fooferdoggie 

this is on a standard Shimano 10 speed 11-32 cassette 10 speed. the 11 is just to small on our tandem we have to go 22mph or so to spin at 80 rpm and we cant manage that unless on a slope. a 12 should work better. I have this guy

SoSmellyAir

Shimano cassettes are designed with shift ramps aligned and coordinated between adjacent cogs, so changing just one cog may lead to poor shifting performance, including skipping the second smallest cog altogether. Additionally, the 12T cog shown in your photo does not appear to be one designed to be the outermost cog with an interface with the cassette lock ring. Best you switch to a 12-30 cassette.

tFUnK

I've done this on multiple cassettes but as mentioned you want a 12t terminal cog to work best with the lockring. The other thing is a lot of cassettes go 11-12 so now if you're starting with 12 where are you going to add the extra cog? I guess if it's a large range cassette that starts 11-13 then you'll have a 12-13 which will be fine. When I replaced mine I went from 11-17 to 12-17 (trade the 11t for the 16t), and the best way I've found is to use a 12-25 or 27 cassette and just replace the whole 11-17 with the 12-17. If you're going to replace individual cogs to add the 12t and 16t cogs, you might run into suboptimal shifting from the 16t to the 15 and 17 cogs that were designed to be next to each other.

Bill Kapaun

I wouldn't worry about shift ramps etc. on the end cog.
A 12 T cog from a 9 speed would also work, since the chain isn't constrained by cogs on both sides.

Maybe just buy a new 12-30 if a 30T largest cog will work?

fooferdoggie 

well the 9 speed is easy. I have had to bu ya supply of 13t cogs they only last maybe 2000 miles since we ride in that cog most of the time.
https://www.ebay.com/itm/22486400540...Bk9SR-rdkPH9YQ

tFUnK

Is your current cassette 11-12-13-15-17-19-21-24-28-32? If you take out the 11 and 12 and replace with a terminal 12t, what other cog will you add?

rm -rf

The smallest cog needs to have the knurled surface to work with the lockring. So the 12 you pictured wouldn't work as the smallest cog.
~~~



~~
Sram has a 10 speed PG-1050 in 12-32:
12 13 14 15 17 19 22 25 28 32
compared to Shimano 11-32:
11 12 14 16 18 20 22 25 28 32

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I don't know what chainrings you have. So I used the typical 34/50 for a road bike:
From the useful Mike Sherman's Gear Calculator. This chart shows speeds in each gear combination for the selected cadence range. Large chainring in black, small chainring in red.

Shimano 11-32 at flat road cadences.
There are close shifts toward the low end, largest cogs. This still works okay in the small chainring, since cross-chaining the two smallest cogs is usually avoided.



~~~
Sram 12-32.
It has nicely spaced shifts in the 10 mph to 16 mph range -- useful.
The 12-13-14-15 with a 50 tooth chainring is up in the 20+ mph range, though.



~~~~~~~~~~~~~~~~~~~~~~~~~~
11 tooth cog
I used to think that the 11 cog was just "marketing".
But: one advantage of having the 11 tooth:
You can cross chain your small chainring to the 13 cog. (avoiding the two smallest cogs when cross chained.) But this assumes the cassette starts 11,12,13,14... That's typical in 11-speed, but not in 10 speed. So it doesn't really apply to your situation. Both the 11-32 and 12-23 have a 14 as the third cog.

For example:
34-13 at 90 rpm is 18.1 mph
34-14 at 90 rpm is 16.8 mph.
A larger speed range without shifting the front derailleur -- good.

Hondo6

As others have said, it's best to use an outermost cog with the built-in serrations that help the lockring lock tightly.

And if I remember correctly, you'll also need a new lockring. Unless Shimano's changed the design, I don't think a lockring designed for an 11T outer cog works particularly well - if it works at all - with a larger outer cog.

Crankycrank

As far as needing a dedicated outer cog with the serrations, I have run two different cassettes in the past using the second position cog like the OP wants to do and had no issues for around 15k miles each. The lockring will come loose a little easier without the serrations if not tightened properly but using the standard torque will be fine. Also using a non-matched/series cog for the cassette can have varying degrees of shifting sloppiness from no difference to some annoying hesitation when shifting IME.

fooferdoggie 

its 11-42 I forgot I changed it. its 11-13 so I want 12-13
found one

SoSmellyAir

Even 10-speed Shimano 11-32 is 11T to 13T, so a 12T end cog is worth a shot. At most shifting is bad and you have to switch back to the 11T.

KCT1986

The other thing that may affect the swap is how the 13T sprocket is designed. The 13T sprocket for use with a 11T is usually different from a 13T sprocket for a 12T.

A 11T sprocket usually has a thicker integrated spacer that 'nests' part way into the 2nd sprocket, and this will affect the spacing between the sprockets.

Notice in the pics the difference in the shape of the sprockets face in the area where the smallest sprocket would sit. The 13T sprocket for a 12T 2nd sprocket is flat. The 13T sprocket for a 11T sprocket has a recessed ring where the thicker spacer would sit.
13T for 12T sprocket

13T for 11T sprocket

fooferdoggie 

ya its not like we use it all the time. we have our tandem geared to climb not for speed.

KerryIrons

[QUOTE=fooferdoggie;22881468]the 11 is just to small on our tandem we have to go 22mph or so to spin at 80 rpm and we cant manage that unless on a slope. /QUOTE]

I'm confused. a 39/11 at 80 rpm is 22 mph. Do you really have a 39t large chain ring? I agree that you probably don't need an 11 as does hardly anybody. But I don't understand your gearing.

fooferdoggie 

[QUOTE=KerryIrons;22882713]I dont know what the chainring is the drivetrain had to be rebuilt after a crash and I did not see what the mechanic used. I bet its a 40t. it works well for us though anything faster then 22 to 24 and we just coast.

jnbrown

You need a different lock ring that fits 12T

fooferdoggie 

ok amazon fixed that.

urbanknight

Back in the day we did stuff like that all the time to comply with junior gear restrictions. It generally worked well enough.

fooferdoggie 

I finally got both the parts needed. but I cant get it to shift into the 12th cog. I have a through axle and I had a hard time getting on the wheel. the cog is too wide. or I should say it dies no sit down in the 13t cog like the 11t does. I could mill it down but it just not worth all the fiddling and time.

SoSmellyAir

Because ... see post #12 by KCT1986.

fooferdoggie 

but getting that gear may cause issues since its 9 speed? so really the best solution would be to go to 9 speed overall? not really worth something we dont use often.

Bill Kapaun

Belt sander?

SoSmellyAir

Your first post mentions a 10-speed 11-32 cassette, so I am not sure why you are now asking about a 9 speed cog.

Other than not really ever needing the 11T cog, what else do you dislike about your 10-speed 11-32 cassette? Are you looking for tighter gear ratios, e.g., 10-speed 12-28 or 12-30?

Iride01 

On most cassettes I've seen that start out with a 11 cog, a 12 cog is the next lower gear on the cassette. So what do you have that doesn't have a 12 as the very next cog, or what are you trying to accomplish by having two 12 cogs?

A CS-6700 comes in different versions. One with a 12 cog as the smallest from the get go, and no hoping it works.