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If I have a bike with the same cranks setup with a 36t (chainring) / 12t (cog) ratio and the same bike setup with a 48t (chainring) / 16t (cog) ratio, would the effort required to maintain a set speed be the same for both setups or is there some small difference created due to the size of the chainrings? This assumes a 3:1 ratio on both cranks.

Would there be a difference in a geared versus single speed (no derailleur, same chainline) configuration?

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    The net-net is that any differences are due to differences in friction, plus going to a fixie you might change the crank extension slightly which could have a tiny ergonomic effect. Any such effects are pretty negligible and hard to predict.
    – Daniel R Hicks
    Dec 9 '14 at 3:05
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Here are some points taken from the literature:

  • Mechanical efficiency is usually 88-98% for majority of deraileur systems (when clean,lubricated and new)
  • Drivetrain efficiency decreases with smaller rear cogs,
  • Highest efficiency can be reached at high torques and low cadence,
  • Chainline effects are negligible, imposible to note with measurement apparatus,
  • Higher efficiency can be obtained with a single-speed as opposed to derailleur use, and there may be a few reasons for this.
  • Efficiency of an internal gear hub is generally lower than this of a derailleur system*

So in your case it's likely that the 48/16 setup will give a slightly higher mechanical efficiency. Also once you've gained the desired speed higher rotational inertia of larger sprockets will help keep the speed at slightly lower effort. On the other hand lighter and smaller sprockets will make it easier to accelerate. However all these changes will be barely noticeable on the road, and especially when the drivetrain is already worn.

Some research has been done in the past on this topic, and there are also pages like this one, where the data on resistive forces within the drivetrain can be bought..

*Reference: Wilson, David G. Bicycling Science 3rd ed. 2003. p. 342-344

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  • Single speed should be more efficient just with the reduced mass of the chain, no?
    – Deleted User
    Dec 9 '14 at 0:08
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    @ChrisinAK - Reducing the mass of the chain has virtually no effect.
    – Daniel R Hicks
    Dec 9 '14 at 3:07
  • Single speed is more efficient because you don't deal with the friction in the jockey wheels / pulleys.
    – Jahaziel
    Dec 9 '14 at 15:18
  • This may be also due to wider chain and sprockets in a single-speed system or lacks of stiffness within the derailleur. I haven't come across any data on these aspects though...
    – Slovakov
    Dec 9 '14 at 20:04
  • Just to add: FrictionFacts have published a report where they actually managed to measure the chainline effects. I haven't seen it, but know it's there and the difference is measurable.
    – Slovakov
    Jun 15 '15 at 10:51
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Chainline would have a (small) effect. If you are cross chaining 36 to 12 then that would not be as efficient and cause more wear.

Geared versus single speed is another question in my mind as a lot changes - type of chain.

Same chainline I doubt the efficiency difference is enough to measure.

On a smaller rear the chain has to take a tighter radius but you also feed less chainline.

In a single speed I would go 48t / 16t and then you can go up or down.

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  • Would there be any difference if the chain-line was identical or Single speed setup?
    – Benzo
    Dec 8 '14 at 19:56
  • My guess would be 48 / 16 would be better as the chain does not pivot as far but I doubt it would be enough to be able to measure. On the other side you are not feeding as much chain. So I just don't know. Most single speeds have a small gears in the rear. Bigger was better I think you would see it more often.
    – paparazzo
    Dec 8 '14 at 20:00
  • The only science I've seen on this suggests that chainline has zero effect on efficiency and that for a given gear ration big/big is more efficient that small/small.
    – Fred the Magic Wonder Dog
    Dec 9 '14 at 4:22
  • @FredtheMagicWonderDog Site the source. That makes no sense. The chain experiences addition friction to deal with any offset in chainline.
    – paparazzo
    Dec 9 '14 at 14:47
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    Only in theory, in practice the angles aren't enough to make a measurable difference. Modern chains are relatively flexible. ihpva.org/HParchive/PDF/hp50-2000.pdf
    – Fred the Magic Wonder Dog
    Dec 9 '14 at 14:57

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