I have an 11-23 and a 12-27 ultegra cassettes and I’m doing a race this weekend where I would like the 27 on the way up a long hill, and then the 11 on the way down. I was thinking I could just mix and match cogs to get an 11-27, but wasn’t sure if it would actually work. Doesn’t anyone have any experience with this?
-Brandon
Yes, you can mix and match cogs. However, I must question why anyone needs an 11 in a tri. If you are going fast enough to spin an 11 you should be in a full tuck or at least not pedaling. I’ve never quite understood why anyone but a pro cyclist needs and 11.
If you are comfortable taking apart cassettes this is not that tough.
Chad
crazy as it sounds, the new Shimano 7900 has an 11-28 cassette, and I have one, sorry.
The downhill from 3 stage hill at Triple T is a good place to have an 11.
jaretj
Perhaps if you had a compact crank…
OP didn’t specify his race was a Tri…
FWIW, I have an 11 on my TT rig; sure I don’t use it much (slight downgrade with a good tailwind, which does come together occasionally), but then on the vast majority of courses I don’t use the 21 or even the 19, either. They’re basically just ‘spacers’ to keep me running closer to the middle of the block for a slightly better chainline.
The Dura-Ace CS-7900 is available in 11-27.
It’s a road race and I have a compact crank on my road bike 
-Brandon
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I’ve found that if I’m in a tuck over 35mph descending in a tri, I’m just as fast as, or faster than, everyone I’m near who is in aero who is pedalling. I would guess that for bigger bike studs that number would be closer to 40, but, in any case, I’m not using my legs or CV system and they are.
I have not done this, but I think it will work. I’m assuming you mean 10 sp. IIRC, Shimano cassettes have the 3 largest cogs on one carrier, with the next 2 on one carrier, with the remaining 5 as single cogs. If that’s right, then
11x23 = 11, 12, 13, 14, 15, |16, 17|, |19, 21, 23|
12x27 = 12, 13, 14, 15, 16, |17, 19|, |21, 24, 27|
You’d use the five individual cogs from the 11x23 and the 2 carriers from the 12x27 yielding
11, 12, 13, 14, 15, |17, 19|, |21, 24, 27|
Seems like it would work to me.
I’ve been using SRAMs 11x28 for big hills. 11, 12, 13, 14, 15, 17, 19, 22, 25, 28 – vs Shimano, an extra tooth in the last 3 gears. However, I’ve been thinking about IRD’s 11x28. 11, 12, 13, 15, 17, 19, 21, 23, 25, 28. Give up the 14, get more 2 tooth jumps and 1 more gear from 17 on. That may help the more gravitationally challenged among us.
If you really need an 11, just take the 12 off your 12-27 cassette and replace it with the 11.
So you lose the 12; big deal. Unless the race ends in a sprint where you know you need the 12, it won’t matter.
I’ve been running my cyclocross (dirt road) bike with an 11-13-…-28 cassette for a while and it works just fine.
for 300 bucks…
you can go with Interloc race design…IRD…they make a 11-28 in 9 and 10 speed for 79 bones…I use the 9 speed with ultegra…just slapped it on the rim, works great…no adjustments needed.
Perhaps if you had a compact crank…
Yeah, great combo is a compact double (50/34) with an 11-28 cassette. Good top end (50-11 is a higher ratio than 53-12) and good low end of 34-28 for climbing. You miss out on some of the mid gear spacing, but I can deal with that.
I sell the Dura-Ace CS-7900 cassettes with my bikes for $160.
According to Shimano, if this is 10 Speed Dura-Ace we’re talking about, the DA 7900 11-27 and 11-28 are only compatible with the 7900 rear derailleur. Not even the 7800. The remaining DA 7900 cassettes (e.g. 11-25) should work with 7800 series.
That’s what they say, anyway. What it means in the real world is beyond my experience.
Ahh, well, please forgive me then. I always assume, this being a triathlon website that folks are asking for tri races.
Chad
You’d use the five individual cogs from the 11x23 and the 2 carriers from the 12x27 yielding
11, 12, 13, 14, 15, |17, 19|, |21, 24, 27|
I've been rocking this for hillier races. Works fine.