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Given two identical, fixed-gear bicycles, one with a 36/12 gear combination and another with 48/16, will there be any noticeable difference when pedaling these two bicycles? I understand there may be some negligible differences due to differing amounts of chain wrap on the cogs, etc.

I have a friend who alleges that, despite those bikes having identical gear ratios, the 48T chainring will be "better" for a rider preferring a lower cadence and the 36T chainring will be "better" for a rider preferring a higher one. I've attempted to explain to him that this would require the bikes to somehow have differing amounts of development per pedal rotation, which they do not as I have tried to demonstrate here: http://www.gear-calculator.com/?GR=SGLS&KB=36&RZ=12&UF=2240&TF=90&SL=2.6&UN=KMH&GR2=SGLS&KB2=48&RZ2=16&UF2=2240

Please help me win this argument!

  • Of course, the wheel diameter is also a factor. – Daniel R Hicks Sep 25 '17 at 21:38
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    It's impossible to "win" an argument if the other side will on concede to facts or logic. – Rider_X Sep 25 '17 at 22:01
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    What are you trying to win? As long as you both ride, you're both winners. – Criggie Sep 25 '17 at 22:16
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    Back in the dark ages the size of the chain ring was a measure of the cyclist. A bigger chain ring meant you were in all ways better. A real man would learn to mush a big chain ring rather than spin on a small one and admit his inferiority. Ultimately its just phallic thing and the liability of testosterone that logic cannot argue against. – mattnz Sep 25 '17 at 22:51
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    Ask your friend to explain how they'd be different, with numbers and math and physics. – Adam Rice Sep 25 '17 at 23:22
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The gear ratio is exactly the same, the only possible difference is in the efficiency of the power transmission. Big/Big is generally more efficient, so it should be better for both, unless there is some reason that greater power losses in the transmission chain help "spinners".

So they will potentially feel different if you can notice the difference ( pretty small ) in the efficiency of the drive train. I don't see how that translates to masher vs spinner though.

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

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Larger sprockets are slightly more efficient. According to https://www.cyclingpowerlab.com/DrivetrainEfficiency.aspx, you may get 0.5% more effective Watts, which would translate into something like a 0.2% speed gain. At an average of 20kmh, that is 40 meters per hour...

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The claim that Big/Big is more efficient depends on the fact that the links in the chain bend more when going around smaller gears so there is more loss to friction as the links bend. It ignores the fact that you move more chain when using Big/Big. The 48/16 will move 33% more chain through the gears than the 36\12. Each link will move about 3/4 of the angle. Friction on moving is often divided into breakaway and continuous friction. You have the same amount of continuous- half again as much for the 36/12 but 2/3 as often, but only 2/3 as many breakaways. Tiny compared to air resistance.

But the bottom line is that in this model you want small gears, like 36/12.

  • 50% additional chain for the 48 sounds suspiciously high. When I install chain on different size drive chains it usually only varies by a small handful of links. – whatsisname Sep 26 '17 at 5:08
  • @whatsisname: It should be 33%. It doesn't matter how much longer the chain is. You pull that much more chain with a big gear. If you want three revolutions of the rear wheel, in 48/16 you have to pull 48 links of chain while in 36/12 you only pull 36. The ratio of angular movement was also off, updated. The basic idea does not change. – Ross Millikan Sep 26 '17 at 5:18
  • Are you not talking about the total chain length? – whatsisname Sep 26 '17 at 5:30
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    No, I am talking about how many links of chain pass one point. You can think of the top point of the chain ring as the reference. One revolution of the pedals will move 48 links past that point in 48/16 and 36 links past that point in 36/12. That makes the same number of links flex and unflex at each end of the bike. – Ross Millikan Sep 26 '17 at 13:37
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    It's not a claim, there's actual research to support it. – Fred the Magic Wonder Dog Sep 26 '17 at 23:38
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I'd say if the cranks are the same length and the wheels a and tyres are the same size there will be no difference in cadence.

Taking physics into consideration:

  • smaller sprockets mean shorter chain and in total less weight thus less energy needed to cover the distance, however there is more friction on the chain links (power loss) and more tension on the chain so probably stronger chain might be required.
  • larger sprockets mean longer chain thus more weight. But there is less tension and less friction on the chain itself.

Whether the lower friction on the chain compensates for more weight of the drive - I have no idea but I reckon it won't. Whether a stronger chain is needed for smaller sprockets - I doubt as lengthwise the chain is pretty strong. It gets weak from flexing it sideways.

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The efficiency of the system warbles inconsequentially. Bigger gets you less frictional loss per link, but more links and more weight. That aspect comes out in the wash, and if you really want to figure it out conclusively you would need full information on materials, lubricity, etc.

However, the part of this that actually has an impact on function is that bigger gears and more chain wear longer, and so they're more economical and all else equal will be fresh/unworn longer, making them more efficient and less maintenance-intense.

Counterbalancing wear is that some disciplines care a lot about obstacle and/or frame/component clearance Those are the two aspects that lead to the different genres of bike using the sizes they do, wear life versus clearance.

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