AMoney

I have the Shimano CS-HG800 11-34 11 Speed Cassette. I had my shop swap out the 11t sprocket for a 12t sprocket. I am looking to swap back to the 11t sprocket, and this time I would like to do it myself. Do I need to make any adjustments to the derailleur? If so, one which ones? My guess would be the H-Screw but I don't know for sure.

Bill Kapaun

You "shouldn't" have to touch any screw if you are using the same larger cogs.

Did they use your old 11T lock ring or a 12T?

FBinNY 

The RD is unaffected by this change. Think about your hunch re: the high gear limit. Why would you change that, since the 11t sprocket is in exactly the same place as the 12t it replaces?

As Bill hinted, 11t sprockets call for a special reduced OD lockring. If you're not sure just eyeball it, and confirm that the lockring OD is about 1/16" below the troughs of the sprocket, so the chain won't touch it.

SoSmellyAir

Not necessarily. For example, I have two Ultegra CS-R8000 cassettes, 11-28 and 12-25, and they both have identical lock rings. But Shimano 10-speed Ultegra CS-6700 cassettes have different lock rings depending on whether the first cog is an 11T or a 12T.

FBinNY 

You inferred too much from my statement that 11t sprockets need a smaller lockring. That's true because "standard" lockrings are too large and overlap the teeth.

HOWEVER, that doesn't imply that the smaller lockring won't work with the larger sprocket.

AMoney

That's correct. I swapped back to the 11t sprocket this morning. It is shifting very well. I didn't need to make any adjustments to the derailleur.

grumpus

Sounds like you're using the smaller lockring on both cassettes - that's fine, but the original larger 12t lockring will stop the chain fully engaging with the 11t sprocket.

SoSmellyAir

The same size lock ring comes with both 11-28 and 12-25 Ultegra CS-R8000 cassettes. It works just fine because the respective smallest cog in each cassette -- 11T in the former, 12T in the latter -- has the same sized opening. Shimano does not make a larger lock ring for the 12-25 cassette.

grumpus

It might not have been supplied with your cassette but there is a Shimano lockring that is too large for 11t top sprockets. It's the same thread size and uses the same tool but has larger outside diameter which interferes with the chain on 11t sprockets. This was the standard size before 11t top became common.

FBinNY 

This is beating a dead horse.

The fact that we reminded the OP to confirm that he had a lockring appropriate for 11t in no way implied that it wasn't so.

In fact, I even mentioned what to look for to be sure.

Yes, some 12t cassettes come with the same lockring as comparable 11t cassettes. But not all, and that's the point.

BTW not long ago we had a post by someone who went months unable to use his 11t sprocket. Turns out he had the wrong lockring, so apparently it pays to check.

KCT1986

For the Shimano road 11 speed cassettes, the standard lockring is the smaller 11T capable type. This works since the outermost sprocket is designed for this lockring. What is different is that the 11 speed cassettes uses a different 12T (or larger) sprocket depending on whether it is outermost or second outer position.

For 10 speed cassettes, the same sprocket (say a 12T) was used as the outermost sprocket or second position. Since this type of sprocket was used for both setups, it had an undercut area for the outermost sprocket to 'nest' into when in the 2nd position, and also had serrations for the lockring when used as outermost. The difference in the serrations was the reason that Shimano used specific lockrings.

SoSmellyAir

Yes.

As noted by KCT1986 and me above, this was the case for 10-speed Shimano cassettes. But this does not apply to the specific cassette mentioned by the OP, i.e., an 11-speed CS-HG800, which is part of the 11-speed Ultegra CS-R8000 cassette series. I suppose it is possible (albeit unlikely) that the LBS had installed a bigger lock ring when replacing the original 11T with a 12T cog. But assuming that the LBS was familiar with the most recent generation of 11-speed Shimano cassettes, it would have been more likely that it simply used the original lock ring that came with the cassette, which works for both 11T and 12T first cog.

KCT1986

Yes, If the shop replaced the 11T with a Shimano 12T sprocket designed for 11 speed, the sprocket would not have the recessed area and the serrations would be adjacent to the inner hole. The original lockring for the CS-HG800 would be fine.

If another type of 12T sprocket, with a recessed area that enabled it to be used as a second position, then a 12T type lockring may(?) be better.

urbanknight

I resemble that remark, although in my case it was a 10 speed cassette. Since (I believe) Shimano 10 speed lockrings could be put on 11 speed cassettes, it still indeed pays to check.

FBinNY 

I think, we're dealing with semantic, logical, and philosophical differences.

Statements referencing a smaller diameter required for 11t vs. 12t don't imply any specific interchangeability, nor that the smaller lockring wouldn't work with 12t. They simply mean that the maximum diameter for an 11t lockring is smaller than for 12t, no more and no less. Reading more into that, and "correcting" it, stems from a semantic and logical error.

But there's more at play. Some people are very up to date on brand specs, while others like myself prefer to deal with operating principles. So, rather than referencing spec sheets, I prefer to post info that folks can apply any time.

It's kinda like giving fish vs. teaching how to fish. I don't claim either approach is better or worse, they just reflect different worldviews.

Also consider that more people read threads than the OP, so I can't see why you'd object to a reminder to confirm lockring diameter when using 11t.

But, let's be real, neither of us is going to change, and that's just the way it is.

Bill Kapaun

Do you really think the OP cares what you have? Especially since they don't have either of YOUR cassettes.
They just wanted some info.
Anything after post #3 is a waste.

SoSmellyAir

It's all good. I answered the OP's inquiry specifically, while you and KCT1986 laid out the framework for answering the entire category of questions.

No, but see above and my post # 12.

Bill Kapaun

Anything after post #3 is still a waste.