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Switch 11T Sprocket To 12T Shimano 8 Sp

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Switch 11T Sprocket To 12T Shimano 8 Sp

Old 01-03-20, 01:36 PM
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Switch 11T Sprocket To 12T Shimano 8 Sp

I haven't had to make any mods on a Shimano cassette in almost 10 years. I did a bunch of web searches and didn't find any answers on Shimano small sprocket dimensions.

ThermionicScott, CliffordK

You guys have posted a lot about changing Shimano sprockets, maybe you can answer my question?

I'm finishing up a new build and I want to change the small sprocket on a NOS Shimano CS-M737-1 11-30T 8 speed cassette from 11T to 12T.

I have NO NEED for a 118" high gear.

I'll be running 48-34T chainrings and new Dia-Compe ENE ratchet levers with a 9 speed KMC chain so no indexing.

The 11T on the NOS cassette is 5.5mm wide/thick. I have some NOS 12T sprockets that are 4.5mm and 5mm wide. Is there a chart or listing of Shimano small sprocket widths???

The 11 speed lockrings are ~35+mm and the 12mm and up lockrings are ~38+mm. I'm all set there. Also I have a 1.1mm thick spacer that I could use with the 4.5mm 12T sprocket.

Any problems with using the 5.5mm 12T sprocket? I'll rarely be using it and the 12T should run a little smoother that the 11T one.

BTW, the Dia-Compe ENE levers have a smoother ratchet mechanism that the old Suntour Power shifters but are nowhere near as robust in construction.

The barrels are 20mm with a special design feature that allow them to work with 9 -10 -11 speed RDs.

Things aren't always what they seem... Don't believe everything you think!

Chas. ;-)

Last edited by verktyg; 01-03-20 at 01:39 PM.
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Old 01-03-20, 02:47 PM
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Is this uniglide (screw on outer sprockets) or hyperglide (outer sprockets + lock ring)? 7-speed?

This is my favorite page on sprocket pitch, cable pull, etc. Sheldon Brown also has much of the info, but on separate pages.


So, assuming hyperglide, there are supposed to be differences between 11T and 12T lock rings, but I'm not quite sure what they are.

I'm doubting your sprocket pitch (total sprocket to sprocket distance) for a cassette will be greater than 5.0mm.

The design of most current derailleurs is to have a little side-to-side slop, so a single sprocket being off by 1/2mm is probably OK. But, you'll run into differences if that difference is compounded over several sprockets. .5 + .5 + .5 + .5 = 2mm...

There may or may not be a slight shifting hesitation due to the sprockets not being indexed properly. But, that may not make a difference either.

Anyway, try your setup out, and you should be happy with it.

Make sure the whole cassette isn't loose on the freehub. If it is, add a spacer behind the stack.
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Old 01-03-20, 03:15 PM
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You should look at the exploded diagrams, which are easily found on the Shimano documents website. Here is your cassette:
It seems to be an old model that uses a lock ring spacer, which I have never used before and don't know it's purpose.

Here is an old model CS-HG50-8 which has the same lock ring spacer design.
You can look up the part number for the 12T 1st position cog, which is Y-11F1219E or Y-11F1223E. $10-11

You have to make sure that the 2nd position cog is designed for the 2nd position with the built in spacer.

The old CS-HG50-8 with the lock ring spacer uses the same lock ring for both 12T and 13T. The part number is y-11F01000. $3.

I don't know if the lock ring spacer is any different, although the one for your cassette has a different part number.. For the CS-HG50-8 with 12 or 13T, the part number is Y-11W02000. $2.

Here is the drawing for the current model of CS-HG50-8 without lock ring spacers.
The 12T first position appears to have the same part number as the old model.
It also has the same 12 or 13T lockring as the old model.
So in the end, I don't know what the purpose of that lock ring spacer is. So assuming that you don't need that lock ring spacer, then all you would need is Y11F01000 and one of either Y11F1219E or Y11F1223E

But then for $17, you could just buy the whole cassette. Sometimes, the cogs mixed from different sets don't shift at all. So if you had the whole cassette, you could swap the 12, 13, 15, 17 cogs in various combinations between the new and old cassette to see which ones are able to shift. For example you could start by putting on the new 12, 13, 15, 17. If 17-20 doesn't shift, replace the 17 with your old cog. Then if 15-17, doesn't shift, replace the 15 with your old cog. If 13-15 doesn't shift, then replace 13 with your old cog.

And then if you want to have a 13T first position cog, you could buy the 13-26T and replace the 13, 14, 15, 17 on your existing cassette. The 17 could also come from your old cassette, you just have to switch them and experiment which one gives you the best shift.

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Old 01-03-20, 03:48 PM
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Spacing on the smallest sprocket usually matters very little except for matters of chain/cog clearance since the RD just rests on the limit screw, but there does need to be enough clearance for the chain and cassette to fit. Usually the reason 11T cogs are thicker is because the 12/13T sitting underneath is recessed to allow the 11T splines to engage the freehub even when the cog partially overhangs the freehub. There generally won't be room for additional spacers because they must have a small enough diameter to fit within the recess in the 2nd cog. There is indeed a difference between 11T and 12T lockrings, as would be expected, the 11T one is smaller, and designed to interface with the ridges on an 11T, but won't interface well with the recess on a 12/13T. For many cassettes, the 12T 2nd cog is identical to a 12T end cog, however, it is often designed with a flat sheetmetal cog behind it, not a recessed cog. A cassette with an 11-13-XX progression often has a 13T that is recessed to allow room for the extended 11T splines. A 12-13-XX progression sometimes expects a 13T cog with a flat face and without a recess. The extended splines on the smallest cog, and the recess on the the 2nd cog, and all the little variations between various cassettes are what make swapping them tricky. There are multiple things to consider. Whether a spacer would fit in the recess, whether the 12T sinks into the recess, whether the 11T lockring sits in the 12T recess and bottoms out. Things might work out with the parts you already have, but on the small end of the cassette it's often a bit more complicated than just cog thickness and spacers.
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Old 01-03-20, 04:25 PM
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Lots of good points, above^^^^^

Shimano's Dura-Ace Uniglide freehubs with reduced threading diameter were made to accomodate 11t cogs, but all the others including early HG ones (and D-A 8s HG) were not made to accomodate 11t cogs, since there wasn't enough metal left on the cog for sufficient strength.

So when 11t cogs appeared on MTB hubs made for "compact" drivetrains, an afterthought solution was to shorten the spline's length enough to create a sort of reinforcing ring integral with the 11t cog. This changed the dimensions of the cog and also meant it wouldn't fit on an HG hub having the previous full-length splines (but which could still be shortened the necessary 1-2mm using a grinding wheel).

Going in the other direction (putting a 12t cog onto a more-contemporary compact-style freehub body) presents no problems because these later hubs are 11t and 12t compatible. By 1997, all Shimano freehubs would be 11/12t-compatible.

So as mentioned in the above posts, you only need to achieve necessary clearance for the chain (on both sides of the 11t cog), have a sufficiently-long 11t lockring (usually NOT a problem), and to be sure that the cassette width is ultimately sufficient for the lockring to actually compress the cassette forcefully upon installation (before bottoming out against the end of the freehub body).
The 1.1mm spacer might come in handy, but I believe the added width of the 11t cog will make it unnecessary.

The shift from 11t to the next-larger (13t or 14t) cog may have a bit of a jump to it as the cogs will not be HG-matched.

Last edited by dddd; 01-03-20 at 05:00 PM.
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Old 01-04-20, 08:47 PM
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Honored to be summoned by you, @verktyg!

7-speed is more my niche, but I do have a couple of new HG50 8-speed 13-26s lying around for future projects. They don't have any spacers between the cogs, or underneath the lockring (and none are shown in the documentation). The 13T is just under 5mm thick.

Do your 12T cogs have any letter codes on them? If I'm reading Sheldon's page correctly, a 12T marked "W" will actually index perfectly with the 13T of an 11-30! https://www.sheldonbrown.com/k8.shtml

If you don't have markings to go by, my inclination would be to try one of the ~5mm 12T cogs and a 12T-compatible lockring, with no spacers! Good luck.
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Last edited by ThermionicScott; 01-04-20 at 11:44 PM.
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Old 01-05-20, 10:20 AM
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verktyg could you explain your choosing of a 9 speed chain for this project?

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