The 12-25 has an "A" code 16T cog, while the 11-32 has a "B" code 16T cog. The difference is the shift ramp machining. While you're Frankencassette will probably work OK, you might experience some less than smooth shifting either way at the crossover point.

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"They're made of latex, not nitroglycerin"

I have done it and what gary p says is correct.

There's a lot of that type of thing in mixing and matching cranks, chains, and cassettes, as well as mixing 10 and 11 sp parts, and sometimes while mixing SRAM and shimano. It will probably work, but all matched parts have those shift ramps machined for best shifting.

As far as I can tell, Shimano doesn't make a 16T 11-speed cog with shift ramp machining for a one-tooth step on the high side and a two tooth step on the low side. It's either 1 tooth step both ways (A-code) or 2 tooth step each way (B-code).

Not sure exactly what you're trying to accomplish, but maybe you could get there with the new Ultegra 11-30 cassette and going down in size on the front chainrings. No 16T on that, but the 5 smallest cogs (11-15) are in single tooth steps. With 2T smaller front rings, the drive ratio with the 15T is awfully close to what the it is with the bigger chainrings and the 16T. Same with the 30/32T biggest cogs.

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"They're made of latex, not nitroglycerin"

 

Thanks for the detailed response!

I have a 52/36 with Q rings. I'm currently using a 11-28 SRAM cassette that has a 1 tooth jump from 11 to 17 - I really love it! Maybe a 52/34 would still work hopefully without any shifting issues and that would allow me to keep my 52 q ring. I don't care too much about the inner q, I could swap it for a 34 round if it would work.

The 11-30 sounds like a good compromise. Most of the time when I'm not climbing or descending I'll be averaging around 24.5mph so actually the 15 cog would be more important than a 16. But in case of a head wind a 16 would have been nice. I really only need a 30 or 32 for 4 climbs where a 52/28 would mean grinding it or make me go above threshold for a couple of minutes.

I get it. I bought a 2x9-speed road bike about 3 years ago. Quickly realized I wasn't using the top couple gears of the 12-26 SRAM cassette at all here in the flatlands, but there were a lot of times I wanted for something in between the 15 and 17 or the 17 and 19. I swapped in a 14-25 "junior racer" cassette with single-tooth steps between the 6 smallest cogs. Turned me into a cadence whore, straight away. FWIW, I still ride that cassette on that bike. I have enough power now to, on occasion, spin out briefly on some of the longer, steeper hills around here ("longer" and "steeper" being relative terms). It's a price I'm willing to pay to have 16T and 18T cogs which I still use a lot.

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"They're made of latex, not nitroglycerin"

Any reason why you wouldn't go with a 50/34 in the Q rings and a 11-28 or 11-30 cassette?

If the 52-11 is bigger than you use perhaps a 50-11 is more reasonable.

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Suffer Well.