On 20/3/19 1:16 am, wrote:
On Tuesday, March 19, 2019 at 7:32:42 AM UTC-4, 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?


-- Cheers, John B.

The short answer is no.

The long answer is:

The efficiency due to misalignment in a derrailleur/freehub system is
negligible, here's why:

1. The 98% efficiency you mentioned is in fixed systems with a drive
providing constant smooth torque.

2. Once a freehub system is installed (like a single-speed (NOT fixed
gear)), the efficiency depends almost entirely on the the
bio-mechanical pedaling efficiency. In other words, if you don't
apply even power throughout the pedal stroke, the efficiency of the
entire system drops off dramatically, at this point, losses due to
chain misalignment are barely measurable, let alone being perceptible
by the rider.

I believe John is focused on the efficiency of the chain drive system
alone, not the biomechanical efficiency of the person plus the chain.


3. Make matters worse by introducing a spring tension system. Now in
addition to the bio mechanical inefficiencies, you're adding the
ability of the chain drive to take up slack in the system, which
allows _you_ to pedal even more inefficiently.

Here's a graphic representation:

https://hanswinter.wordpress.com/200...your-spinscan/

I think that, and the rest of your post is complete ********.

--
JS