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Understanding cog ratios

Old 08-03-22, 01:57 AM
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bikethis
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Understanding cog ratios

Hi guys,

I currently have a setup with a 42T front chainring and a 14T rear sprocket. I really like the resistance this gives me for riding around my area, however, I am wondering this:

If I switch to an 11T rear sprocket and 33T front chainring, this will give me the exact same ratio but will it give me the exqact same pedalling experience on the bike?

What would I be losing by making this change? Surely there has to be something?
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Old 08-03-22, 04:01 AM
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alcjphil
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11 tooth cogs wear out much faster than 14 tooth cogs
They also are not as smooth https://chain-guide.com/basics/2-2-1-chordal-action.html

Last edited by alcjphil; 08-03-22 at 04:08 AM.
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Old 08-03-22, 04:06 AM
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Aardwolf
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I've found Gear Calculator good for comparing cogs:

https://www.gear-calculator.com/?GR=...N=MPH&DV=speed

The 'Compare' button at the bottom right lets you compare two setups directly.
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Old 08-03-22, 04:56 AM
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BTinNYC
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What alcjphil said. The bigger sized gearing will be smoother
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Old 08-03-22, 08:12 AM
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Originally Posted by bikethis View Post
If I switch to an 11T rear sprocket and 33T front chainring, this will give me the exact same ratio but will it give me the exact same pedalling experience on the bike?

What would I be losing by making this change? Surely there has to be something?
Switching from a 42t to a 33t probably means switching to a triple crank - some people like them and some don't... but it'll be different.
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Old 08-03-22, 08:16 AM
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GhostRider62
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A 54 x 18 is more macho, a 33 x 11 is a bit weenie aside from wearing out faster and adding more friction
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Old 08-03-22, 08:39 AM
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Originally Posted by DiabloScott View Post
Switching from a 42t to a 33t probably means switching to a triple crank - some people like them and some don't... but it'll be different.
Can you explain why please? I have a 34T chainring that I used to run on this bike and it worked fine apart from being too easy to pedal.
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Old 08-03-22, 08:40 AM
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Originally Posted by GhostRider62 View Post
A 54 x 18 is more macho, a 33 x 11 is a bit weenie aside from wearing out faster and adding more friction
Unfortunately my frame won't allow for anything larger than a 42T.
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Old 08-03-22, 09:27 AM
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Post #2 answered your question perfectly. What more do you want to know?
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Old 08-03-22, 10:08 AM
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Originally Posted by bikethis View Post
Unfortunately my frame won't allow for anything larger than a 42T.
Tell us what your bike is and what crankset you are using and we might be able to help you more. (Not being able to use bigger than 42 teeth? It's an unusual bike that won't allow bigger with a standard crankset if it as a regular road bike that takes 27" or 700c wheels. Most single speed and fix gear bikes and wheels are designed to use a chainline a set distance from the center of the seat tube. (42mm if I recall correctly.) That chainline virtually always allows as big a chainring you you can get.

Chainlines - they should be straight for SS and fix gear. You should be able to sight up the chain from the rear and see no "S" turn to it. If your bike is a conversion from a double or triple, it may well be that the small chainrings are inside that proper chainline and not aligned with the rear cog. (Knowing nothing of your bike or setup, this is all speculation. But Diablo Scott's comments may well be on the widths of various types of cranksets pressed into single speed duty.)
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Old 08-03-22, 02:38 PM
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Originally Posted by bikethis View Post
Can you explain why please? I have a 34T chainring that I used to run on this bike and it worked fine apart from being too easy to pedal.
34t is about as small as most double chainrings go - it has to do with standard dimensions in the crank to mount the rings - called the "bolt circle diameter"
33t requires a different BCD - like the kind that triples come with.
You almost certainly cannot swap the 34 you have now with a 33... you might be able to find a whole new "sub-compact" double crank that has a smaller ring.
So it's just an availability issue.
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Old 08-03-22, 03:09 PM
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Originally Posted by bikethis View Post
Hi guys,

I currently have a setup with a 42T front chainring and a 14T rear sprocket. I really like the resistance this gives me for riding around my area, however, I am wondering this:

If I switch to an 11T rear sprocket and 33T front chainring, this will give me the exact same ratio but will it give me the exqact same pedalling experience on the bike?

What would I be losing by making this change? Surely there has to be something?
The smaller cog won't be as efficient.
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Old 08-03-22, 04:35 PM
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alcjphil
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Maybe we should all recall this thread: Correct chain length not possible?
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Old 08-03-22, 09:41 PM
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^^^This.

OP is in a "throw parts at it and see what sticks" phase of his project
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