Cyclocross - XTR front derailleur, 105 brifters? (I know this has been discussed before)...

...I just couldn't find definitive answers when I searched. Trying to figure out how to build my cross bike up - if I use an XTR front derailleur with 105 brifters will it work?

I'm using a mountain crankset so the large ring will be a 46 I think.

Thanks.

I think it will work fine. I used Ultegra barcons with my Deore LX RD without issue. I now run Forte brifters with the same RD and it works flawlessly. Same setup with a 44t big ring and an Acera FD with the granny position locked out. I'm fairly certain that with Shimano if you match speeds, you'll be fine.

With rear derailleurs you can mix and match road and mountain parts with no problems. Front derailleurs are a different story. The pull ratio is slightly different.

I've got an XT front derailleur set up with Tiagra shifters on my commuter. It was very tricky to get set up, but I was able to make it work tolerably well. I get a bit of chain rub when using the big chain ring with the small cog or the small chain ring with the big cog. (Notice: these are not the cross-chaining combinations...these are the ones that are supposed to work.) It shifts perfectly, though. Having an inline barrel adjuster is critical to making this work.

If you're going to use this for cyclocross racing, you could remove the small ring from your crankset and set it up as a double. You'd have no trouble with that at all (except that I hear 105 triple shifters have a nasty habit of breaking if you try to force them into the missing gear, so be sure to use the top two and not the bottom two).

I believe JTek makes an adapter that is supposed to fix the pull ratio problem, but I've never tried it. I've also wondered if using a road front derailleur with the MTB cranks would be a better solution, but I haven't tried that either.

Thanks for the replies.

I have 105 double shifters, thus I would plan on taking the small chainring off the crankset to make it a double as well. Would this make things work better/worse?

Alternatively, how much of a disadvantage would I be at in a race if I just rode the 34t chainring and forget about the front derailleur? I have a 12x23 in the back.

The double setup should work perfectly (aside from an imperfect chainline), but I think you'd probably be OK with just the 34-tooth ring. That would get you over 23 MPH with a comfortable spin, and how often do you go faster than that in a cross race?

Haha Andy_K this is my first foray into cross so I have no idea!

UPDATE - I can get my hands on a dirt cheap pair of old 105 cranks - with a 39 tooth small ring. Would using this be a better plan then the mountain cranks?

I kind of like the idea of doing a 1x9 setup...its more simple.

I see you're from Beaverton - I'm originally from Ptown myself.

The 39T 1x9 setup is very common in cross. You'll need something to keep your chain from dropping. You can use a bashguard in place of the big ring (Portland made (http://www.bbgbashguard.com/)!) and a chain watcher (http://www.universalcycles.com/shopping/product_details.php?id=6716).

That said, I can only think of two times when I could have spun out a 34-12 combination, and both times were going down hill on pavement. Faster riders may top 23 MPH on grass, but they can usually spin pretty fast too.

Is 39x23 going to be too high for my lowest combination? Or at that point am I better off running up a hill anyway? Sorry for all the newbie questions, I appreciate that you're taking the time to help clarify things for me.

I'll do 39x27 and still ride up a hill over running. Even if I'm no faster than the runner up the hill, I gain time on the remount either because the runner slows down or at least while he's remounting I've upshifted and started accelerating.

Is 39x23 going to be too high for my lowest combination? Or at that point am I better off running up a hill anyway? Sorry for all the newbie questions, I appreciate that you're taking the time to help clarify things for me.

39x23 is a bit high. When I've got a course that I know has hills, I use my bike with a triple. A lot of people say that at some point a lower gear is slower than running, but I've ridden past runners in a 30x27 gear and they spent more energy than I did getting up the hill.

If I were going with a single 39T ring (which would work well for most courses), I'd probably want a 12-27 in back.