Wednesday, 3 August 2011

Bad Vibrations

Shimano Alfine Hub
Riding my Rivendell last weekend, I was going downhill when I became aware of a strong vibration in my hands from the handlebars. At first I thought I was imagining it: This felt like "shimmy" and I know this bike does not have shimmy; this has never happened before. Was the headset loose? At the bottom of the hill I stopped to check, but everything seemed fine. Then I noticed that my lights were on. I must have forgotten to turn them off from the previous night. And then it hit me: Could this be the dreaded high-speed dynamo hub vibration? Jan Heine mentioned it in a recent Bicycle Quarterly article, and Somervillain reported it after building up his latest bike. In both cases, Shimano hubs were involved. The hub on my bike is a Shimano Alfine.

I turned off the light and began to cycle again, picking up speed. No more vibrations. Turned the light back on and picked up speed once more. Again the handlebars began to vibrate. Yikes. The only way I can explain not having noticed this earlier, is that I must have never gone this fast with the lights on before - which makes sense, because I normally only turn them on when it's dark and I cycle slower  in the dark. This time I accidentally left them on in the daytime, and when I first noticed the vibration I was going about 25mph. But once I began to pay closer attention, I could feel it starting at 17mph or so.

Schmidt SON Dynamo Hub
The following day I rode the same route on the Randonneur and intentionally turned the lights on. This bicycle is equipped with a Schmidt SON Delux hub. I did not feel handlebar vibration at high speeds. Reading up on this issue some more, the vibration effect has been reported for many different hubs, including Schmidt - though not the SON Delux model specifically, as far as I can see. Is the SON Delux immune to this?

I am frustrated to experience the vibration on my own bike with the Shimano Alfine. At the time I was choosing a dynamo hub for this bicycle, the considerably more expensive Schmidt seemed frivolous, and everyone assured me that in practical use (as opposed to efficiency tests) the new Shimano models worked just as well. However, my recent experience appears to contradict this. It is disappointing to learn that I am limited to cycling at speeds below 17mph if I want to have the lights on without my handlebars vibrating.

Some have suggested that it is not the dynamo hub itself that's responsible for the vibration effect, but that it is a complex interaction between the hub, wheel size, and frame. That could very well be, and if so it will take forever to uncover the pattern of causality. What have been your experiences with dynamo hubs and vibration at high speeds?

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