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So I know that there is overlap between the chainrings and the cassette that yield the same gear ratios ie 30/12 42/17 52/21. Is there any difference in input required for these 3 pairings?
 

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The 52/21 is the best.

Although they have the same ratio, the use of a larger crank and a larger cog is more mechanically efficient due to a smoother rotation and less frictional losses.
 

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M-theory said:
The 52/21 is the best.

Although they have the same ratio, the use of a larger crank and a larger cog is more mechanically efficient due to a smoother rotation and less frictional losses.
I'm no expert (so hopefully one will come along and answer this), but I would think the opposite would be true... small/ small yields lower friction, making the 42/17 the best combo.
 

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Science vs. thinking

PJ352 said:
I'm no expert (so hopefully one will come along and answer this), but I would think the opposite would be true... small/ small yields lower friction, making the 42/17 the best combo.
Since any mechanical engineer will tell you that you will get less friction with larger cog diameter (all else equal), why would you "think" that the opposite would be true? Inquiring minds want to know :)
 

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Kerry Irons said:
Since any mechanical engineer will tell you that you will get less friction with larger cog diameter (all else equal), why would you "think" that the opposite would be true? Inquiring minds want to know :)
(My) logic dictates that less friction would occur where there is less interaction between (in this case) chain, rings and cogs. Simple as that.

Assuming you were referring to your own inquiring mind, hopefully that'll satisfy it. :D
 

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PJ352 said:
(My) logic dictates that less friction would occur where there is less interaction between (in this case) chain, rings and cogs. Simple as that.

Assuming you were referring to your own inquiring mind, hopefully that'll satisfy it. :D
Logical, but incomplete. Most of the friction in that system occurs within the chain, where moving parts with simple sliding bearing surfaces turn over over one another each time a link joint goes from straight to curved, or the reverse, hundreds of times a minute. And the smaller rings mean tighter turns and a higher degree of rotation for all those turns.
 

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What about chainline? I think the 42-17 would be more straight.

Also, this difference in friction, is it an amount that would be measurable in practical terms, or is this in gnat's-ass precision?
 

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JCavilia said:
Logical, but incomplete. Most of the friction in that system occurs within the chain, where moving parts with simple sliding bearing surfaces turn over over one another each time a link joint goes from straight to curved, or the reverse, hundreds of times a minute. And the smaller rings mean tighter turns and a higher degree of rotation for all those turns.
I'm not arguing the point that I'm right, merely explaining my logic.

Good point about where most of the friction occurs (chain), but I see that as a constant, no matter what gear ratios are chosen.
 

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Chain line has nothing to do with how many teeth you decide on.

And really, if someone can actually feel the friction difference between a 52/21 and a 42/17, I'd be shocked.

In my opinion, it doesn't matter.
 

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frpax said:
Chain line has nothing to do with how many teeth you decide on.

And really, if someone can actually feel the friction difference between a 52/21 and a 42/17, I'd be shocked.

In my opinion, it doesn't matter.
With comments like that, parish the thought of ever becoming a mechanical engineer. :)
 

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Diocese?

PJ352 said:
With comments like that, parish the thought of ever becoming a mechanical engineer.
Which parish are you talking about? St. Michaels, St. Mary's, St. Francis? Perish the thought we should end up in the wrong parish :)
 

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Kerry Irons said:
Which parish are you talking about? St. Michaels, St. Mary's, St. Francis? Perish the thought we should end up in the wrong parish :)
... and the irony is that I spent 10.5 years in parochial schools! :eek:

'Pew'! :D
 

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PJ352 said:
With comments like that, parish the thought of ever becoming a mechanical engineer. :)
That was never even a possibility with me. I'm more "creative"... musician, arts, etc. Mathematics and I never seemed to get along.
 
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