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.

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/

The figure 8 graph is where your power is being applied. The pinched points are the dead spots in your stroke. With concentration, you can achieve a much more linear application, as is shown in the second graph. However, this was on a trainer, indoors. Most riders,even good competitive amateurs, can't achieve pedaling efficiency on the road without good training and coaching.

To be more succinct, any losses due to misalignment are not only negligible, but nearly moot until the rider can achieve the most bio mechanically efficient pedal stroke, and even then it won't make a helluva lot of difference.

This is why riding a fixed gear bike is more efficient - the lack of the freewheel and tension spring force a more effective pedal stroke - it smooths you out. Once the rider can develop a smooth power curve, a fixed gear becomes eve more efficient.

And no, before anyone starts prattling on, we are _NOT_ talking about getting more out of the system than you put in (oh no, he's talking about perpetual motion machines!!!) it's purely a less lossy system. You get more _OF_ what you put in, NOT more _THAN_ you put in.

Biomechanical efficiency is the real point here. This is why it's better to be able to shift to an easier gear on the climbs - It keeps the _rider_ in an efficient pedaling zone. The rider biomechanical efficiency is significantly more important than the mechanical losses in the system.

I know, I know...there are people in this forum who have a pedal stroke so efficient that the losses from the freehub and sprung chain are irrelevant. Sure. Whatever helps you sleep at night.

In reality, the most noticeable effect of misalignment is chain wear.