NuVinci cargo bike revisited

Last month I wrote an article describing various internal hub transmissions as alternatives to the derailleur-gear system found on most bikes in the U.S. I was especially intrigued by the updated NuVinci hub, which uses a clever mechanism consisting of rotating balls in a fluid bath. A friend directed me to this blog post, which (along with the comments that followed) only increased my interest in the possibilities of a Nuvinci-based cargo bike.

A few days ago, I received the October 2010 issue of A to B magazine.  If you aren’t familiar with that publication, it is a British magazine that reviews various bikes, often with a heavy emphasis on folding and electric models.  I’ve learned a lot from reading it, and I love the attention and detail they put into testing and describing each bike.  However, because it is so focused on Britain and Europe, I often have to translate into my American experience almost as if it were written in a foreign language.

Raleigh 360

In any case, the latest issue includes a review of the Raleigh 360 electric bike.  Although it isn’t a cargo bike, my interest was piqued because it uses a crank-mounted motor (and integrated battery) driving a NuVinci 360 hub.  That sounded like a really interesting combination to me.

The review does a good job of describing the technical details of the hub and how it works.  Their critique of its performance was mostly positive, and I would highly recommend reading it if you are considering the NuVinci hub (I believe an electronic copy of the magazine can be purchased for a few dollars; a year subscription costs 11 pounds).  But there were also a few caveats that gave me something to think about when considering the hills I must contend with:

We mentioned above that the shift quality gets heavier as pedal pressure increases.  Add the stonking torque of an electric motor and the shift more or less seizes up.  There are two ways round this: you can either relax your effort, which frees the shifter but rather negates the advantage of using CVT [continuously variable transmission], or you can twist the shifter with a gentle steady pressure.  This allows the NuVinci to change gear at its own pace – you soon get to grips with the technique.  The high top gear results in a time of 31 minutes on our ten-mile commuter ride, at an average of 18.9mph (yes, we know it’s not exactly ten miles).  This is rarified territory for an electric bike, and the Cytronex is the only legal bike that outpaces it. Compared to similar crank drives, this bike is broadly one to six minutes faster over this sort of range, which doesn’t sound much, but it’s noticeably quicker.  That’s not to say it’s more efficient though.  The Raleigh 360’s high top gear, and gloopy happenings in the hub, result in power consumption of 14Wh/mile, which is unusually high for a normally efficient bike like this. If you like to commute in fast, furious style, power consumption might not be your top priority, but a clear picture is beginning to emerge: the NuVinci is smooth, fast and tolerably efficient on the flat, but a real pudding on hills.

There is a lot more detail in the 5-page article than I have included here.  I’ve begun to see that there are two sides to the NuVinci story, and your local geography might be the determining factor whether it’s good technology for you.