On Thursday, June 13, 2019 at 9:58:14 PM UTC+1, Tom Kunich wrote:
On Wednesday, June 12, 2019 at 9:24:44 AM UTC-7, Frank Krygowski wrote:
On 6/12/2019 1:51 AM, John B. wrote:

Some time ago I posted a question about the possible friction losses
when various "gears" are used. Subsequently I have come across a test
of both chain misalignment and sprocket size friction losses.

The test was done with 53-39 front chain rings and a
11-12-13-14-15-17-19-21-28 cassette. The lowest losses were with the
39/17 combination and the highest with the 53/11. Losses with the
53/11 combination were 3.467 times higher than with the 39/17.
The graph states that it is based on the "optimal shift sequence using
the ring-cog combinations with the lowest frictional losses yet
maintaining an acceptable range of final gear ratios."
https://www.ceramicspeed.com/en/cycl...g-size-report/

The second part of the test shows the friction losses with the chain
aligned and using the various ratios of the cassette and chain rings
above.
The lowest losses were with the 53 tooth chain ring and the highest
with the 39 tooth chain ring in all "gears". In other words the 53/ 11
ratio had ~8.2 watts losses while the 39/11 ration had ~8.5 watts. The
53/28 had ~5.6 watts losses and the 39/28 had ~6.2.

So the test was run with an input power of 250 Watts. Typical losses
were about 7.0 to 7.5 Watts. That gives a typical efficiency of 97%, and
that applies to almost all the various chainring and sprocket
combinations. The 53-11 combination drops the efficiency down to 96.6%,
still not too shabby. It's only the weird combinations like 39-11 that
lose significantly more, and even that comes in at 96% efficient.

The important point, though, is that there doesn't seem to be a more
efficient system. Yes, the efficiency would drop if the chain was
extremely grungy and (I assume) worn. But that's easily fixed.


--
- Frank Krygowski

Why would we even bother to discuss an item such as a chain drive when the total loses at worse case is less than 5%? Andre believes that those multispeed hubs are "more efficient". I would actually have to see the figures on it because heavy grease or an oil bath actually absorbs more energy to move it out the way.

Do I suppose I would agree that in inclement weather the efficiency of the multispeed hub is better the difference is so slight as to be nearly undetectable.

Yah, you're right. But you have to consider the context. I was posting in response to a thread then (and apparently still -- we're in it) current in which fractions of 1% normative (ideal state) difference -- of no possible perceptible concern to real world cyclists -- were held up by the usual suspects as reasons for a whole chorus of hallelujahs. And those were laboratory results, so I made the point that what counts for the cyclist is the actual on-the-road *average* efficiency, where the enclosed hub gearbox, especially with an efficient chain enclosure (I mentioned the Hebie Chainglider with which many known cyclists have had good experience in the years since I first recommended it), clearly starts scoring after some miles. I never said that I was talking about more than a very few per cent. The entire conversation that I was dissing was an example of obsessive compulsive disorder.

However, while I further agree with you that an open grease-less gear cluster, while clean and with a straight chainlink, is more efficient than an enclosed oil bath gear-cluster or one filled with grease, the hub I was holding up as the most efficient, the Rohloff Speed Hub 14, doesn't have anything resembling an oil bath or even grease inside it. It isn't even sealed like an automative gearbox; excess oil just "mists out" and its breather hole is dead centre in the axle, so that excess oil won't stay in it long. All it has, in my application and that of the most knowledgeable users, is 12-14ml of thin oil to cover the gears' mating surfaces. That's good for a year or 5000km/3000, after which the hub is serviced and that oil layer washed off (by a winter thickness oil, even thinner) and renewed. If you're interested in the details, see my article "Power-servicing your Rohloff" at
http://thorncyclesforum.co.uk/index.php?topic=13327

Andre Jute]
Perspective