On 6/7/2014 4:46 AM, Sir Ridesalot wrote:
Back in the days of 10 gears bicycles it was recommended due to chain deflection
and duplicate gears that you not use the big big or small small
combinations of cog
and chainring. How many cogs-chainring combos is it recommended to not
use on 9 speeds,
10 speeds and 11 speeds rear clusters?

First, I don't think the advice against big-big and small-small combos
had much to do with duplicate gears. I think the main idea was to
protect the chain from excessive lateral bending, which would probably
induce more friction loss at the side plates. IOW, less efficiency.

But modern chains are more flexible than those of the 10 speed days (the
1970s), so I think that's much less of a worry. Generally, the penalty
for angling the chain is minor.

There may be exceptions. My touring bike still has "half-step + granny"
chainrings (something like 52 - 47 - 24 teeth). Putting it in the
small-small gear has the chain almost scraping the side of the 47 tooth
ring. I suppose on some bikes, you might get interference there
(although nobody needs half-step+granny with 9 cogs). And as Duane said,
on some bikes you might run out of chain or run out of derailleur capacity.

Absent such obvious problems, I don't worry about it much. With 9 cogs,
you can get any reasonable gear with a pretty straight chain line; but
IME if you have the chain bent a bit further, it does no real harm.

--
- Frank Krygowski