Let's just start off by saying that the gearing that comes standard on road bikes is just way too high. Seriously, how many of you can truthfully say that a 53/39 with a 12-23 cassette is perfectly geared. If you say this you are either:
A. A Cat 2 criterium racer who lives and races in the flatlands.
B. A small Spaniard climber on a continental team.
C. A delusional wanna-be with blown-out knees.
D. A liar.
Most of us would be much better off with reasonable gearing. The problem is that we either as compelled to use racing gearing or touring gearing. Road bikes now tend to have 50/34 chainrings and a 12-25 cassette. True touring bikes usually employ a mountain bike crank (44/32/22) with a wide range cassette (11-34). We usually need something in between.
With the advent of the compact double crankset, we now have a chance if we want to be fast and have reasonable gearing. How do we do it?
First, let's start with the 50/34 compact crankset. A 50 tooth chainring is plenty big when paired with a 12t cog. This is actually a higher gear than the 52/13 that was a common top gear thirty years ago. If you're sprinting with a 120 rpm cadence in this gear, you'll be going 41 mph. Not many of us can sprint that fast. Including Cat 3 racers.
So the high gear is good, even more than we need. Let's look at the low gear. If we have a 34T small chainring paired with a 23t cog, this gives us 39 gear inches. If you don't know what gear inches are, don't worry. We'll only use these as comparison. Let's move to a 26t rear. SRAM sell a nice 12-26 cassette that's relatively inexpensive. That gets us down to 34.5 gear inches, an improvement of 12%. Okay, much better.
But we've got this one really steep hill...
Okay, how can we get a lower gear. We can change to a triple crankset. That's expensive and adds weight. We can change out the rear derailleur and cassette to accommodate an 11-34. Good idea, but still expensive and maybe a bit of overkill. We can use a larger rear cog. No, the cogs all connected together and they don't make them any bigger that a 12-27. Besides, it says my rear derailleur won't work with a cog bigger than 27t.
Hah! Here's what we'll do. First of all, a short cage derailleur will work okay with a 29 or 30 tooth cogs. A little adjustment may be needed. Second, we can take apart these cassettes. On a SRAM PG950 cassette, these are three screws through the body that can be removed with a 1.5mm or 2.0mm Allen wrench. So if we take apart a 12-26, we have 12, 13, 14, 15, 17, 19, 21, 23, and 26 tooth cogs, assuming we have a 9-speed. I think the 14 is of little use to us. Let's pull that out (along with the spacer) and get a 29T Miche cog. Yes, they do make one and it's only about $8. Re-assemble the cassette to the wheel (don't worry about replacing those little screws) and you're ready to go. Now you have an 11% lower gear than the 26t and a 21% lower gear than the 23t.
I may be the only person in the State of Illinois riding with a 12-29 cassette, but it's certainly much more practical than the 12-23. Now I know I'm not the only person in the country with one, since I set my brothers bike up the same way.
Now you know there are more options for gearing out there. Don't be stuck in a gear too high.
P.S. SRAM has just come out with their new Apex group. With a standard setup, you can have 50/34 paired with a 10-speed 12-32. And if you're willing to swap to the MTB rear derailleur, you can go with a 12-36 cassette. A salute to all of you at SRAM!