I am getting a DA bike with a 12-27 cassette, which I think is probably best for me . . . still somewhat new and with only a double in front (and not a compact) I could use the lower gear. I see that I am essentially getting bigger spaces starting at 17.
What are the pros and cons of each?

I have fairly strong legs, but they are still getting 'biking' stong, but I also live in North Central Indiana which is about as flat as a pancake.

If you mean that "flat as a pancake" stuff literally, I can't imagine why you'd need a 27. I have a 13-26 on my older, D-A bike, and a 13-29 on my newer, Campy Veloce bike -- but we have a lot of rolling hills around here. Most aren't too steep or long, but I'm an older Clyde who can't climb worth beans, so it's what I need.

Out on the flats, though, I'm usually out in the middle of the range, using the 15, 16, 17, 18, 19 depending on which ring is selected up front and how fast I'm going. I virtually never select anything lower than the 19 except when I'm starting up a hill.

If it truly is that flat where you live, I'd suggest a 12-25 at most and maybe even a 12-23. (Take into account if you'll ever be going elsewhere to ride where you may need a lower gear.) Flat often means windy, and by ditching the hill-climbing cogs that you probably don't need, you'll have a more even overall range that will better allow you to maintain the same cadence no matter what your speed.

No, it is not that flat. There are some hills I can find (and will). The main Triathlon course here (Eagle Creek Park) actually has some ups and downs. I think I will be happy with the 27.

I guess the downside is just bigger gaps, so sometimes cannot find the perfect gear.

I climb Eagle Creek Park on a fixed gear with zero problems and I'm old. You really don't need a 27 tooth cog for that course. I've been following your other threads and I suggest you ride the bike first before you decide on making changes...

By the way, as an out of towner that visits IND quite often, Eagle Creek is a great place to ride

thanks. I am not planning on changing a thing for a while . . . more just curious about the setup I have and what people do. More than anything, I am posting a bunch of questions in different areas just to learn more and sort of get a feel for the place. I am like a sponge at the moment.

Hey Greg, a tighter cassette is nice but keep in mind you may end up doing to hilly hundred or other southern IN rides at some point and the 27 will be nice to have. There's nothing wrong with owning an extra cassette and they take just a minute to change. When you do need a new cassette, check out the 105 and Ultegra cassettes. Just a few grams heavier but several $$ cheaper!

I climb Eagle Creek Park on a fixed gear with zero problems and I'm old. You really don't need a 27 tooth cog for that course. I've been following your other threads and I suggest you ride the bike first before you decide on making changes...

By the way, as an out of towner that visits IND quite often, Eagle Creek is a great place to ride

Hey Dave, what kind of gear ratio are you using when you visit our fine city?

70 gear inches. My fixed is 42 x 16. Some of the hills at Eagle Creek are a challenge but I can get up them without walking:-)

I found Eagle Creek this summer( I even bought a year pass). When you are an out of towner and not familar with the local roads, it's nice to have a loop to ride. I've ridden the Mohan(sp?) many times, but it gets too crowded in the summer

awesome advice - thanks. yep, the hilly could be possible in a year or two. Actually, I am sure I will at least ride in southern Indiana - Bloomington most likely as I go down there a few times a year. I am an IU alum and cannot stay away.

The Monon trial is great for running, no so much for biking. As you said, too crowded. The northern part (Carmel) has a speed limit for bikers as it was getting too dangerous.

I wouldn't worry too much about it. Our gearing needs are not only about how strong we are or how steep or long the hills are. Another issue is what kind of shape we are in at the TIME we hit the hill. If you are on a Century and find yourself on a 10% climb that 12-27 may feel good. I keep enugh parts around I can usually put together anything from a 12-23 to a 13-27 in Shimano. I usually ride a 13-26 in 10-speed Campy or 13-26 in 9-speed Shimano (53/39 doubles).

Al

I live in eastern Nebraska, and run a 12-21 on my road machines around here, and that is always plenty, even when I wander over to Iowa and ride in the hills just east of the Missouri River. I would put a 12-21 on the bike, and only put on the 12-27 if you're heading in to some serious mountains.

SPIKE

I live in eastern Nebraska, and run a 12-21 on my road machines around here, and that is always plenty, even when I wander over to Iowa and ride in the hills just east of the Missouri River. I would put a 12-21 on the bike, and only put on the 12-27 if you're heading in to some serious mountains.

SPIKE

I can't believe that you are an "average" rider. A top end of 21 doesn't get me warm or fuzzy, even if the terrain is mostly flat. For me to consider that I would have to be riding on the Bonneville Salt Flats. :)

I wonder why they don't make a modern "Mega-Range" cassette like they did for some 7 and 8 speed stacks, where they have a big jump between the largest two cogs. If I could fabricate a do anything cassette it would probably be something like a 12, 13, 14, 15, 16, 17, 19, 21, 23, 29, basically trading the standard 26T for a 12T on the bottom.

handsomerob

That 12-21 is really nothing to get intimidated by. On flat to flat and rolling it is a perfect cassette. I tend to average about 19 mph to occasionally 20 mph on my rides around here, and it is always a comfortable set up to ride. I love having that 18 tooth cog on the 12-21. I hardly ever retreat to using the 39 X 21, and when I do it is plenty. I ride TOSRV in Ohio between Columbus and Portsmouth, and the 12-21 is perfect for that ride.

SPIKE