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Old June 13th 19, 10:12 AM posted to rec.bicycles.tech
Andre Jute[_2_]
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Default How efficient are derailleur bicycle transmissions really?

On Tuesday, June 11, 2019 at 10:20:06 AM UTC+1, Andre Jute wrote:
A figure currently thrown about on with abandon on the newsgroup is that bicycle chains and sprockets are 98% efficient. That isn't untrue in certain very limited circumstance, but the minute you ride that bike to which those limited circumstance apply beyond the bottom of your drive, the efficiency falls and undermines the 98% assumption.

The 98% assumption *requires* a single-gear or fix bike with a dead straight chainline, sprockets and chain rubbed in to each other (not new, off the shelf) but not worn beyond the point of lowest friction either, and all parts to be dead clean and lubricated to perfection.

Any cyclist with his brains in gear knows this case doesn't perpetuate itself once you're out of the garage. The lube attracts filth to itself and the efficiency heads south.

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So you have to cover that chain, not a perfect answer but one that with modern materials and design is possible without a huge further downgrading of efficiency by either additional weight or friction. I have in mind here the Hebie Chainglider which just about totally encloses your chain. I have about 30K miles of experience with various chain covers in a deliberate longterm experiment, and the only one I will recommend is the Chainglider. Anything else lets in dirt, and there goes the efficiency.

But you can't fit a good enclosure about a derailleur transmission. Oops.

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If you're going to be forced to operate a single-gear bike anyway to preserve average efficiency, you may as well use a hub gearbox, which to the gestalt of the bike appears like a single-gear system, and works with the virtually no-cost (in efficiency terms) Chainglider.

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A little, a very little thought* will persuade you that the efficiency of an open-chain single-speed bike, or a derailleur bike, inevitably goes downhill from the moment it is first used, while the hub gearbox efficiency increases as it is run-in and then remains largely stable for most of its lifespan (in a Rohloff unknown, but assumed by reference to the experience of world circumnavigators to be north of 200,000km, in a Shimano 8sp Nexus Premium said to be 50,000km).

On average for any ride or for its total life, a hub gearbox, especially if the chain is suitably covered, is likely to be more efficient than a derailleur system or a fixie.

I will bet that my Rohloff hub gearbox equipped bike (perfect chainlink, chain running for its entire life on the factory lube, stainless steel sprockets, chain totally enclosed in Chainglider) in your garage is as efficient as your brand-new derailleur bike, and five miles from your house is more efficient than your brand-new single gear/fixie as well.

It is the gradual recognition of these facts that drive more and more road-cyclists to fit hub gearboxes to their winter training bikes.

Copyright © 2019 Andre Jute
*A little, a very little though will suffice -- John Maynard Keynes


A quick way of summarising all this is:
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What really matters is not the efficiency of any transmission in the laboratory, but the average efficiency on the road in normal rides.
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On those parameters, a Rohloff leaves a high-quality derailleur for dead within a few miles and even a lesser quality hub gearbox will on average prove more efficient within a few miles more.

On these parameters -- average efficiency on a real world ride -- it is not even worth discussing any available transmission except derailleur with chain. and hub gearbox with chain or Gates belt drive. Shaft drives and whatever else cannot touch them.

Andre Jute
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