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I was looking at purchasing some Sram Rival components. Looking at the available cassettes, there is a big variety of sizes available:

  • 11-23: 11-12-13-14-15-16-17-19-21-23
  • 11-25: 11-12-13-14-15-17-19-21-23-25
  • 11-26: 11-12-13-14-15-17-19-21-23-26
  • 11-28: 11-12-13-14-15-17-19-22-25-28
  • 11-32: 11-12-13-15-17-19-22-25-28-32
  • 12-25: 12-13-14-15-16-17-19-21-23-25
  • 12-26: 12-13-14-15-16-17-19-21-23-26
  • 12-27: 12-13-14-15-16-17-19-21-24-27
  • 12-28: 12-13-14-15-16-17-19-22-25-28
  • 12-32: 12-13-14-15-17-19-22-25-28-32

Now I can understand why someone would choose a cassette based off of how many teeth the big gear has. Some people live in hilly or mountainous areas and desire a higher number of teeth. Some people live in flat areas where they simply won't use those cassettes with a lot of teeth on the big gear.

But why would anyone ever choose to buy a cassette with 12 teeth on the small gear instead of 11? 11 teeth = higher maximum speed. I doubt many people buying a nice set of components (Shimano, SRAM etc) would ever say "I don't need to go faster so 12 teeth is fine with me."

What's the point of 12 teeth when you could opt for 11 instead?

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The 12-25 gives you one more cog in the middle of the range, where you'll spend the most time and hence most want to "optimize". –  Daniel R Hicks Sep 26 '12 at 23:53
    
@DanielRHicks - exactly right. I have an 11-25, and I find I very often have a "gap" where a 16 fits perfectly. I can find the number of times I've used the 11 on one hand with a couple fingers and thumb left over. –  JohnP Sep 28 '12 at 18:17
    
With this many cogs in the back, do you still have a front derailleur? –  Kaz Oct 9 '12 at 17:33
    
yo voy en un11/21 y adelante 50/34 y voy demaciado rapido y en las subidas muy comoda –  user7823 Aug 17 '13 at 7:48
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@nuttyaboutnatty sram.com/sram/road/products/sram-pg-1070-cassette –  Jakobud Aug 30 '13 at 20:33
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11 Answers

up vote 19 down vote accepted

If you want to maximize your max. speed, go for an 11 tooth cog. If you want to maximize your average speed, unless you're a pro you probably are better off without it. Even cruising at 40km/h does not require and 11 tooth cog.

For example, take a look at this table, showing cruising speeds for a 11- 21 tooth cassette: cruising speeds for a 11- 21 tooth cassette

And compare to this table for a 12 - 25 tooth cassette:

cruising speeds for a 11- 25 tooth cassette

You can see that the 11 tooth cog is only really useful for cruising speeds that riders at the professional level can maintain, or for short bursts. So, like I said, if you aren't trying to break your own max speed record, you may be better off with a 12 tooth cog.

(Tables screen captured from bikecalc.com. Check it out.)

I remember reading a while back about how most riders can't maintain a high enough wattage output to make an 11 tooth cog worthwhile, but I couldn't turn it up. Maybe another contributor will post it.

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Just to clarify: in the context of these tables, "cruising" means pedaling at 90rpm. –  amcnabb Sep 27 '12 at 2:21
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"You can see that the 11 tooth cog is only really useful for cruising speeds that riders at the professional level can maintain, or for short bursts." This of course assumes flat terrain. People who live in mildly hilly areas might find themselves frequently cruising at a higher speed. It all depends on where you live and how you ride. –  amcnabb Sep 27 '12 at 2:26
    
Is the row along the top the number of teeth in the front chain ring? –  Jakobud Sep 27 '12 at 3:07
    
Yes, although practically you are very likely to be in a chainring with either 50 (compact crank) or 53 (standard) teeth while using a 12- or 11-tooth cog. –  Stephen Touset Sep 27 '12 at 4:10
    
It's all relative to the wheel size, crank length and front chain ring! I put an 11-28 freewheel on my compact MTB. It has 24" wheels and a 48 tooth front ring. The 13-28 wasn't doing it for me any more (got to the point that I'm climbing some hills using the highest 48/13 combo), but 11-28 is about perfect. The 11 gives that nice impedance when I stand up to pedal, and less spinning on declines. If I build more muscle, I will have to go for a 50+ ring. –  Kaz Sep 26 '13 at 0:44
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Some people will never get the chance to use the 11 teeth setting, whether this is through not being fit enough or another reason.

So they can opt for the slightly longer expected lifespan of the 12 (lower wear per tooth) and the slightly narrower gap between ratios which can make gear changing less of a struggle.

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You can compensate for the lack of the 11 tooth cog with a bigger chainring on the front as well. –  Kibbee Sep 27 '12 at 0:14
    
Your logic is that 12 teeth wears slower than 11 teeth just because there are more teeth to handle the forces from the chain at any given time? –  Jakobud Sep 27 '12 at 3:09
    
I only switch into my smallest cog when I'm taking off the wheel. –  user973810 Aug 30 '13 at 0:36
    
@Kibbee But the bigger chainring scales up all of the cogs! Your 25 is now faster, too. A chainring swap cannot do exactly that what a switch from 12-25 to 11-25 does. –  Kaz Sep 26 '13 at 0:47
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For me, and for many riders that come through my shop, the 11-25 is missing the critical 16t cog, which (at least for me) is the sweet spot. That is, the gear which I don't tend to spin out of, and that doesn't turn in to a grind fest.

If I'm doing a Euro trip, then I will run an 11-28, with a compact front. But at home, for daily riding, a standard 53/39 with a 12/25 is perfect.

For what it's worth, the 11t cog was designed to give a compact crank, with its smaller front range, the same or similar top speed as a "standard" setup, which at the time was a 53/12 maximum.

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In addition to the other answers, there's also cyclocross. People don't typically ride as fast in cyclocross as they do on the open road, thus lower gears might be better.

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The simple answer is that people (racers especially) like closely spaced gears so they pedal as closely as possible to their optimum cadence.

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And of course they know their optimum cadence down to three significant figures. –  Kaz Oct 9 '12 at 17:05
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Different strokes for different folks is all. Guys with arms like legs and legs like people have no need for a stump puller or even a 25 sometimes and are wishing for a 10 until they discover what a Campy set up costs while in my world of recreation and fitness a 12-28 seems almost perfect most of the time and I've even considered a 13 or even 14-27 from the 6600 junior cassettes. My first road bike was a '73 Fuji S10S 10 speed with a 14-17-20-24-28 and it seemed to be all I really needed (at the time) but now, at almost 70 yrs, bigger gears are my friend.

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This might not be welcomed but Michele Ferrari has a website http://53x12.com. The idea is to use smaller gear and higher cadence because using 11 cog requires tremendous amount of torque that makes it hard to pedal efficiently.

With 11 speed cassette now available, tighter spacing between cogs is achievable with 11 cog. But use 12 if you want to be efficient.

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One thing to ask yourself is "What is the max speed where I'm willing to expend energy, on a continuous basis, to maintain that speed?"

Yes, it's (maybe) nifty to do 60 mph down a hill, but the energy required to maintain that speed on any sort of continuous basis is astronomical. Most people have a max sustainable speed (on the flat) somewhere between 15 and 25 mph (depending on the individual), and it makes no sense to have gears that permit you to pedal (at a semi-normal cadence) at a speed faster than your max sustainable speed. It's more valuable to have the "in-between" gears than high-speed gears you will never really use. At most you might want to "push" the high end ever so slightly to take advantage of that rare day when you have a nice tailwind.

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It's nifty to go 60 mph down a hill if its in front of a comparable climb, and you want as much momentum as possible to carry you up. –  Michael Nov 14 '13 at 16:05
    
@Michael - Any momentum you "stored up" on that downhill will be lost to wind resistance in the first 30 seconds of the climb. In terms of "conservation of energy" it's a very bad deal. –  Daniel R Hicks Nov 14 '13 at 16:29
    
Right, it really depends on the hill. For my commute, in one direction a certain hill is a 60 second climb on my best day, but going the other way with enough momentum I can clear the next lower hill and still be going 20-25mph at the top. –  Michael Nov 14 '13 at 17:23
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Another way to see it is that while crosschaining is not that big of an issue with nowadays components (this has been confirmed to my on this very forum), the extreme cross-chainings are not very pleasant (noise, not completely smooth pedaling and so on,...). On the other hand, the second-to-last cog is very usable most on most (double) transmissions.

Therefore, with a 11-25 cassette, you can ride on "small-ring"/12 rather than "small-ring"/13 like you can on a 12-25 cassette (regardless of whether the "small ring" is 34, 39 or anything else).

In the same time, the 11 cog is not useless either as it can be used in downhills or sprints.

On the other hand, if you are sure with your extreme gears usage, having the tightest possible cassette is better: I could rephrase your question and say: "why would one buy a 12-25 cassette when you can have a 12-21 which will allow faster speeds and has smaller gaps (actually almost none)?"

The answer to that is actually the only right answer to your initial question and that is that your cassette must reflect what kind of rides you intend to use it for? loaded touring? flat racing? moutain racing?

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An 11-tooth cog is significantly less efficient than a 12-tooth one, even without the increased wind resistance at that speed.

See the following in depth article "On the efficiency of bicycle chain drives"

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I personally never use my 12 cog: even sprinting I can go faster in the cog maybe one or two down. I tend to naturally ride at quite a high cadence (often over 100 rpm) even when cruising, live in a fairly flat area, and I'm just an average rider who isn't going to do an average speed faster than 30kph over any reasonable distance. For me, filling in gaps in the gear range is more important than having top end speed. Even when I've ridden in hillier areas I find bike handling is more of a limitation on descending speed than my gear ratios.

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