On 3/19/2019 6:32 AM, John B. Slocomb wrote:

Last Sunday I was on my usual weekly "long ride" (which was hardly as
long as it used to be). And I was sort of looking down and the chain
was on the big chain ring and the 5th cassette sprocket (9 speed
cassette) and I got to thinking.

Note the friction losses for a chain drive are usually considered to
be very low, the usual efficiency of a chain drive is usually reckoned
to be "up to" 98%. But the instructions for installing a chain drive
is always to ensure that the drive and driven sprockets are exactly in
line.

But the conventional bicycle with it's multiple front and rear
sprockets does not have the sprockets aligned except in two instances,
assuming the usual chain line dimensions. When on the large front
chain ring and (usually) the center cassette sprocket on an uneven
numbered cassette, and when on the small front chain ring and a larger
cassette sprocket. Perhaps two sprockets larger than center.

So, if the usually chain efficiency figures are used the chain is
delivering the 98%+ efficiency only twice in a possible 18 speed
range.

What efficiency is being delivered during the periods when the chain
is not perfectly aligned?

And should one worry about it?


Classic chain is roller chain and yes those run dramatically
worse when chainline is askew. But after Sedisport, modern
derailleur chain has interrupted sideplates with no full
roller so they are quite forgiving of misalignment or,
viewed another way, better shifting on derailleur systems.
One downside is much faster wear but since they are
relatively cheaper to make, we just throw them out sooner.

I don't know the numbers for efficiency of derailleur chain
at various angles but I think you're right although it may
well be a reasonable tradeoff for other features.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971