The thread on shimmy has been enlightening. When I worked in bike shops, there were several times that people came back with this complaint. It was almost always on reacing geometry frames, and in taller sizes. We had the largest number of complaints on the early '80s Treks, so I think geometry has a lot to do with the issue. I also thought the Trek frames were pretty flexy, and that may have played a part as well. I wish I had known about the tricks of rising off the saddle and putting a leg against the TT to dampen the harmonic.
The most disconcerting experience I had was with a customer who came back with a Marinoni that I had sold him. He was convinced that the shimmy he had experienced on a descent on one of his first rides was due to frame misalignment. He had taken the bike to a local "framebuilder," a guy who had built only a half-dozen frames, but who had one of those portable alignment jigs that was popular among hobby builders at the time--it attached to the BB and then had a moveable arm that could be used to measure from to establish alignment. Anyone remember those? Anyway, this guy had torches, this jig, a beard, granny glasses and an ego, so that made him a guru.
So, what did I know? Maybe these frames that I was so hot about were not all that good after all. Who was I to argue with a guru? So, I stripped the bike and took the frameset back up to Marinoni's shop in Montreal.
I explained the alignment issue to them and was shocked when they just laughed. Guiesseppe Marinoni brought me to his alignment table and carefully measured out the frame, demonstrating to me that the alignment of the frame and fork were perfect. Before you say "maybe his alignment table was off," I have to note that he mounted the frame to the table from both sides and checked in enough different ways that I could see that simple geometric principles showed that the table and frame were both in perfect alignment.
What really surprised me was their attitude. They were not at all consescending, but there was no doubt in their minds that their all their frames were straight. I imagine you experienced framebuilders know what I mean. As a person who had stromg doubts about the product when I went in, I was impressed by their faith in their workmanship.
Steve Barner, Bolton, Vermont, where it is way too nice to be sitting here writng email.
If someone doesn't clue them in that all bikes will shimmy if their natural vibrating frequency is initiated by a shiver, being too tense hitting a small rock in the road etc. their opinion is that they have a "killer" bike. Then they start looking at the headset, wheel construction, etc.; all the wrong things. They even sell the bike and bad mouth the builder!