front end shimmy is caused by the thickness of the chainstays or the spread of the real axle - the front end tubing or forks are nothing special to write home about in a Co-Motion. The really anoying shimmy I have had was in the front fork region and around the headset. A side to side wobble around the head tube. How is that coming from the rear end, in most/any cases? Generally it was easily solved with repacking the front end, but obviously that hasn't worked for others. Complex issue.

    The worst day I ever had was when I packed the front end after careful weighing, and had exactly equal weight on both sides. As soon as I got stuff packed out of balance shimmy went away. High speed shimmy that occurs in unloaded bikes can be quelled by how you hold the bars, interesting to contemplate.

    I don't believe how high the panniers are is important. Some of the best racks out there are high. I built an integrated porter rack for touring, and the weight could be very high on it. No problems.

    One thing I do believe is that placing weight to the rear of the front wheel axle, relatively, can be helpful. This is one thing that a high rack tends to aggravate. I have a low rider where the bags ride well aft of the front axles and it sorta tillers the front end, very helpful, and also relatively rare. To see whether this helped one could locate some weight well back in the fender area of the wheel. Or in the rear pockets of some front panniers. A chunk of steel etc... When I built my first rack with this feature I didn't know what to think, but it worked. It is a lot like trail, or delta in wings.

    Look at the front edge of the front rack frames on these low riders, "The custom front rack" :

    http://www.sandsmachine.com/a_arv_r1.htm

    They are located at the axle. That is not the normal low rider position, but it works really well.

    Same result, to some extent, could be achieved by putting heavy stuff, cans of tuna or fuel, at the rear edge of the front panniers. Problem with that is that in trying to get as much weight forward as possible, I already have all my heavy stuff in the front end , which makes it hard to get a significant density redistribution to the rear, in my case anyway. So I appreciate the rack I have.
    Last edited by NoReg; 03-09-10 at 05:09 PM.

  12. #12
    Crazyguyonabike
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    Quote Originally Posted by Peterpan1 View Post
    I don't think tubing flex is the main cause, there are lots of people who don't get shimmy and have relatively light bikes. There are also folks who build expedition weight frames like Sakkit and there have been the unhappy few who got bad shimmy from them.
    Shimmy is caused by hitting a harmonic frequency - that's the end result, but there are many different ways to set that up. If the bike flexes, then that flex can set up as the shimmy if you hit the right harmonic. I guess for many people, their height, bodyweight, riding position etc mean that they happen to not hit that frequency within the range of speeds that they normally ride at. Perhaps I am just a little unlucky in that for frames my size, and with my height and weight etc, I am more likely to hit that frequency.

    Most framebuilders will tell you that they cannot guarantee that a bike will not shimmy - any bike, loaded or unloaded, could shimmy at some particular speed or other set of circumstances (taking your hands off the handlebar, or one hand, etc) - but it's almost impossible to predict in advance. Shimmy can have many different causes, but the end result is that the entire system hits that harmonic. Frame flex by itself doesn't guarantee shimmy; but it may contribute to a tendency for shimmy for certain people. At least, that was my intuition, and it seems to have been borne out by my tryout with the Americano.

    As far as I know the Co-Motion frames are not built any particularly stout
    What are you basing this on? As far as I understand from my talks with Dwan Shepard, and my visit to Co-Motion's factory, those bikes are definitely built stronger than usual. For example, they use large diameter tandem grade tubing throughout, and I think those big chainstays do contribute to less frame flex. No, I can't give you numbers to "prove" this, but that is just my impression gained from many conversations, and actually seeing the bikes being built. And, again, having ridden a few different loaded touring bikes, I can detect a definite difference in the lack of flex on that Americano, and a corresponding lack of shimmy. Anecdotal perhaps, but I had a hunch and I think it turned out to be correct.

    I think that the stiffer frame might help to prevent shimmy by damping down the oscillation that would otherwise build up in a more flexy frame.

    A side to side wobble around the head tube. How is that coming from the rear end, in most/any cases?
    I thought it was generally accepted that shimmy can happen because of weight being too far back behind the rear hub, causing a "tail wagging the dog" effect. So, longer chainstays are useful on a touring bike, because they mean you probably won't have to move the rear panniers too far back in order to avoid heel strike.

    The worst day I ever had was when I packed the front end after careful weighing, and had exactly equal weight on both sides. As soon as I got stuff packed out of balance shimmy went away. High speed shimmy that occurs in unloaded bikes can be quelled by how you hold the bars, interesting to contemplate.
    The shimmy I had on my Novara Safari seemed to get worse when I put any weight on the top of the front rack (it was an Old Man Mountain Cold Springs). I had a little cooler bag on top, for food and drinks. When it was loaded up, there was a definite funky feeling in the way the bike handled. I think for some bikes, it probably helps to keep the front weight as low as possible. How it all interacts depends on more factors than I can juggle in my head - fork rake and trail, to name but two.

    After my trip in 1998, where I could not determine the cause of the shimmy I was experiencing, someone suggested that maybe it was damaged sidewalls in my tires. Apparently this can be unnoticable to the eye, but still can cause that effect. It was certainly something I don't think anybody thought to check - they had looked at everything else, including frame alignment, wheel trueness, and brinelling in the headset bearings.

    Neil
    Last edited by NeilGunton; 03-09-10 at 06:03 PM.

  13. #13
    Cycle Year Round CB HI's Avatar
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    I have even had shimmy caused by crosswinds going over an aerobar on an unloaded road bike.

    Often your reaction to adjust for the initial bike motion can enhance the shimmy. Try holding your handlebar very lightly once the shimmy starts and see if it goes away (do not keep fighting the bike).

  14. #14
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    I think people need to be clear what phenomenon they are actually talking about. My problem was very wobbly steering at slow speeds that reduced as speed increased and wasn't noticeable at all at high speed. When I hear people refer to shimmy I usually think of the resonant vibration problem that neil I think is describing that starts at high speed. They must be caused by very different factors.

  15. #15
    Senior Member jjciiijs's Avatar
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    The one thing I did not see mentioned was the road. I have had bike react differently to roads. Shapes, surface, degee (hill), speed. A bike may be fine for everything and then one day shimmy becasue of many things. SO - ride it the smst you can before you buy. Otherwise, check everything. adjust everything and don't forget to think about speed. You may have to ride at under 22 mph and never go over or somthing like that for your particular bike.
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  16. #16
    rhm
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    My Trek 720 has sometimes had a tendency to shimmy. I've had this bike since 1983 and have had at least five different wheel sets &c on it over the years, at least three different stems, and so on. While I agree with freebooter that we need to be clear about what phenomenon we're talking about, that's easier said than done. For a while on my bike the shimmy went away when I replaced all the rear spokes; I hadn't tensioned the wheel quite right, and the wheel was flexing more than it should. Another time there was a shimmy that went away when I put on a longer stem and moved the seat forward a bit.

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    Quote Originally Posted by freebooter View Post
    I think people need to be clear what phenomenon they are actually talking about. My problem was very wobbly steering at slow speeds that reduced as speed increased and wasn't noticeable at all at high speed...
    headset.

  18. #18
    sniffin' glue zoltani's Avatar
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    So what exactly needs to be done to the headset if this problem occurs? Just loosen it a bit?
    Do you have some kind of tutorial?

    I've looked at the park tools site and headset installation and adjustment seem complicated...
    Those who are easily shocked should be shocked more often.

  19. #19
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    well, if its slightly too tight, it will cause low speed wheel flop- i.e. diving into turns, and a tendency to swoop side-side when riding slowly in a straight line...

    on a threaded headset, there are two components (on the top-side/to adjust), a threaded bearings cup (closest to the top of the headtube), followed by a washer or two and a threaded top-nut.

    You need to loosen both slightly, then hand tighten the bearing race/cup until barely tight- even bordering on loose. Then, by tightening the threaded top nut, you will lock the bearing cup in place. when you tighten the top nut, it slightly tightens the whole system- the result is that if the cup is tight to begin with, the top nut will tighten the system too much and cause it to bind. This can sometimes be remedied by loosening the bottom nut (with a headset spanner) into the top nut above.

    Incidentally, because you need to hold the bottom bearing cup while tightening the top nut, you really need two headset spanners to do this adjustment *properly*. That said, you can adjust the headset with just one, if you are careful not to let the bearing race turn during the final tightening.

    I would try this first, because the symptoms you describe have appeared on a few of my bikes when the headset was too tight... disappeared when I adjusted.

    and on a second note, one bike i had was so bad with the original shimano 600 headset that i replaced the headset with a stronglight a9 with needle bearings, and voila! the problem was fixed... too bad those are no longer made

    hope this helps

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