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Should I go 12-23 or 12-25?(22 posts)

Should I go 12-23 or 12-25?Larry Klassen
Aug 6, 2003 8:56 AM
I ride in a fairly flat area, but strong winds. Nevertheless, I do get to traveling sometimes, and would like to be able to climb as well. Currently I am running an 11-21, and find it to big to push these gears. Will 12-23 make a big enough difference, or should I go with 12-25?
re: Should I go 12-23 or 12-25?JimP
Aug 6, 2003 9:05 AM

I am assumming that you are riding with a 9 speed cluster. The question you must answer is whether you really want/need the 16 cog. The 12-23 has the 16 where the 12-25 skips it. If you don't use the 16, then go for the 12-25.

I am running 9 spd, is 23 a big enough jump though?Larry Klassen
Aug 6, 2003 10:21 AM
I'm not really sure if I use 16 alot or not, I just shift (I know, I don't pay enough attention). I do find that 21 is too big a gear for me in the big ring on moderate climbs (ie. fairly gentle) as well as winds - I'd rather not have to shift into the little ring until I am doing a sig. climb - would a jump to 23 be enough difference (ie. is it a significant difference), or do I need to go to a 25 to really notice a change? Thanks again for your input.
How are you using your gearsasgelle
Aug 6, 2003 1:29 PM
> I do find that 21 is too big a gear for me in the big ring on moderate climbs

First of all you should avoid the big-big combination.

> I'd rather not have to shift into the little ring until I am doing a sig. climb

Why not. If you're running a 53X21 at 80 rpm, you're moving at about 16 mph. That corresponds to a 39X15/16. Why not shift to the small ring and save your drivetrain and get the benefit of smaller steps between gears.

To answer the original question, at 60 rpm pedal cadence, a 39X23 will move you 8.0 mph. The 39X25 gives 7.3 mph (9% difference). How fast do you think you'll climb.

has a gear calculator that lets you do these calculations for yourself.
Aug 6, 2003 11:18 AM
21 to 23 is hardly much difference on a steep hill. You might miss the 16 at first, but you will get used to it quickly.

Do some single speed riding. After that whatever 16 or 18 gears you got will seem like more than enough as long as the lowest gear is low enough to get you over any hill you might encounter.
Aug 6, 2003 12:06 PM
With a 13-25 you get the climbing help you need AND the 16 in the middle.
Does that come in UItegra?Larry Klassen
Aug 6, 2003 12:31 PM
Can you get 13-25 in ultegra? I'm pretty sure you can't in DA, right? I'm leaning toward the 25, if I can get 13-25 I will.
Yes, UltegraChen2
Aug 6, 2003 1:51 PM
The Shimano European web site has cassette charts and exploded views of all of their current 9-speed cassettes. If you go there look under Catalog, Road, Ultegra, Cassettes.
Yah, ditch the 12off roadie
Aug 7, 2003 8:30 AM
If you live in a fairly flat place, the chances you need the 12 are minimal, while a nice range of "corbcob" gears in the middle will feal wonderful. A 25 tooth "bailout" is certainly NOT unreasonable for occasional hills or really windy days.

Can you really pull 53/12 for any useful preiod of time on level ground? Bully if you can, but such gearing is really intended for descents (or maybe when you have a STRONG tailwind), not mashing along on flat ground.

Another option would be to keep the smaller gogset and replace the cranks with a set that allows something like 34/50 chainrings. Smaller front rings result not only in easier climbs, but also in smaller ratio changes per shift, so they can be great for flatland riding.
my philosophy: always go for the bigger geartarwheel
Aug 7, 2003 7:53 AM
I live in a hilly area, but occasionally ride in flatter areas with wind. Personally, I would miss having a 25 (or, in my case 27) more than I would a 16. I started riding when bikes only have 5-speed cassettes, so I am used to having larger jumps between gears. I could care less about having a tight "corncob" cassette when I'm facing a hill or steady wind. And there is a big difference between a 23 and a 25, if you need those gears. If you're a racer, stick with the 21 or 23.
my philosophy: always go for the bigger gearChen2
Aug 7, 2003 8:16 AM
Agreed, but you can have your cake and eat it too. I converted a 12-27 to a 13-27 with a 16 in the middle. For my wife I put together a 14-28 with a 16 in the middle, Shimano 9-speed. She runs in with her Ultegra triple.
did you just separate the cogs?rufus
Aug 8, 2003 6:15 AM
from the little spindles that lock them together and throw a 16 in the middle? at my strength, i'd rather have a 13-27 with a 16 tooth rather than a 12 cog.
did you just separate the cogs?Chen2
Aug 8, 2003 8:56 AM
No, I've never drilled out the rivets, if that's what you are asking. With Ultegra or D-A the 12 through the 15 the cogs are singles, not joined. With a 12-27 you can remove the 12 and 13, replace them with a 13 with built-in spacer, and add the 16 in the middle. I've done the same with the 12-25 to convert to a 13-25. But you can buy an Ultegra 13-25, on it the 16 is joined to the 17. For cog set charts and cassette exploded views go to the Shimano European web site. I bought my extra parts from His cogs are not necessarily Shimano, but they work just fine. I cannot detect any deterioration in shifting quality. Shimano won't sell individual cogs.
rivets, that's the word i was looking for.rufus
Aug 8, 2003 9:33 AM
i guess it's pretty easy to separate a cassette once you grind down the rivet heads holding them together. i guess you can just buy a couple of different cassettes, and mix and match, if you wanted to keep it all shimano.
re: Should I go 12-23 or 12-25?Banky
Aug 7, 2003 9:14 AM
Larry, I also live in a flat area, Fla, I changed from a 11-21 to a 12-25. The only difference I noticed was that I had the 25 and 23 for any hilly rides I did in northern Fla, I really did not feel any changes in my mid to low end gears in the flats. Plus the 23 rear gave me some bailout on the really windy days as well.
re: Should I go 12-23 or 12-25?maximum15
Aug 7, 2003 6:20 PM
I too am in a flat area, sometimes with strong winds. I do a lot of riding by myself and having a 16 in the back with the 39 up front is an excellent combination. At 80rpm, you will be doing better than 15mph, at 95rpm, somewhere around 17mph (don't remember the exact numbers). I am using a 12-23 on all my bikes now and it is working great. If you are a stronger rider, then consider the 12-25.
Aug 7, 2003 6:45 PM
"I am using a 12-23 on all my bikes now and it is working great. If you are a stronger rider, then consider the 12-25."
Is that what you really meant to say? You need to be stronger for a 12-25 than a 12-23??
Huh? Good Questionmaximum15
Aug 8, 2003 8:59 AM
That didn't make much sense did it? I meant to say, if you don't think you need the 16, then go with the 12-25. At my level, the 16 is a must have gear. A 12-25 doesn't offer a very good gear match up to the 39-16 without a fair amount of cross chaining (53-21).
Get them bothpmf1
Aug 8, 2003 8:52 AM
Cassettes aren't that expensive -- especially Ultegra cassettes. I've got every size and more than one in most sizes (extra wheels, wife rides too ...). Its easy to swap cassettes to match your riding conditions.

Frankly, the older I get, the less I use the 11-21.
Thanks folks...also, how do you customize cassettes?Larry Klassen
Aug 9, 2003 6:50 AM
I decided to go with the 12-25. I think I will miss the 39-16 combo, but I'll have to see. I too have been riding since there were 5 gears in back, but am getting used to tight clusters so that I can really fine tune my gearing. Nevertheless, we'll see. My only options were 12-23 or 12-25, so I went with the bigger. I'm doing a century in Sept. in Minnesota which is purportedly somewhat hilly, so I figured may as well be safe and have a bailout gear in case I bonk.

How difficult is it to customize your own cassettes, though? That may be a consideration for me at some point.

Again, thanks alot everyone, this is a wonderful source of sharing experience - I've had alot of questions answered here (and even helped out a little myself). Great community!
depends on the cassette(s)off roadie
Aug 9, 2003 7:30 AM
You generally need a source for the new cogs you want to add (old cassettes, shops with good stock) and the cassette you are customizing has to ahev a "break point" where you want to add the new cog. Some cassetes are just stacks of cogs and apscers held toghtehr with bolts- very easy to customize or canablaize. Some are made with "spiders" holdign the larger cogs, whcih are riveted to the spider. No way at all to add a cog into that spider, but its OK to add them on either side.

Sheldon Brown has an article about the construction details of various Shimano cassettes and how to make custtom cassettes.
In general, you can'tpmf1
Aug 11, 2003 5:28 AM
Modern cassettes are designed to work with the comnbination of gears they come in. You really shouldn't substitute gears from another cassette of different sizes. Shifting would probably not be as good. You could do this with older style freewheels, but you really can't with modern cassettes.

With all the sizes available, there really isn't a need to do this anyway. If you have Shimano, then the Ultegra cassettes are relatively inexpensive and wear a long time -- no reason not to have several in different sizes. Same with 39 and 42 small chainrings -- have one of each. If you have Campy, then its more expensive.