Chain ring sizing
 

I may have posted here that last year I had terrible grinding
slippage of the chain on my tandem when standing and really
hitting it (climbing or trying to quickly get across an
intersection from a dead stop). The sound was different from a
chain slip that comes from worn chain/cogs.

After a lot of investigation, I finally tracked it down to a 38
tooth middle chain ring (that had been paired with a 50 large).
The 50 was specced for a 39 minimum middle--my recollection is I
went with a 38 because I had a 26 small and had read one should
not have greater than a 12 tooth difference between rings.

The final observation that confirmed this, was small wear marks on
the tip of each spider arm--indicating that the chain had been
hitting on the sider ends, and not fully seating on the ring.

I changed to a 39 middle, and the problem was completely fixed.
On top of that, shifting down to the small ring is *more* reliable
now. I surely didn't expect that, but am pleased.

For what it's worth, I run Shimano components--except for the
front brifter, which is from an older Campy triple. The extra
granularity in derailer position is something I like.

--
Ted Heise West Lafayette, IN, USA