Cyclocross - Gearing Q's: 39T x 13-29T, Short Cage?

I'm building me up a bike for my first season of cross. What do you guys think about the gearing above? 39T for the front is the lowest I can go as I'm using standard cranks. The high-end might be low but I'm not really too concerned about contesting.

Will a short-reach Centaur derailleur work for this chainring/cassette configuration?

Thanks.

I think the range is fine, some might say too low. I run 39t by 11-25 myself. I found that switching to a 39t ring from a 42 allowed me to stay in the middle of the cassette more during races, if that makes any sense.

The short cage centaur should be ok with a single ring, but 29t might be pushing it for clearance.

You should be good. One of my bikes has a 36 & 46t chainring combo with a 12-27 cassette. It has a short cage Shimano 105 RD and it operates perfectly.

you can run 13-29 on a short cage with 46/36 (maxes out derailleur capacity) so single ring definitely

Hmmm... thanks all.

justinb, you've encouraged me to give 12-25 a go. I have it on hand and will try it out to begin with. If it's too tough at race pace, it's good to know I can run up to a 13-29 with few consequences.

As a matter of comparison; how much do you way and how do you take your hills? I weigh 145 and have a low threshold for steep climbs (12% and up). I think most of our cross races out here are on the flat side.

I ran a 42x(12-17) last season and was fine for both flat and hilly courses. There usually aren't long climbs in CX and the short climbs can be easier to run up instead of ride. I prefer a closer ratio instead of a wide range in cross.

Hmmm... thanks all.

justinb, you've encouraged me to give 12-25 a go. I have it on hand and will try it out to begin with. If it's too tough at race pace, it's good to know I can run up to a 13-29 with few consequences.

As a matter of comparison; how much do you way and how do you take your hills? I weigh 145 and have a low threshold for steep climbs (12% and up). I think most of our cross races out here are on the flat side.

I didn't intend to specifically encourage you to do that, but simply tell you my experience: I had no problems with it either in CX racing, using that bike on some beginner/intermediate singletrack, or on the roads (it does get a little bit spun out riding with a group or on paved descents).

I'm 150, and prefer a high cadence as opposed to pedal mashing.

Might as well give it a go if you've already got it on hand. Having another cassette around like a 13-29 adds versatility... there won't be much you can't climb with a 39/29 gear and fat CX rubber.