# Quick Question: 12-25 or 12-27?



## rickreyn (Jul 27, 2004)

It's time again to change out my cassette and chain. I use Ultegra cassettes. Last time I changed out a 12-27 for a 12-25. I liked the gearing on flats and rolling hills but I could not get an easy enough gear to ride up my annual 3,000 foot Blue Ridge mountain, which I did twice before the 12-25 change. My question is in two parts: a) the 12-27 is indeed what I need to get the gearing for the tall mountains (granny gear), and 2) will I be able to find the gears I am now comfortable using (big ring, mid way) somewhere on the 12-27? I'd like to avoid having to buy two cassettes. I have a triple 9-speed with Ultegra components. 2004 Specialized. Thanks.


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## Dinosaur (Jan 29, 2004)

If you only need the 27 for one annual ride, I stick with the 12-25. The only diff is the last three cogs: 21 23 25 or 21 24 27. I had a 12-27 on my old Ultegra bike and I liked the 24. If you ride a lot of steep hills a 27 is nice. Your other option (which sounds like you don't want to do) is have a spare 12-27 set aside. That's what I'd do.


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## EMB145 Driver (Aug 17, 2006)

Like Dinosaur said, they are the same cassette except for the 27 vs 25 and 24 vs 23 on the lower geared portion of the cassette. I'd get the 12-27. You get basically the same cassette with one lower gear, which might help when it gets steep.


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## pmf (Feb 23, 2004)

I'd get the 12-25 and save your old 12-27. It'll still work for that one ride a year you do when you need it.

I can't see how you run out of gear with a triple and a 25 tooth cog. Must be some really steep stuff. 

Personally, I think a lot of people on this forum replace their chains and casettes too frequently. You don't have to get a new cassette everytime you get a new chain. And chains last a long time. At least for me they do.


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## maximum15 (Feb 6, 2004)

Another possiblity: If you rarely use the 12 tooth, you might be able to find a junior cassette in 13 - 27. I don't know if that combo was made, but you may want to look into it for a comparison.


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## av8torjim (May 11, 2009)

The difference is barely 2 gear inches. Not even a "full" gear with the triple. How steep is the annual ride? I have a 12-25 with a triple (53-39-30) and handle 20+ percent grades with it. I don't enjoy them, but can handle with with a 25. If the rest of your riding is not too hilly, I'd stick with the 25 and use the old cassette for the one ride per year as suggested above.


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## brucew (Jun 3, 2006)

I ride a 12-23 most of the time, replacing it with a 12-27 for the occasional hilly ride.

Reminds me I need to put the 12-27 on before the club ride Sunday morning.


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## twinkles (Apr 23, 2007)

Sram makes a 12-26 9 speed. Same as your 12-25 but with a 3 tooth jump between the 23 + 26.


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## bending guide (Jun 21, 2010)

running triple + 12-25 should get you to the top. Get the 12-25 and focus on developing your climbing skills. A gain in skills is way better than a gain in cog size.


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## Blue CheeseHead (Jul 14, 2008)

Dinosaur said:


> If you only need the 27 for one annual ride, I stick with the 12-25. The only diff is the last three cogs: 21 23 25 or 21 24 27. I had a 12-27 on my old Ultegra bike and I liked the 24. If you ride a lot of steep hills a 27 is nice. Your other option (which sounds like you don't want to do) is have a spare 12-27 set aside. That's what I'd do.


See I would advise just the opposite for the same reason. Actually the only difference are the last two cogs 23 25 and 24 27. Here is my logic, how much do you really use the 23 and 25? How critical are those specifc gears? A 24 is only about 4% off of either the 23 or 25.

I have three cassettes (10 speed), 12-23, 12-25 and 12-27. I like the 12-23 for everyday riding as it trades the 25 for an 18 (the 9 speed adds a 16 which is even more important). The 12-27 is required for an annual California trip with painful climbs and some of the hilly events around me. The 12-25 is the redheaded step child. I NEVER say, "Oh, I want the 12-25 today". It is only on a spare wheel.

In my opinion the 12-25 has no flat advantage over the 12-27 since 12-21 are all the same and does not offer the hill climbing advantage of the 12-27. The gear spacing from 21-23 vs 21-24 is not that huge of a difference and is not at as critical of a point on the cassette for maintaining the most comfortable cadence. Just my .02


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## rtarh2o (Dec 18, 2009)

I can't remember how my old 9 speed Shimano's were made but it seems like the largest 2 gears were together? That being the case buy a 12-25 and keep the 24-27 from your old cassette, swap out the 24-27 for the 23-25 when you need it a couple times a year. 
I also love the idea of the 13-27 if they were ever made, my favorite 9 speed cassette was a 13-23. We don't have many climbs around here but we do have a lot of wind so extra gears in the mid range is nice. 
Just some thoughts
Rusty


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## Elfstone (Jun 27, 2006)

Blue CheeseHead said:


> See I would advise just the opposite for the same reason. Actually the only difference are the last two cogs 23 25 and 24 27. Here is my logic, how much do you really use the 23 and 25? How critical are those specifc gears? A 24 is only about 4% off of either the 23 or 25.
> 
> I have three cassettes (10 speed), 12-23, 12-25 and 12-27. I like the 12-23 for everyday riding as it trades the 25 for an 18 (the 9 speed adds a 16 which is even more important). The 12-27 is required for an annual California trip with painful climbs and some of the hilly events around me. The 12-25 is the redheaded step child. I NEVER say, "Oh, I want the 12-25 today". It is only on a spare wheel.
> 
> In my opinion the 12-25 has no flat advantage over the 12-27 since 12-21 are all the same and does not offer the hill climbing advantage of the 12-27. The gear spacing from 21-23 vs 21-24 is not that huge of a difference and is not at as critical of a point on the cassette for maintaining the most comfortable cadence. Just my .02


At the moment I'm inclined to agree with this line of reasoning. I'm riding 50/34 with a 12-25 cassette and I find myself wishing for a lower gearing on some of the long climes out here in my neck of the woods.

Blue put it well when he said "Here is my logic, how much do you really use the 23 and 25?" and when I think about it, not much. Unless I'm climbing which there's a lot of out here in California. 

On my next bike I'm opting for a 12-27 and if I get around some flat areas rides, I'll purchase a 12-25 for flat riding. But the rides around here are mostly rolling hills and short steep climbs and long sustained climbs. But with the OP running a triple, the 12-25 may suffice.

Peace


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## Erion929 (Jun 10, 2010)

Blue CheeseHead said:


> See I would advise just the opposite for the same reason. Actually the only difference are the last two cogs 23 25 and 24 27. Here is my logic, how much do you really use the 23 and 25? How critical are those specifc gears? A 24 is only about 4% off of either the 23 or 25.
> 
> I have three cassettes (10 speed), 12-23, 12-25 and 12-27. I like the 12-23 for everyday riding as it trades the 25 for an 18 (the 9 speed adds a 16 which is even more important). The 12-27 is required for an annual California trip with painful climbs and some of the hilly events around me. The 12-25 is the redheaded step child. I NEVER say, "Oh, I want the 12-25 today". It is only on a spare wheel.
> 
> In my opinion the 12-25 has no flat advantage over the 12-27 since 12-21 are all the same and does not offer the hill climbing advantage of the 12-27. The gear spacing from 21-23 vs 21-24 is not that huge of a difference and is not at as critical of a point on the cassette for maintaining the most comfortable cadence. Just my .02




I am also thinking of going 12-27 to do the bigger hills in my area of Orange County, CA. For now, since I only started back riding 6 weeks ago, I will continue to train to try to get stronger on the 12-25. But since I have to stop 2-4 times on the biggest hills of the area, I don't really see how I can improve THAT much. Mayyyybe....but that's a LOT of improvement to be able to get up those hills without stopping.

For future reference, can someone tell me which cassette fits? I have an '09 Cannondale Synapse Carbon 3, with Ultegra SL and a DuraAce rear derailleur, specs say "KMC x10 cogs". I looked up the latest cassette, which is the Ultegra CS-6700 but it doesn't have the 12-27. They only have 11-23, 11-25, 11-28, 12-23, 12-25. But I saw the previous generation CS-6600 that had a 12-27.....is that the one that would fit my bike?

**


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## Blue CheeseHead (Jul 14, 2008)

rickreyn said:


> It's time again to change out my cassette and chain.


I forgot to ask, why are you buying a new cassette? Chains will last me about a season (3,500-4,000 miles) but cassettes will last much longer, especially if you replace your chains regularly. They do not wear together to the point where a new chain would be damaged by using an old cassette.


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## bas (Jul 30, 2004)

rickreyn said:


> It's time again to change out my cassette and chain. I use Ultegra cassettes. Last time I changed out a 12-27 for a 12-25. I liked the gearing on flats and rolling hills but I could not get an easy enough gear to ride up my annual 3,000 foot Blue Ridge mountain, which I did twice before the 12-25 change. My question is in two parts: a) the 12-27 is indeed what I need to get the gearing for the tall mountains (granny gear), and 2) will I be able to find the gears I am now comfortable using (big ring, mid way) somewhere on the 12-27? I'd like to avoid having to buy two cassettes. I have a triple 9-speed with Ultegra components. 2004 Specialized. Thanks.


is that a 42 tooth or 39 tooth middle ring?

just wondering, 2004 was about the crossover year.

i have the bastard 42 tooth. 42x27 has to be very close to 39x25. check a gearing chart.


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## Reynolds531 (Nov 8, 2002)

if you have a 30 tooth granny chain ring in front you could change it to a 28 and keep the 12-25.


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## Cableguy (Jun 6, 2010)

I recently switched to a 11-28 (10 speed), I had previously been riding with a 11-25 (10 speed) for over half a year. After using the 11-28 for a month, and all I can say is I'm dumbfounded why more bikes don't have them.

Absolutely *love* it, I don't feel like my riding has been impacted in any other way than positively. I'm able to climb more effectively with bigger granny gears in each chain ring. In the big chain ring instead of spinning up hills at 80 cadence, it's now 90. When it starts getting steep, I find the ability to just keep my cadence up more important than shifting in smaller increments those last two gears. The only difference between the 11-25 and 11-28 is the former goes from 21->23->25 and the latter goes from 21->24->28. In other words, those last two gears. 

Here's an example that should sum up my experience pretty well. Starting in 50-21, let's say I'm pushing hard at 90 cadence. It starts to get steep and my cadence drops by 10 down to 80, so with the 11-25 cassette I switch to 50-23 and without pedaling harder my cadence goes up to 87.6. I'm already pushing it hard, so I can't really afford to pedal harder without going into the red. Alright, this cadence is good I'll stick with it. Now it gets even steeper and my cadence drops another 10 down to 77.6. I don't prefer this, so I switch to 50-25 and now my cadence goes up to 84.3. I can deal with this, my ideal cadence is 90ish so I suppose I'll just power grind a little at 84.3. No biggie, I'm out of gears in the big chain ring anyways. Now it gets even steeper and my cadence drops by 10 again, down to 74.3. I'm not a big fan of this cadence, it's workable but definitely not ideal. I can either A) bear with it, or B) switch to the small chain ring up front and lose a chunk of my momentum as I deal with the awkward change (and if it's about to flatten out soon, this may not be an option as I'd just need to switch back yet again).

Now let's use roughly the same experience above, but with a 11-28. Starting in 50-21 I'm pushing just at what I can sustain running 90 cadence. It gets steeper, cadence drops by 10 down to 80. I switch to 50-24, cadence goes up to 91.4. Great. It gets harder and now my cadence drops by 10 again down to 81.4. I switch to 50-28, and it shoots up to 95. Good. Now the hill gets even steeper, and my cadence goes down by 10 to 85. I'll stick with this no problem - it's certainly better than 74.3, or having to mess with the small chain ring.

What do I *lose* with the 11-28? On paper, it's very tempting to say "You don't get as smooth of a shift with those last two gears." In experience, I say "Actually, I lose nothing that I need..." What do you use those last two gears for in the cassette? Climbing, and that's when your cadence tends to fluctuate the most. Makes perfect sense to me to have bigger gaps in those gears to deal with the biggest fluctuations.


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## Matt1986 (Mar 19, 2010)

Would you really run 50-25 on a 12-25, or 50-28 on a 12-28? That strikes me as entailing some pretty serious cross-chaining..


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