Shimano Gear Hub Input Ratio Recommendations
- Per a phone conversation today with Shimano technical support the
following information was received.
Shimano recommends the use of a 33 to 38 tooth chainring combined
with the standard 22 tooth input sprocket for their gear hubs.
Combining the 33 tooth chainring with the 22 tooth input sprocket
yields a worst case input ratio of 1.5 to 1.
From the conversation I gather that these are recommendations based
on giving the best overall gear inches range for what Shimano
considers normal expected use. I note that on the 8 speed Shimano
hub use of the suggested low would give a gear inches range of 20.5"
to 62.7" when installed in a 26" wheel. This is too low a high gear
I would think for all except the most casual riders.
Even the high recommendation of 22/38 gives a gear inches range of
23.7" to 72.2" with a 26" wheel, still quite low. I would expect an
experienced rider to want a minimum high in the 80" range at least.
My Swobo, with the Sram 9 speed hub is geared about 27" to 92" and
my Civia Rohloff has gearing from 21" to 110". I consider both to
be reasonable gearing for their intended markets and use.
Shimano's recommendations indicate to me that their target audience
for their hubs is the casual rider who is not going to be putting
high levels of torque through the hub mechanism by doing out of the
saddle hill riding or other high torque forms of riding. If I were
using the hub on a bike for an experienced and athletic rider then I
would still suggest an input ratio of 2.0 to 1 or higher for best
hub life expectancy.
It was mentioned that Shimano does also offer a optional 20 tooth
input sprocket for their hubs. Use of this, with the same range of
chainring sizes, would raise the gearing by about 9%, still yielding
a high of under 80" with the largest suggested chainring.