Sunday, February 3, 2008

Continuously Varying Single-Speed

Our flatmate is away, and I've had the luxury of littering the carport with bicycle components. Yesterday I dragged out my brother-in-law's old bike1 from under the house and fitted in the NuVinci hub I ordered in October2. I haven't had time to install the gear controller, so it functions as a single speed with a knob on the back to change the ratio whenever you care enough to hop off and do so. It seems that without the controller installed the adjustment screw slowly turns while you ride and the going gets harder, hence the 'Continuously Varying' label.

In order to fit the hub I had to respace the frame to 135mm from 126. This turned out to be really easy -- so easy that my first effort was too strong and I had to adjust it back some. The spectre of getting this part wrong has held me back from getting started when I only had a short period to work in, so I was particularly pleased with myself when I had done it. I tried to use the string method Sheldon Brown describes for checking that the two sides are adjusted evenly, but found it hard to know if I was taking square measurements. I guess it gave me peace of mind that everything was near enough.

The hub went in easy enough, although the drive side nut is quite unusual. There is a disk mounted on the outside3, then inside that is the nut which you would expect to see. Unfortunately the nut is a 21mm fitting, so I didn't have a proper spanner and had to use my adjustable. I'll have to buy a tool, as I don't want to carry the heavy wrench around in case the wheel needs to be adjusted.

Needless to say I'll let you know when I've had a chance to wire in the controller and give the hub a proper try.

[Update - After riding this setup to work today, I can report that the self-adjustment mostly happens when you apply a lot of torque. That makes sense, I guess. Unfortunately it means that just when I'm working hard to top a rise the gearing gets even harder on me! Hopefully I can fit the controller on Wednesday, which is Waitangi Day.]

  1. This bike was probably last ridden in 1991! Heather remembers trying to use it as a fallback in 1996 and finding it unrideable. The rear wheel was dead (but I didn't need that) and the brake pads are as worn as they must have been 16 years ago, but other than the abundant superficial rust it is quite rideable. And people throw their old bikes out...
  2. I received the hub in November, had it built into a wheel just before Christmas, but wasn't able to collect it in time to do anything further during the break. I've been itching for a chance to play with it.
  3. It keeps the ratio adjustment knob from coming too far out, and the controller latches to it.

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