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I just bought a bike frame (Eddy Merckx Corsa 01) and am contemplating parts to build it up. Nothing other than a standard 53/39 crank entered my mind until I looked at the poll on this site. Compact cranks seem to be getting popular, and I ain't getting any younger, so why not.

If I get a 50/34 crank it seems like I'd want the smallest cog in the cassette to be a 11 rather than a 12. What about the biggest? What is equivalent to a 27 tooth cog on a 39 tooth chainring? 23 or 25? What are you guys using? I do a range of riding from fairly hilly to flat as a pancake. I guess I could always buy a second cassette.
 

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11-25 will get you closer to the 39 equivalent. I like an 11-23 for the narrow range between each cog though.
 

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I'm waiting for my compact crank and I'll stay with my 12-25 until it wears out. I'll be targetting a 11-23 when it need replacing unless I love the 25 for very steep hills. For you, I made some calculations and an 34x23 gives you a slightly higher ratio than a 39x27. If you want a slightly lower smallest gear, go for 11-25. The closest would be a 11-24 if it was doable...
 

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Everybody needs spare wheels.
Wheel 1) 12-23
Wheel 2) 12-25

Unless you race, you don't need an 11 with a compact.
 

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riding on 12-26 (force cassette) on my compact crank (rival crank)
 

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I run 50-34 x 13-23 9-speed.

16-17-18-19 are nice big ring cruising gears for flattish terrain and the extremes of 34x23 and 50x13 match the 52-42 x 14-28 which was comfortable in the 6-cog era.

I'd add a 26 on the big end before I put a 12 on the small end.
 

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An 11-23 is a good combo with a 50-36. Not that you'll ever really need the 11, but it does give a better chain line to the gears you will use frequently.
 

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StillRiding said:
An 11-23 is a good combo with a 50-36. Not that you'll ever really need the 11, but it does give a better chain line to the gears you will use frequently.
With the compact the big ring works better and the 11 doesn't help chain line.

Most people would be better off with an 18 instead of an 11.

50x19/36x14, 50x18/36x13, and 50x17/36x12 are all the same comfortable cruising gears for terrain somewhat either side of flat although the big ring has more left for downhill and enough for somewhat uphill and the 11 isn't helping chain line in that case.
 

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I'm still in the air weather to go with a 11-28 or a 12-27 on my next bike. It will have a 50/34 up front. I currently have a 50/34 by 12-25 on my bike.

Peace :cool:
 

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Drew Eckhardt said:
With the compact the big ring works better and the 11 doesn't help chain line.

Most people would be better off with an 18 instead of an 11.

50x19/36x14, 50x18/36x13, and 50x17/36x12 are all the same comfortable cruising gears for terrain somewhat either side of flat although the big ring has more left for downhill and enough for somewhat uphill and the 11 isn't helping chain line in that case.
I cruise in the small ring since I prefer to not shift rings and cogs to go uphill. When I shift to the big ring, it's usually when the load is lighter as in starting a downhill or downwind. I can easily spin a 36x14 to over 20mph, which is a good chain line and a good cruising speed for me.
 

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MR_GRUMPY said:
Unless you race, you don't need an 11 with a compact.
Wrong.

I routinely like to wail down long mountain descents in my biggest gear combination. When my smallest cog was a 12 tooth I was spinning out regularly.

I can still get the 50-11 combination to spin out occasionally (somewhere around 49-50mph) but it happens far less frequently since I switched to the 11.

fwiw I really like the SRAM 11-26 cassette with compact chainrings.
 
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