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12-25 or 12-27?(30 posts)

12-25 or 12-27?hrv
Feb 13, 2002 8:55 AM
I went from a 105 triple to double a couple of weeks ago, and kept the 12-23 on the back. After recently doing a 5 mile climb while barely able to 'spin' in the 50's, a 25 or even 27 sounds pretty good. Most of the people I ride with are strong riders/cat 3 racers and use 25. Does it make sense to get a 12-25 since I already have a 12-23? Would there be a disadvantage of running a 12-27 as my only cassette? I will be doing time trials and starting to road race. Is having more than one cassette a fact of life?

And I swore up and down that I would never become a cog chaser!

Feb 13, 2002 9:06 AM
I'd skip the 12-25 and go with a 12-27. The only difference between the two are with the two largest (climbing) rings; the rest of the rings are identical.

The 12-25 goes from the 21 to a 23-25 while the 12-27 goes from the 21 to a 24-27. I find the 24 to be a nice compromise of the 23-25 rings of the 12-25, and the 27 ring is a real nice bonus to have for a lot of reasons which all have to do with getting to the top of the hill.

Keep your 12-23 for racing. It is like the 12-25 except that the 25 is dropped in favor of a very valuable 16 cog.

To change cassettes yourself, invest in a chain whip and a lock ring removal/install tool, which looks like a big nut.
It helps if you have a vise. Changing cassettes won't take much more than 5 minutes once you do it a time or two.
one important thingcyclopathic
Feb 13, 2002 9:28 AM
when you change cass don't forget to add extra links (2 for 25 and 4 for 27). Some forget, you'd be surprized.

On 12-25 vs 12-27 I'd go with Starliner I own 12-23, 12-25 and 12-27 and I don't use 12-25. It's either 12-23 or if I need bigger I go to 12-27, I don't feel much diff btw 23 and 24, yet 27 gives lower bail out gear good luck
Add links? Really? Please explain.nigel
Feb 13, 2002 3:52 PM

I understand the logic, but I haven't heard of this being done. Granted, I haven't asked around too much, but I haven't read this in the Zinn book or elsewhere. I use a 12-23 normally but switched to a 12-27 for "winter spinning," putting in base miles in the hills without working TOO hard and focusing on a high-rev spin. I didn't add links, and things were just fine (until a local wrench messed with my cable while installing a new headset--I've since fixed the problem with the aid of Feathers McGraw from the board here).

It sounds like it would make sense, but is it really necessary or recommended?

Big thanks,
would really depend oncyclopathic
Feb 13, 2002 5:47 PM
who and how installed chain.

Shimano recommended chain length is big/big+2, I usually put more (just make sure small/small still has enough chain tension). No it is not really ness, but if chain is too short and you overshift you'll screw your drivetrain.

The safest way is to install chain with biggest cass you have (12-27) then swapping cass wouldn't pose any threat
12-27 ditto.look271
Feb 13, 2002 10:19 AM
My favorite cog on the 12-27 is the 24. Low enough to get up MOST things, but if you're really toasted or on a really big hill, that 27 is a welcome addition.Hey, Lance spins uphills, why shouldn't you?
Feb 13, 2002 9:06 AM
get a 50 big ring
re: 25 or 6 to 4 (nm)bb
Feb 13, 2002 9:07 AM
Staring blindly into space,collinsc
Feb 13, 2002 9:17 AM
Getting up to splash my face,
wanting just to stay awake, wondering how much I can take.
Should I try to do some more? know how it goes
re: 12-25 or 12-27?Soup
Feb 13, 2002 9:10 AM
two options
1. swap to the 12-25

2. Start a lifting program, squating, dead lifts, stiff legged deadies, good mornings. Do this and continue riding to maintain endurance and you'll start ripping up those hills. If you do this make sure you're getting enough protien and calories. Eat around a 1 gram of protien per pound of body weight.

good luck
Feb 13, 2002 9:18 AM
To be quite honest, unless you have knee problems I would stick with the 12-23 and work on your strength. I don't know anyone who races with a 25, unless you are in a really, really, hilly corse, like the san fran grand prix. When you go to a 25 you give up a 16 which is really needed in crits and road races to dial in with the pace. Work on your strength, and you 23 will be perfect for 99.99% of riding.
Depends on where you live and race. (nm)allervite
Feb 13, 2002 11:01 AM
Nothing wrong with a 12-25. A lot of the pros at the SF GP used a 27, and they were still doing the "Paper Boy" up the hill.
my experience is nice to have bothPaul
Feb 13, 2002 9:18 AM
I have both the 12-25, and the 12-27. I prefer the 12-25 as I found when standing I was spinning too much in the 27. When I do extremely hilly centurys, I put the 12-27 on, otherwise I just use the 12-25. You will build up to it if you do enough hill training.
Feb 13, 2002 9:24 AM
I can only speak for myself, but I find the spacing on the 12-27 to be too big (21-24-27). I ran 12-27 for two years before I got sick of the jumps and switched to 12-25.

The reality for me is that there is nothing I've encountered yet that I really need a 27 for. And there are some nasty and brutal climbs here in the San Francisco Bay area. But I'm a natural born climber. Your results may vary.
Got Hills?grzy
Feb 13, 2002 9:51 AM
It all depends on the type of riding you do. Big long steep grades on century and longer endurance type rides favor the 12-27. The ratios work out to the following, multiply by 27 to get gear inches:


Your triple in the 32/23 gave you a 1.39:1 ratio while a double witha 27 would give you a 1.44:1 ratio. Notice the huge jump when you kept the 23 on the back but your front CR went from a 32 to a 39 - 1.39 to 1.7. That you're having problems with the 23 is testament that it's too stiff for you. Is a 25 going to be enough? Probably not based on your expereince.

However, you say you're going to be racing so tighter ratios are better and they'll snicker at your "dinner plate" cogset. Macho types will hang on to their 12-23 as being the only way to go, but they usually end up pretty cooked after long rides with lots of climbing. In fact you can usually pass them up well before the end. True bike gods do it all in a 12-23 and are all showered up before you even finish. It all comes down to what works for you and in the final analysis cog sets really aren't very expensive. Experiment and borrow cogsets if you can - just remember to lengthen your chain so that you don't bend the rear der. when you accidently shift into big/big and jam the drive train - this is an expensive lesson that not everyone needs to learn first hand. ;-)
Got Hills?LC
Feb 13, 2002 10:16 AM
A standard Shimano triple has a 30, not a 32 tooth chainring. This puts the 30x23 all the way down to 1.30, which is much lower than the 1.44 you get on the 39x27. Your old 30x21 was 1.43, so use that as a guide to consider what the biggest gear you need to gut up the hill. Your used to spinning up the hills in the triple, so keep on doing it like Lance and get the 12-27. You always have the option to shift to the 24 or 21 if you feel strong, and either way you loose the 16 cog.
a question...g-money
Feb 13, 2002 10:35 AM
I just went to a 12-27 from a 12-25. Is it really nec to add links? My chain/der looks fine even in big/big. From my experience it looks to be ok. Just wondering.

Also, what is the majic of the 16? Unfortunatly, I've always run Shim cassettes with no 16. What's the deal... Is it possible to replace the 15/17 combo with a 15/16 or something? is it really worth it? Just curious...
a question... 16mixinbeatz
Feb 13, 2002 10:47 AM
For riding in crits and road races, It is benifitial for me to have all the gears where I really need them. I would rather have more adjustment range in the middle gears than a 25 or 27 sitting on the end, that I would never use for this type of riding.
should be okay with 106 links for a 12-25 or a 12-27Paul
Feb 13, 2002 10:51 AM
On a road bike with double crank (53/39).

Good point about chain length, have to be careful.

In big CR, and smallest cog, pulleys should be 90 deg (perpendicular to the floor), when in smallest CR, and largest cog, derailleur should be about 45 deg to the floor. Should have at least an inch of play in this position (moving the derailleur up towards the chain stay). 106 links seem to be a common length.
zinn says...Js Haiku Shop
Feb 13, 2002 11:07 AM
...route the chain, skipping the derailleurs, around the big ring and big cog, and measure it to one full overlapped link at the end, then get rid of the excess.

this right?
grzy says....grzy
Feb 13, 2002 2:13 PM
Just run the chain through everything in the big/big combo and get rid of everything else. Same difference I suppose - except I don't have to re-route things.

It's a really common mistake for someone to install a cog set with a large enough difference that you can lock-up the drive train and tweak the rear der. Going from a 25 to a 27 may not be a problem, but if you start with a 23 it will be. I've done it. ;-(
re: 12-25 or 12-27?pmf1
Feb 13, 2002 10:50 AM
If you find yourself riding in varying conditions, multiple cassettes is going to be a necessity. I even swap out small chain rings (have 42, 39, 38). It doesn't take long and its nice to have the right gearing for the right situation. Assuming you ride Shimano, Ultegra cassettes are much cheaper than DA and last longer. If you have Campy, its a different story. Either way, there is nothing wrong with having several cassettes.
re: 12-25 or 12-27?jrm
Feb 13, 2002 11:14 AM
The wider the selection the wider the versatility, but the more the weight.
Cog chaserElefantino
Feb 13, 2002 12:13 PM
I have a 12-25 on one bike and a 12-27 on the other. There is a difference. The 25 is the flats bike, the 27 is the hills bike.

They're not that expensive. I picked up the 27 (Ultegra) on eBay for $18. And they're easy to swap out.

Chase away.

Cat 3s with a 25?McAndrus
Feb 13, 2002 12:14 PM
Where do you live? In the midlands of South Carolina it's pretty hilly but I've never seen a Cat 3 with a 25. Heck, I run a 12-21 myself. Of course that changes to a 13-26 when we go to the mountains.

As to a 16 gear, I strongly recommend it. In fact I used to ride a 12-23 and went to a 12-21 just to get an 18 as well. In a fast group those close gears can make all the difference.
re: 13-27(+16)Chen2
Feb 13, 2002 12:25 PM
I'm converting my 12-25 and 12-27 to 13-25 and 13-27 with 16's in the middle. They work great, and that 16 is a sweet gear and I need it more than the 12. If I had to choose between a 12-25 and a 12-27 I guess I'd take the 12-27, but "both" is the best answer. If you've got enough chain for the 27 you don't need to shorten it to switch to the 12-25. I've got wheels set up so I can switch in one minute or less.
re: 13-27(+16)MikeC
Feb 13, 2002 6:27 PM
I agree. I ride Campy, and went with the 13-29 (which includes a 16). I've found that I can always pick up my cadence enough to keep up when everyone else is in a 12, but when the 25 riders are dying, I'm still spinning away on my pie-plate!
re: 12-25 or 12-27?Len J
Feb 13, 2002 12:44 PM
I live & ride mostly on the flats (Eastern Shore of Maryland) so my cassette of choice is a 12X23. When I head to the Western Shore or go elsewhere where there are hills I use the 12X27. In my oponion, there is not enough difference between the 12X27 & the 12X25 to warrant having both. (as someone else pointed out the only difference is the last three cogs). I subscribe to that old rule of thumb that says to always try to have one more shift than you need. By using the 12X27 you probably can climb most hills in the 24 and you will still have a bailout to the 27.

Other options to extend your gearing with a double are:

-Some here have used a 28 or 29 cog with Shimano with some luck (Even though Shimano recommends not using over a 27).

-Change the 39 chainring to something smaller,

-Replace the rear road Der. with a mountain Der. (XT or XTR are both compatible with 9 speed Brake lever shifting). this will allow you to use a rear casette which includes up to a 34 tooth ring.

-Do hill intervals to gain climbing strength.

Some of this is a function of wether you spin or mash and where you ride. Look at a gearing chart & see what different combinations give you in terms of speed at certain cadences, comnpare those to a gear & cadence & speed you have experienced & see what you think would work.

Increasing strength is the cheapest solution, next cheapest is probably a cassette change.


Excuse my cultured idiocy but...Crankist
Feb 13, 2002 8:46 PM
...isn't that 105 triple rusting on the shelf in the back of your garage just the ticket?
To summarizehrv
Feb 14, 2002 8:25 AM
Thanks for the great posts. Turns out the LBS will let me try a 12-25 and 12-27 so I'll put them to the test.

The intent of my initial post wasn't to ask how to get the same gearing with my double as with my triple, as some of you have concluded. I was just asking to compare a 12-25 to a 12-27, like the topic said. I worked hard on not needing the 30 ring and hadn't used the it for almost 2 months. Going from a 42 to a 39 ring made all the difference in staying strong with the group and not working any harder. I do feel that riding the 42 was a great strengthening tool and sometimes force myself to drop down a gear in the back to simulate it.

Got hills? How about 'got flats?'. Living in the valley of Mt. Hood, Oregon allows for very little flats riding. Most people who ride/train here use at least a 25, and when they go to other places to race use other cassettes. I'll use my 23 when I enter my first race and the post about using a 12-21 makes sense too, esp. in a time trial.

Thanks again,
hrv, newly inducted member of the CCA (cog chasers anonymous)!