Understanding cog ratios
#1
Thread Starter
Newbie
Joined: Jul 2022
Posts: 44
Likes: 9
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?
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?
#2
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
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.
#3
Wheelman
Joined: Aug 2021
Posts: 1,649
Likes: 1,632
From: Putney, London UK
Bikes: 1982 Holdsworth Avanti (531), 1961 Holdsworth Cyclone, 1953 Holdsworth Whirlwind
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.
https://www.gear-calculator.com/?GR=...N=MPH&DV=speed
The 'Compare' button at the bottom right lets you compare two setups directly.
#5
It's MY mountain

Joined: Sep 2006
Posts: 10,175
Likes: 4,236
From: Mt.Diablo
Bikes: Klein, Merckx, Trek
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.
#7
Thread Starter
Newbie
Joined: Jul 2022
Posts: 44
Likes: 9
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.
#10
Senior Member


Joined: Oct 2014
Posts: 14,171
Likes: 5,299
From: Portland, OR
Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder
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.)
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.)
#11
It's MY mountain

Joined: Sep 2006
Posts: 10,175
Likes: 4,236
From: Mt.Diablo
Bikes: Klein, Merckx, Trek
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.
#12
Senior Member
Joined: Feb 2009
Posts: 6,660
Likes: 177
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?
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?
#13
Maybe we should all recall this thread: Correct chain length not possible?






