Jan I'm extremely flattered at your almost instant reply. I don't know if that means you regularly read the list or if somebody you know does. I admire your work deeply and endorse your publication enthusiastically. Every copy of BQ I've seen has had something astonishing for me. This issue was no different. I am pleased to be a subscriber.
Regarding shimmy, it's possible that my expectations were unrealistic. I thought I'd learn some conclusive, empirically testable conclusions, and I didn't get that. That being the state of things, I'm motivated now to experiment myself. I'm certain that you encourage that, and your article actually has helped urge me to do that which I think is a positive outcome. The things that 100% can agree upon is that shimmy is an oscillation. For that reason, it is easy to assume that there should be a spring +mass+damper model that can be used to understand the system. Whatever that system is, we can also agree, I think, that there exists some excitation force is acting on that system and making it oscillate. The missing piece in the few articles I've read prior to yours is a failure to establish and define what any of these things even are. What is the spring? You argue that it is the flexing torsion of the frame, but then concede that both the stiff frames you hate nor the flexy frames you love both don't shimmy. You imply that tire flex has something to do with the system, but it's not clear to me whether you think it's part of the spring, the mass, the damper, the exitation force, a combination, or all four. What is the mass? Some suggest that it is only the steering parts, others state it is everything including rider and the rear part of the bike. What's the damper? You argue that it's the stuff that hinders rotation: headset plus riders hands, and indirectly the riders leg squeezing the top tube. J. Brandt says tire tread is also a significant damper. Regarding the excitation force, there is no consensus of what it is or where it comes from. Sheldon(RIP) said it came from the back end of the bike, J. Brandt says it comes from the spinning wheel and sometimes from the natural frequency of human shivering. You, I think, allow it to be anything, since it is the amplifying or attenuating property of the system that is important, hence the artificial whacking the top tube to get it going. If there isn't even consensus on what the system is, then there is no hope to formally construct a comprehensive understanding of that system. It very well may be that shimmy is just a property of a bike+rider system that is the unknown functional combination of numerous unmeasurable variables. If that's the real answer, then maybe you're recommendation is the only one that works: If your bike shimmies, change something If it got better, be happy or change the same thing even more If it got worse, change the same thing in the other direction If it stayed the same, change something else Again, my opinions about whether or not your article not meets my expectations does not reflect on the quality of your contributions to the cycling world. I hoped that your article starts a dialogue that gets the topic driven to a more satisfying scientific understanding. It all strikes me as voodoo right now. With all due respect, this needle bearing headset thing, especially, strikes me as voodoo. Bill On Dec 10, 10:29 am, Jan Heine <hein...@earthlink.net> wrote: > William, > > I am sorry you are disappointed with our article on shimmy. We tried > to offer summary of the factors that appear to cause or exacerbate > shimmy. After all, we know that some bikes rarely shimmy (heavy tubes, > long trail, no load, skinny tires). It appears that shimmy is a multi- > faceted problem with more than one cause and more than one solution. > To provide a complete picture, we presented other opinions on the > issue, which may help you in your own research... I find it > fascinating what people thought about these things 50 or 70 years ago. > > Most of all, we felt the need to publish this article, because we very > much like bikes with optimized handling, wide supple tires, relatively > flexible tubing, etc. The one downside of these bikes is a greater > tendency to display shimmy. Of course, your Sam Hillborne shows that > even bikes that are very different also can display persistent shimmy. > And none of our favorite bikes shimmies a lot, so low trail, front > loads, wide supple tires and relatively flexible tubing don't > automatically result in a bike that shimmies. I am beginning to > believe that all bikes have a tendency to shimmy, and depending on a > number of factors, the oscillations either are dampened or self- > reinforce. > > For your bike, if you don't already have a needle-bearing headset, I'd > give it a try. That is the only thing we have found to work > consistently in "curing" shimmy or at least reducing it so that it > appears only rarely. You may also try to switch to narrow, stiff > tires, but there are downsides to that. If you are carrying a load on > your bike, you could try using a backpack (with its own downsides). > It's hard to change the tubing or geometry of your bike... > > I don't know what you expected in the article, but I would like to > remind you that we offer a money-back guarantee for the unused portion > of your subscription. And if your experiments yield something > conclusive, please let us know. We'd love to publish your experiences > as an additional piece to the puzzle. > > Jan Heine > Editor > Bicycle Quarterlyhttp://www.bikequarterly.com > > Follow our blog athttp://janheine.wordpress.com/ -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bu...@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
