So yeah, I'm thinking of doing what a few others do and build up a cross bike as my do it all cx-road bike. I currently have a dedicated road bike and am thinking of selling it. I race full seasons of cross country mtb and cx and only do maybe 2 or 3 road races. So it seems like it would make more sense to have a cross bike that I can train on in the winter, do a couple of road races with and race cross on in the fall/winter.
Obviously the gearing question comes up. So I was wondering if I went this route what, if anything would be wrong with having a crankset with an extra drive-side crankarm and rings. During cross season I could use the appropriate gearing and during the off-season, just swap the other arm/gears on there. Anyone think I would possibly need a longer chain for the "road" setup since it has bigger rings? Anything else that I would need to worry about? Thanks.

Why not just swap the chainrings? This will cut down on the wear & tear of crank removal. Plus swapping cranks would need the purchase of both cranks.

I don't know about the chain length but why not have two chains anyway? I always size them at the optimum length for the cassette/rings.

I have one cross bike which is also my one road bike. I run road compact (50/34) during the off-season, and single ring (42t) during the season. No need for changing the crankarm. (Salsa makes a chainguard in 110bcd.)

Last fall when I switched to the single, I shortened the chain using a Sachs link, then when I switched back to the double, I bought a new chain. (New chain once a year is hardly excessive IMO, especially after a season of mud and grit.)

yeah, i guess just swapping chainrings would make more sense, didn't really think about the versatility of a compact.

You'll also have to re-adjust the front derailleur for the different big ring. Just switch chainrings, you don't need a seperate crankset.

I fall into the category of switching out cranks (and rear derailleurs, and front derailleurs, and...) 'cause I have most of an extra DA group laying around. In the spring, I switch over to road gearing and in the fall, I switch back to cross (XTR) gearing.

Yeah, I *could* go with extra rings and cogs and keep the XTR on, but the DA shifts so much mo bettah.

Now the conundrum is to go 10s or not?! If I do that, the component swap may or may not happen... I have rings up to about 54t for a compact, so chainging rings will be easy. They're just in Phx!

M

I swapped out my 36-46 CX crank arm for a compact 34-50 road to do a rough road race. It's not hard to do, but remember that you will likely need to adjust your front derailleur up and down on the seat tube for it to shift well with the different big ring sizes, and chain length may be an issue- you can suck it up and get a second chain, or live with the fact that you need to be more careful to avoid the extreme hi-lo gear combinations, not a problem until mid-race tunnel vision makes you stupid. FWIW, for road racing anyway, I've been on standard 39-53 for a long time, going to a 34-50 compact is a little awkward, I don't like the large drop and found myself shifting the front more than I like. However, a 36-50 compact is really nice, I never really need the extreme of the 34 (at least until I'm way dropped like a boat anchor out the back), the 36-50 shifts very well, I don't miss the high gear (I'm not a sprinter, and my cadence is on the high side anyway) and the best unexpected part is that I'm in the big ring more through the rollers that are typical of my mid-atlantic road races, more useful gears for me, same for racing crits, I love the 50t big ring more than a typical 52 or 53.

yeah, didn't think about having to move the front derailleur either. I'm on the standard 39-53, so going compact will be a little bit of an adjustment but maybe i'll try a 36 small ring as well. all in all it doesn't seem like too big of a hassle if i only have to do it once a year.