Cyclocross - building a 1x9 cx...need some suggestions on parts..

After watching some cx youtube vids I got excited for the fall season and want to try it out. I decided to look through my parts bin and see if i have enough parts to build a cx. I'm thinking 1x9. What chainring should i go with if i have a 12-25t cassette? I know this might not be a favorable cassette, but like i said, parts bin. Also, what is a better option for a rear derailleur, a mountain or road one?

thanks!

I'm running a 12-27 with a 42 in the front. My current RD is a XT that I had in the drawer. Everything works for my tests so far. First race is in a couple week so I'll know more after that.

You don't need a mountain der if the cassette is 12-25. For the chainring, 39t (parts bin!) should work well. A front der can work fine as a chainkeeper. Just mount it as low as possible, and set the limit screws so it doesn't rub the chain.

couple more questions...
if i use a triple crank...can i use a short cage 105 derailleur(1st generation)? Maybe ill have too many redundant gears. So if i stick with the original plan of having 12-25 in the back, and my middle chainring is a 39T it looks like i might be golden. Do I need to consider bb length? 109 vs 113(or is it 118?)?

I'm running a single 42 with an outer ring guide and a 12x27 in back using a standard Dura Ace RD-7700. Perfect tension and shifts and no drops after several hundred trail miles. Pretty bulletproof setup.

42 with an 11x30 in the rear.

couple more questions...
if i use a triple crank...can i use a short cage 105 derailleur(1st generation)? Maybe ill have too many redundant gears. So if i stick with the original plan of having 12-25 in the back, and my middle chainring is a 39T it looks like i might be golden. Do I need to consider bb length? 109 vs 113(or is it 118?)?

Use this: http://www.sheldonbrown.com/gears/

Be sure to put a value in under Gain Ratio, the data will provide road speed @ your crank RPM.

This is great for selecting a cassette & chain ring combinations. Put in your current data, too; its a reality check.

Michael

couple more questions...
if i use a triple crank...can i use a short cage 105 derailleur(1st generation)? Maybe ill have too many redundant gears. So if i stick with the original plan of having 12-25 in the back, and my middle chainring is a 39T it looks like i might be golden. Do I need to consider bb length? 109 vs 113(or is it 118?)


Go w/t Sugino 103mm track bb available from http://www.universalcycles.com It'll give a straight chainline in your climbing gear. I've done several of these conversions. Not for cx at this point, but it works really well for road, commuter applications. Would suggest to use an unramped cr such as a Rocket Ring(cheap) or Sugino Messenger or Vuelta TT(not so cheap) along w/your front der, as suggested. The combo will virtually eliminate 'chaindrop'. Also, if you don't mind spending the extra jack you can get bashguards. They REALLY help w/chaindrop in addition to protecting your chainring. Also, shorter(165mm) cranks will give better torque for climbing, though you'll lose a little in your sprinting top end. Bulletproof BMX cranks are cheap, solid and available from http://www.bikepartsusa.com. They match up real well w/t Sugino bb.