Sheldon Brown used to do something like this with 9sp to make 12-30. IRD makes a Shimano compatiple 11-28. Inexpensive, but heavy. Google Interloc Racing. Cycle Dynamics makes individual titanium cogs with pvc spacers. I have one of these with extra cogs so I can run it as an 11-21, 11-23, and 11-30. I have run the 11-30 on both D/A 10sp and SRAM Force. No prblem on the D/A at all. It's very tight on the Force, but it does work. Light, but not cheap!

hth

just do it!

any tips

You are correct, you lose the 16...i did the same thing and combined a 12-25 and 11-23 for 11-25, so it goes 11-12-13-14-15-17-19-21-23-25. shifting may be a bit stickey from 15-17-19, but it works well enough. be sure to use the lock ring from the 11 though, it matters, not sure why. let me know how it turns out.

On campy the lockring for the 11T is smaller than the one for the 12T. I had never noticed a different size on Shimano, but with Shimano i always just use the one that comes with the cassette. On campy you buy the lockring seperate from the cassette, not sure why.

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Disclaimer: This poster is a sales rep in the bicycle industry

If you can suck it up for a bit, you will be able to buy a shimano cassette in 11-26 and every other flavor you could want soonish...

Maybe hit those hills a little harder too ;)

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Ryan
Engineer. Duathlete. Roadie. Human.
CAPA Cycling

At least on Shimano the lock rings are two different sizes. An 11 lockring will work on any cassette. A 12 lockring on an 11 cassette is too big and will cause the chain to skip in the 11.

don't put a larger cog outside a smaller one.
don't put two of the same cogs on.
;P

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...
Run like you stole something
Formerly Fueled by ZYM

anyone done this with a 11-23 and a 12-27? details please..

It used to be even easier back when it was 8 loose cogs, now some of your intermediate and upper combos are fixed in pairs or threes. For an 11-23 x 12-27, though, I *think* (don't have any in front of me, so working off memory) you can just go 11-12-13-15-17-19/21-23/25/27; ditch both 14s, the duplicate 12, 13, & 15, the 16/17 pair, and the 19/21/23 set.

Why don't you just buy a Dura-Ace 11-25, 11-27, or 11-28?

Product: Shimano HG80 9sp 11-28t Cassette
ID#: BPC351298

THis is for mountain bike use. Think it would work with ultegra 9 speed. not much heavier than the 12-27. And it is HG.

interesting I may have to give this a go

let me know how it goes!

done it? certainly. got a 27 cog and took out one of the others ( i forget which) and have never noticed any hitch, drawback or whatever. i did it thinking everyone did such, so i guess i sallied forth in blissful ignorance...and it happened to have worked out well.
peggy