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Discussion Starter · #1 ·
I'm thinking about getting some compact cranks for my 'cross bike, an Alan Cross Carbon X-33. I've been road racing for 4 years but last year was my first year racing 'cross. I built the bike up with hand-me down components from my road bike including a 172.5 FSA road crank replacing the 53t for a 39x48 combination. I knew the 48 would be mostly for training on the road but I found that in a race I was always in the 39 up front and 21, 23, 25 cogs out back...hence the idea that if I dropped from a 39t up front to a 34t (or even 36t) I could spend more time in the middle of the cassette, plus I get a little lower gear and be able to sit more on the climbs. Another note, when given the option, I tend to mash a bigger gear, my cadence sweet spot is about 85rpm.
I found a deal on Veloce compact cranks but they only come in 175. My road race bike and my single-speed mountain bike both have 175's and I honestly don't notice the difference, but since my 'cross experience is limited I'm a little nervous about going longer and then regretting it. I've heard that the BB is higher on 'cross bikes so geometrically but is there anything else I need to consider?
 

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What's so great about the middle of the cassette? Riding the inner chainring and the inner portion of the cassette would seem to offer better durability (less cross chaining, larger cogs) than using a smaller inner chainring and the middle of the cassette. You're also wrapping more chain around the chainring/cog, leaving less slack for the RD to try to keep from dropping.
 

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The amount of difference you'll notice between a 172.5 and a 175 is little to none.

That said, i seem to recall that campy uses a proprietary BCD on their compacts (4 holes are at 110, 1 is at 108 or somethign?), that makes different chainrings pretty spendy to buy - if you can find them.

For cx racing, you definitely don't want to go any smaller than 36 - with the exception of heinous mud, in the 36x25 you're probably faster off the bike running. I'd suggest looking into a wider cassette (12-27) and maybe getting a 38 chainring up front, rather than replacing your crankset.
 

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Discussion Starter · #4 ·
So I'll add a little detail:
The middle of the cassette is mostly psychological...if I know I'm outta gears, that's all I focus on. Plus I don't like the idea of launching the chain into the spokes!
Also, I'm in Pacific NW (Seattle) so we get a fair number of sloppy boggy races. I already tend to run my bike more than others but I would like it to be a choice than a necessity.
Finally, replacing the crankset is part form/function part fashion. My current ISIS BB is getting creaky and I've never been super thrilled with the way it fits in the shell. I've also been dying to try an external BB system--either Campy UT, FSA MegaExo or GXP.
Thanks for the info on the Campy BCD, that's good to know!
 

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Discussion Starter · #6 ·
No shame in wanting a lower gear, IMO. What about just changing the cassette to something that has a 27t or 28t sprocket?

I thought about that option, but was concerned that I'd need to swap to a medium or long-cage rear derailler.

I finally realized my primary motivation is getting away from the TruVativ ISIS BB I've swapped around to four different bikes because I don't like it. I realize I could simply replace the BB with something else but figured why not kill a few birds with one order: tryout new Campy UT cranks, see what all this compact gearing is all about, AND get rid of the BB.

Thanks for all the advice!
 

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crestlinefarm said:
see what all this compact gearing is all about
Compact gearing doesn't really apply on a cx race bike. Most folks are running 38-42 inner and 46-48 outer chainrings with a 12-25 cassette. The idea behind compact is to get easier gearing out of a smaller cassette. Potentially you could run a 34 chainring with a 12-23 cassette, but you'll still want something smaller than the standard 50 outer ring. The real concern is that compact chainrings tend to be more expensive and harder to find in cx sizes than standard, 130 BCD rings. As a side note, I just switched my compact from my road bike to my cx bike (and refitted with 38/46) because I didn't like the huge gap between 50 and 34 chainrings (ATMO, if I may, the SRAM 11-26 makes the compact obsolete anyway).
 
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