Unfortunately, nobody knows what causes shimmy. What I mean by that, is that there is not a human being on earth that look at your bike and say "your bike shimmies and here's why". If we took 9 bikes that don't shimmy and 1 that does and put them in a lineup, there is no human that can look them over and pick out the shimmying bike. If we took a non-shimmying bike to the workshop there is no mechanic that can do work on it to cause it to shimmy.
What we do know is that shimmy is a resonant oscillation, and everybody who knows anything about resonsance knows that if it is resonating, then everything that is important is just right in that oscillating mechanical system. To stop it, you change something that is important. How do you know what's important? Take a guess and start changing things. If it helped, it was important. If it doesn't, either it wasn't important or you didn't change it enough. A needlebearing headset has proven to be effective because it adds damping to the oscillating mechanical system. It's still resonating, but the amplitude gets scrubbed off and the self-amplifying part of the resonance fades away. (for electronics geeks, damping reduces the Q of the system). The damping from a needlebearing headset is from friction. A needlebearing headset does not turn as freely. Weight distribution on the bike can be quite important, and is the only thing you can easily make major changes to. Some people guess that tire width and tire pressure can effect shimmy. Some speculate that frame stiffness and steering geometry influence whether or not a bike will shimmy, but you are stuck with those things. Bill Lindsay El Cerrito, CA On Tuesday, August 23, 2016 at 9:02:58 AM UTC-7, Tony McG wrote: > > From the beginning: The original owner purchased it as a frameset in '99 > because at the time, the future of the Atlantis was questionable. He built > the bike and never rode it because he found a Waterford that he liked > better. I bought it barely used a few years ago and have put a few thousand > miles (mostly gravel) on it. The headset would never stay tight no matter > how hard I dared wrench on the locknut. I took it to a LBS and they removed > the headset and machined the frame so that the headset would fit better. I > rode it for a year, and I still had problems with it loosening. I then took > it to another LBS and they installed a spacer (seems like the headset might > have bottomed out on the threads???). I now have a tight headset, but > I also have a shimmy when I let go of the handlebars. I used to be able > to ride this bike without hands at any speed, but now it wobbles, even at > 10 mph. I don't have any load on the bike except a small seatbag for > tubes/tools, and the tires are the same Soma Cazadero from last year. > > Any suggestions on what might be causing the shimmy or how to fix it? > Shall I replace it with a NeedleBlasteur from the Riv site and see what > happens? > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at https://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
