53 X 16 vs. 50 X 15 gearing

Bicycling magazine had an article on Shimano when they first hit the
scene with SIS and small cogs (12T in this case). Apparently they had
a guy working full time to optimize the cog because small cogs are less
round. I guess that's the pitch thing mentioned earlier. anyway this
made for less efficient pedaling.

sorry no reference to the article. but it was probably 1983-84-85 or
thereabouts.


--
carpediemracing

Smaller cogs are actually more efficient.

One aspect of this that is often overlooked is the effect of chain
tension on efficiency... ie increasing the chain tension improves the
chain efficiency... and smaller gears have higher tension (at the same
riding speed and power output) than larger ones. It is true that a 15
tooth sprocket is more efficient than an 11, provided that the power
input and front ring size is the same in both cases; unfortunately that
isn't the right comparison to make. If we want to travel at a
particular speed with a particular cadence, then we have to change the
front ring size by the same proportion... and the chain tension will
change by the same amount. A 53/15 is the same gear ratio as a 39/11.
This is the kind of comparison that needs to be made. Spicer's testing:
http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf
showed that chain tension is actually more important than spocket
size... though he failed to note this in his conclusions. But Walton
noticed, and published the results he
http://www.ihpva.org/HParchive/PDF/hp51-2001.pdf
When you compare the effect of sprocket size while keeping riding speed
and power output constant, the smaller sprockets are most efficient...
especially at lower power outputs. At higher power the results
converge.

So... I wouldn't worry about losing efficiency with the small
sprockets.

Some of the other interesting conclusions from Spicer's testing:

1) Cross-chaining has a negligible effect on efficiency.
2) Lubrication doesn't matter (in the lab at least).
3) Friction can account for only a few percent of the overall losses.

That last one is especially noteworthy... If friction doesn't account
for the losses, then what does? Vibration?