One thing that doesn't seem to be have discussed :
- What effect does using a worn chain sprocket, chainring have on the transmission efficiency ? To me, a new chain and sprocket "feels" more efficient than a worn transmission, but some of that is probably psychological.
A smart move when one suspects that the desired data point would be too small to measure accurately, is to find either an analogue, or some way to alter the relationship by a few factors, often by applying the cause to the full length of the whole rather than some fraction of it, so that you measure a size easily picked up by available instruments and your answer is simply the result of a division.
A bit of lateral thinking gives us a full length to work with: When the chain has broken off enough teeth on a very worn sprocket so that the chain can no longer engage the sprocket to pull it around, the transmission has been 100 percent degraded to zero percent efficiency.
If we take that obvious condition of the transmission with another obvious but related condition, say when the bike was brand new, unridden, we can calculate the extra mileage that a component gives us, say a different chain, or a Chainglider. That can then be taken as an unrealized efficiency. For instance, the Chainglider multiplied the chain life on my bikes between three and four times. Let's work with a factor of three. That's a clear gain of 200 percent. QED: it becomes easy to understand why I'm so enthusiastic about the Chainglider.
Because I threw off what has now become clear are considered halfworn chains by some on this forum, that already deeply impressive efficiency gain is only half the potential gain at 1 percent chain elongation. So now we're up to 400 percent potential gain.
I suspect that's still not all the potential, because the sprockets in the photos in this thread were very likely taken when chains had been abused well beyond 1 percent elongation. But we don't have any further data.
Neglecting different efficiencies from different chain lubes, ... ... ...
[GEORGE, HAVING QUOTED MARTIN, OFFERS AN IMPRESSIVE ANALYSIS OF HOW VARIOUS FORMS OF TRANSMISSION WEAR, EACH SMALL ENOUGH TO REQUIRE SPECIALIST EQUIPMENT AND METHODS TO MEASURE, MAY OR MAY NOT ADD UP TO SOMETHING SIGNIFICANT.]
With the proponents on this forum for chain gliders, that is additional friction.
There's bound to be a minimum level of friction in any transmission system where metal rubs on metal, or hydraulic fluids move masses or resist their movements.
I'm not so much fascinated by that practically irreducible friction which is the unavoidable overhead of any chain or belt drive system. One of the benefits of the Chainglider is that it permits us to eliminate a lot of guesswork because the Chainglider by the very nature of its effective enclosure sums together such fraction of each of these fractions of a percent as can reasonably or even unreasonably, right out at the furthest frontier of rationality, be expected to be eliminated. This I'm willing to take as the point where a further reduction of one percent of an, already fractional, amount of friction will cost not ten percent but hundred percent more effort, time and money, in short where we enter the region of irrational obsession and absurdity.
In the common game of comparing derailleur efficiencies with those of hub gearboxes, there's a bedeviling factor: The derailleur transmission in a real life comparison on the roads is not statically efficient: it declines dynamically from perfectly clean and tuned at the outset of the test as the chain and gears pick up dirt. An open Gates type belt drive ditto, to a presumed lesser extent than the derailleur. A fixie or hub gear chain under a Chainglider would come closer to a steady state efficiency, altered only, as you imply in your post above, in a minimal way, from the qualities of the lube used on the chain. I don't think a meaningful measurement of the difference can be taken under a thousand miles, and in real life I wouldn't sanction any expenditure on measuring something we can do nothing
further about.
Bottom line, I often leave my dyno powered lights on in daytime, even when I am on a bike trail where there are no cars to worry about because I can't feel the extra lost wattage from that, so I don't worry about it. That is several extra watts lost, probably a bigger loss than the extra friction at the worn drive train.
I do the same (because before I gave up the car altogether, we had a Volvo Estate to run the child safely to school, and I was impressed by its daylight running lights), but I'm not at all certain that the loss is 'several' watts. Modern hub dynamos are really very efficient and low friction, say compared to a generation earlier, where it was repeatedly found that one Shimano hub dynamo consumed less power when it was switched on than when it was switched off! Also, even modern hub dynos are design iterations from their ancestors, and are not yet fully acclimatized to the now-standard LED lamps which fully replaced filament bulbs less than twenty years ago. As a consequence, bicycle hub dynos have power to spare: It wouldn't surprise me to hear they're the most efficient active component, including the human, on every bike fitted with a modern hub generator. I wouldn't expect you to notice anything from the hub dynamo, except that it makes light and charges the phone on demand.
