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I am taking delivery of a new bike soon, a 2009 Specialixed Roubaix Pro and it comes with a 34/50 crank and a 12-27 cassette. I will be able to change out parts and I would appreciate everyone's comments on the gearing. The bike it is replacing had a 39/53 crank with a 12-25 cassette and I was conemplating replacing the cassette with a 12-23 to get the 18 cog.
I rarely used the the 25 and only used the 12 on down hills and the occasional out of body sprint experiences.
My thought is to keep the compact crank and go with a 12-23 cassette. Does this make sense? this will give me a 109.5 inch top gear which is slightly taller than than the 107 inch top gear i am used to (53-13), it will give me nice one tooth steps until I get to the climbing gears of 21 and 23. I usually climb longer or steeper hills in 39-21 which is 48.8 inches and the compact would give me 47 inches at 34-19 and i would have two easier gears after that.
My questions are does this compact set-up make sense? Should i just stay with the 12-27? Does anyone else use the 12-23 in a compact set-up and what are your thoughts? Should i go with a regular double?

Thanks everyone
 

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my roubaixx runs sram compact 11/26 rear most of my climbs are mountain passes, I need the 26 on som but not all mountains but nice to have it there. i want a 52 big though for long fast descents. I am spun out around 42 mph.
 

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I’m a mono-cadencial *****, so I love having a near-straight block cassette. My 50/34 is mated to a 13-25 10sp cassette, so your potential setup makes sense to me. I used a 12-23 cassette for 18k miles until installing the 13-25 a few months ago.

Having used a compact crank with a 16t difference between small and large rings for 4 years, there’s no way I would go back to a conventional setup.

You’ve been comfortably using a 53/39, though, so you can always install 52t and 36t chainrings on the compact crank. Whether that’s simpler than replacing the compact crank with a conventional crank is up to you.

Enjoy the process.
 

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If you are happy with the standard double and it gives you the right gearing for the riding that you intend to do, then it sounds to me that you have nothing to gain by switching to compact gearing. So I say stick with the standard double and choose a 12-25 or 12-23 cassette as you see fit (you can always easily change the cassette later). I don't really see the sense in switching to the extra gearing range that a compact can give you, but then narrowing it back down again to what you are used to with a 12-23 cassette. You will pay for this with the increased gap between the chain-rings and more front shifting or cross chaining.

However, if you are looking for significantly lower gears, then compact is a good way to go. I ride a 2009 Tarmac Pro with a 50/34 crank and 12-27 cassette and it is perfect for the hills I ride and the cadence I like to keep.
 

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Getting a compact didn't make sense in the first place if you didn't need a 53/12 or 39/25 very often. A compact is intended to increase gearing range for those who need more low gearing.

A 53/39 with a 12-23 would have been the smartest choice, since you get the 18T cog and skip the 25. The 53/39 requires less cog shifting after every chainring shift.

With a compact, I'd either get an 11-21 or 11-23, since the 34/21 low would be the same as a 39/24.
 
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