Cyclocross - 1x9 gearing connundrum.

(Cross posted from the mechanics section, since I figure y'all will have some more specific advice on the racing side.)

Hey all -- I'm trying to figure out what to do with the gearing on my Cyclocross bike. I use it for offroad rides, and also commuting, and I intend to eventually use it for CX races when I feel a little more comfortable with the idea. :P Here's my issue. It's an Ellsworth Roots frame, and I'm running a 1x9 setup. Right now I have an 11-23 cassette and a 34t chainring -- which is a fairly low gearing, so I can spin out 34/11.

I'd like to run something more like a 12-27 / 42t, but the issue is that a 34t is basically the biggest ring that will fit on the inside of the crank spider and have enough clearance between the ring and the chainstays. If I put the 42t on the outside of the spider I end up with a sub-par chain line -- it just doesn't really line up right, and the bike is noisier, has rougher shifting, etc... it's very unsatisfying.

The question: How can I put a larger chain ring on without screwing up my chain line? Is there any way to space out the cassette so that it properly aligns with the chainring when it's on the outside of the crank spider?

Other relevent details: It's a narrow BB, which is one of the reasons that a 34t is the absolute biggest small ring I can get on the inside of the spider. It's a 5 hole FSA crank. Here's a pic of the bike, hopefully it has some useful details:

http://i37.tinypic.com/de7hg7.jpg

Thanks! :)

New, BB with longer spindle is your answer. Many places recommend using a triple BB to get the best chainline. I think that is 118 but not sure.

Looks just like the FSA Carbon Pro ISIS compact crank on my road racer. Am I right? The BB spindle would be 108mm for a road double. The chainline would then be about 2.5mm inside out on the inner ring and about 2.5mm outside in on the outer ring. I personally don't notice a difference in shifting from either position. I suppose you could also have a 113mm spindle which would put the chainline dead straight in the inner position but 5mm outside in from the outer position which is the same as the big ring on a road triple.

Can you measure or otherwise verify what it is?

In any case, I'd probably switch to a SRAM 11-26 cassette with a 38 or 39 tooth chainring. It would get you a higher highest gear than a 42-12 with the same lowest gear and the same chainline you have now.

Just my 2¢.

Front derailleurs exist.

It is a 108mm BB, but it's an older Octalink bracket. I really like the idea of the 11-26 cassette with the 39t chain ring, I'm going to look into clearance and such. Thanks!

Front derailleurs exist.

HA... word. I never understood the appeal of 1X# setups since you by definition will have a crappy chainline on at least 1/2 of the cogs.

HA... word. I never understood the appeal of 1X# setups since you by definition will have a crappy chainline on at least 1/2 of the cogs.

Not at all. It isn't the same as cross-gearing on a triple or something.

You can try putting a couple of spacers between the BB shell and the frame. If the LBS doesent know what you are asking for just ask for some cassette spacers, like the ones that come with Mavic wheels. Hopefully 1 or 2 of these will work for you. If you have an aluminum spider you might try taking a millimeter or 2 off the inside of it as that would move the chainring outboard as well. You could probably get a machine shop to do that for fairly cheap. I suppose you could do the same thing to the chainring you want to put on as well.

Not at all. It isn't the same as cross-gearing on a triple or something.I agree. I run a single ring for racing, no problems at either end of the cassette.

But I don't really understand why you are running a single.

I don't really understand why you are running a single.

I like the simplicity of it, and I guess I'm just not committed enough to be swapping out parts all the time for my offroad riding. :P

+1 on the 42. That's an ideal size for what you want to do (although the 39 isn't far off either. Although I can't off-hand tell you what width you need. I do believe the answer lies in changing out your current bottom bracket for one that's wider.

I also second the idea of running a single chain-ring up front for simplicity's sake. A bashguard and chain watcher come in handy for that sort of application as well. I think you're on the right track...

Yep, I have a bashring on the outside of the crank, as well as a dog fang. I really like the setup, I just can't seem to fit a very large ring on the inside of the spider. I'm using a 108mm BB, so if I went to the 113, I'd get 2.5mm on each side -- which is enough for like a 36 or something. Pretty underwhelming.

Does a different crankset have any effect?

Yep, I have a bashring on the outside of the crank, as well as a dog fang. I really like the setup, I just can't seem to fit a very large ring on the inside of the spider. I'm using a 108mm BB, so if I went to the 113, I'd get 2.5mm on each side -- which is enough for like a 36 or something. Pretty underwhelming.

Does a different crankset have any effect?

I have a friend who has your same frame, next size down, and he runs a 42 with no problems. I will ask him which crank he has next time I see him. You might just email the frame maker and ask them what they recommend.