Shimmy is typically very speed dependent. When ride-buddy JimG was diagnosing his issue on a non-RBW bike, it shimmied in a very predictable pattern when using a front bag, rear load and unloaded. ). They were not equivalent speeds - 15, 18 and 21 mph IIRC.
It's also extremely center of gravity dependent. I've seen it more with lighter, taller riders, and by sitting back and up, you are taking what little mass you have up off the pedals and pitching it back and behind. You might experiment slightly with the angle of your hips when you go no handed. The reason I mention this is that I've found minor differences in how I sit makes a great deal of difference in where the COG is located. It's not important on my RBW bicycles, but I have an older fixed-gear bike where weight distribution is a lot more critical. My suggestion for removing the saddlebag was really one of identifying variables. As far as differing speeds on differing hills: I'd go back to COG. The steeper hill does effectively move it forward. On the Jack Browns, after I got my first pair, I had to really force myself to go back and use up the old Paselas... - Jim On Tuesday, April 23, 2013 11:02:51 AM UTC-7, john wrote: > > Well, after removing the tire from the new wheel, remounting the tire to > ensure a perfect seal, and matching up the valve to the label for future > testing, and ensuring that the wheel was perfectly centered in the fork, I > got out for some more testing. > > One thing that has changed since my initial tests: I no longer provoke > shimmy at a slow speed, only a decent clip. However, when descending a hill > at moderate speed or fast speed, if I'm sitting upright with hands off the > bars, my Sam Hillborne will dance. Frustrating. > > Of course, Charlie is right: I could just right with my hands on the bars. > But for me, riding no-handed down hills not only is relaxing, but a great > joy. So at least for me, it's not an option. Or at least not one I'm > willing to consider at this time. > > And as others have suggested, i could ride without a saddlebag. But after > using saddlebags for 20 years, I wouldn't even know how to ride without my > beloved saddlebag. (And furthermore, although I'm sure a weighted saddlebag > is a factor, I have not had any significant weight in my saddlebag > throughout this discovery process. Not to mention when I ride the old wheel > with the same saddlebag, I experience no shimmy.) > > How to explain the initial shimmy at slow speeds and now only at higher > speeds on a steeper hill? Perhaps the tire is seated better than initially. > Perhaps the rubber of the tire has expanded over the course of a day. Who > knows? > > I guess the worst case scenario is I go back to my old wheel with > fantastic new Jack Brown Greens. Wow, I love those tires! I was > anticipating a let down, going from 35c Panaracer Pasellas to a "skinny" JB > 33.3c. To the contrary, I'm really loving the tires and don't notice the > width as being a factor. Time will tell about puncture resistance. But as > far as ride quality, much improved on the JBs. > > Thanks for everyone for sharing his opinions and anecdotes. Much, much > appreciated. I will update this thread if and when I am able to solve the > riddle. But I suspect I will just swap back to my old wheel for the time > being and quit worrying about it. > > If any of you out there is interested in a new Shimano Alfine generator > hub on a new Syngery Velocity 32 spoke wheel, I may just be willing to part > with it. > > thanks again for sharing. > John > > > On Tuesday, April 23, 2013 7:12:08 AM UTC-7, Tim McNamara wrote: >> >> Wheel balance on bikes is a red herring. The mass differences are too >> small and the RPMs of a bike wheel are too slow. >> >> I have another anecdote that I don't have time to write at this time (at >> work, should be working...) which should help demonstrate this. >> >> On Apr 23, 2013, at 8:35 AM, Will <[email protected]> wrote: >> >> > I've always felt that shimmy was related to an unbalanced wheel. We >> routinely balance our automobile wheels, why would a bike be different? >> > >> > I think as we move to fatter tires (more mass) we will need to address >> the balance issue. I think the frame discussion is irrelevant. >> > -- 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en-US. For more options, visit https://groups.google.com/groups/opt_out.
