Bicycle Mechanics - 1x9 gearing connundrum.

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 relevant 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! :)

You did not mention what sort of bottom bracket/crankset interface you have on the bike. For example, is it ISIS, Shimano or external bearing of some flavor. How wide is the bottom bracket shell. Is it 68mm wide or 73mm wide.

Here's an example of what's possible. First would be a bottom bracket with a longer axle to space the crankset out. Changing an ISIS from 108mm to 113mm would move the rings out 2.5mm (the other 2.5 goes to the non drive side)

At least one year, 1998, the roots came with a 73mm bb shell and a 107mm shimano crankset mounting a 36/46 double.

It's only a matter of matching the crankset choices with the bottom bracket choices to get something that will do what you want.

Or change to a shorter axle and move the crank inwards so that you can run a ring on the big CR side of the crank and get a good chain line.

Or change to a shorter axle and move the crank inwards so that you can run a ring on the big CR side of the crank and get a good chain line.
Yabut ya wanna check crank/chainstay clearance first.

Keep in mind that you can only have a perfect chain line in 1 gear only.
IF you tend to use the smaller cogs the most, adding a few MM to the BB spindle length might actually improve your chain line for the gears you use the most.

It sounds like the frame is not going to let you put a 42 where the 34 is. Your not going to be able to move the cassette out board enough to compensate for your new chainring position. There isn't enough room on the freehub body. Your not going to be able to find a chainring/BB combo to move the chainring in-board enough (you want it where the 34 is, which is too close to the frame).

Here's a suggestion: put your new cassette on, put the 42T on, and set the L limit screw on your RD so you can't shift to the largest couple of cogs. This will give you the chainline you want, but you'll lose your 27 cog. Your also going to need to optimize your chain length. Your putting on a cassette with larger cogs as well as a larger chainring. You'll need a longer chain. Try a longer chain first before setting the limit screw, it may solve your problems.

Cheers,
Good luck,
Tim

RE "Spinning Out"-

Are you constantly spinning out, or just occasionally?
Sometimes, we can get the impression that if we spin out at all, we need higher gears, when in reality, we are just "barely" spinning out.
What's your cadence? If it's under 90, you need to work on that first.
You may find that if you increase your cadence some, you'll also increase your stamina.
Crank length may also be an issue. IF your cranks are longer than "ideal", it can slow down your cadence greatly.
I have one real bad knee. I discovered going from a 175 to a 170MM crank increased my cadence by 22%! That little 5MM was bending my knee beyond it's flexibility, so I was actually having to "lift" that knee "over the top" by pushing down with the other leg.
That 5MM actually works out to 10 MM, since you raise the seat by 5MM.

Just something to consider-

RE "Spinning Out"-

Are you constantly spinning out, or just occasionally?
Sometimes, we can get the impression that if we spin out at all, we need higher gears, when in reality, we are just "barely" spinning out.
What's your cadence? If it's under 90, you need to work on that first.
You may find that if you increase your cadence some, you'll also increase your stamina.
Crank length may also be an issue. IF your cranks are longer than "ideal", it can slow down your cadence greatly.
I have one real bad knee. I discovered going from a 175 to a 170MM crank increased my cadence by 22%! That little 5MM was bending my knee beyond it's flexibility, so I was actually having to "lift" that knee "over the top" by pushing down with the other leg.
That 5MM actually works out to 10 MM, since you raise the seat by 5MM.

Just something to consider-

Shorter cranks. Thats a fantastic idea. This could solve all the problems. You could even go to 165 if you wanted. you won't gain as many "gear inches" as going to a 42T, but it will definitely get you in the right direction.

Shorter cranks. Thats a fantastic idea. This could solve all the problems. You could even go to 165 if you wanted. you won't gain as many "gear inches" as going to a 42T, but it will definitely get you in the right direction.

I had actually gone to 160's for the last 6 months, since I found these to try on sale for $7.49!-
http://www.nashbar.com/profile.cfm?category=600081&subcategory=60001031&brand=&sku=20985&storetype=&estoreid=&pagename=Shop%20by%20Subcat%3A%20ATB%20Cranks

Ironically I took them off today and went back to the 170's. The 160's seem just a bit too short.They'd probably be OK if I didn't have constant stop & go riding conditions, but needing to accelerate every couple blocks, I don't really get to "spin" more than a block or 2. Cold weather & headwinds slows this 60 year old down a lot too!
I' had to change my BB today anyway, so I thought it'd be a good time to try the 170's again. IF I want to swap back, it's just a few minutes time.

I wish I could find some 165's for $7.49! That grass is always greener!