Compact Crank Set with 12-27 (10 sp) Cassette?
Need some advice! Will I be wasting time getting a 12-27 (10 sp) cassette with a compact crank set? Advice, experience, or thoughts on this kind of a set-up?
I'm modifying the road bike for triathlons. Training rides and courses are hilly with some long climbs. One course is a 9% grade with a small section at 12%. I'm a "larger" cyclist with the time clock seeming to tick faster and faster that has some "difficulties" with hills! (Hmmmm size might be one issue!) I know I have several alternatives including:
1) Only go down hill
2) Avoid the hills altogether
3) Loose weight (which I'm doing already)
4) Change the bike set-up (cassette and cranks)
I'm opting for choices 3 and 4! The fun really begins after you have crested the hill! Downhill is a kick . . . but, ya gotta climb the hill first!
THANKS for your CONSTRUCTIVE thoughts and suggestions!
Up on the Down Side
I have a 50/34 compact and a 12/27 cassette in the back. It's a great setup for riding steep hills if you need that extra bailout when the grade goes over 10%.
If you ride flat to rolling terrain, you'll probably find you're in the big ring most of the time. The 34 really is only for climbing or for a really tough headwind. The spacing is really wide, so there is not a lot of microadjustment as you would get with a 53/39 with an 11/21 or 11/23 on the back.
You can combine a compact with a 12-27 OK but there is no way anyone here can know what your gearing needs are. It would really help if you could do some math comparing the gearing that you've been using with the setup you are considering. Calculate the lowest gear inches you need to climb the difficult hills you anticipate while maintaining a good cadence. You can use an online gear calculator or you can use the simple formula: number of teeth on chainring / number of teeth on cog X 27. It really doesn't matter which way you do it since you're only making comparisons,
ie. a compact with a 34 tooth inner chainring and 12-27 cassette gives you a lowest gear of
34 / 27 X 27 = 34 gear inches.
A typical triple with a 30t smallest chainring and 12-25 cassette gives you 30 / 25 X 27 = 32.4 gear inches.
The nice thing about Shimano's 12x27 10-speed cassette is that it has exactly the same cogs from 12 through 21 as their 12x25 and only gives up the 18T compaired to the 12x23 cassette so you are not sacrificing closely spaced smaller cogs to get the 27. Go for it.