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  1. #1
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    New to Cyclocross and MTB forum-Building first CX help.

    I'm currently gathering components for my first CX bike-

    I will be using Straight MTBars with Avid Elixir Hydraulic disc brakes.

    I plan on using Shimano XTR M980 2x10 shifters

    Question:
    Will the Shimano XTR FD-M985 be ok for the 34/50 front chainrings.

    and the Shimano XTR-RD-M980 Long Cage be ok for the rear Casette?



    Thanks in advance-
    Doug
    Mountain UNI is the bomb-
    Nimbus Unicycles

  2. #2
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    on long cage - should be good to go, I was using it 1x10 (XT long) with no problems.

    Maybe this will help
    Long cage vs. med cage on 2x10? Does it matter?

    I stay in my small ring (34t) on cross bike w 25/12. I am a strong cat 4 (maybe? - should be Cat 3)

  3. #3
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    Quote Originally Posted by scottz123 View Post
    on long cage - should be good to go, I was using it 1x10 (XT long) with no problems.

    Maybe this will help
    Long cage vs. med cage on 2x10? Does it matter?

    I stay in my small ring (34t) on cross bike w 25/12. I am a strong cat 4 (maybe? - should be Cat 3)
    If this bike is for racing, I'd say two things.

    1-get rid of the 50 up front, you'll never use it
    2-a long cage "may" help with chain slap but on a lower bb'd bike, it's also more likely to catch something on the ground and ruin your day

    Depending on your cassette, a long cage might be overkill. For reference, I run the same crank and often a 11-28 cassette with a small cage on my roadie.

  4. #4
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    Agreed on the 50t, you will not ever use it. I run a 39x11-32 and I'm very happy with it, a 36 would be fine too I think. For a 2x10 a 42 and 28 would be good in front. if You're using a 'compact' crankset, you should be able to get a 36, but your 34 should be fine 95% of the time. A 44 or 46t big ring would be usable once in a while, that would be a better choice. With the 34 you should be able to climb most anything with a 28 as your biggest in the rear.

  5. #5
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    Quote Originally Posted by Walt Disney's Frozen Head View Post
    If this bike is for racing, I'd say two things.

    1-get rid of the 50 up front, you'll never use it
    2-a long cage "may" help with chain slap but on a lower bb'd bike, it's also more likely to catch something on the ground and ruin your day

    Depending on your cassette, a long cage might be overkill. For reference, I run the same crank and often a 11-28 cassette with a small cage on my roadie.
    Wouldn't a long cage be more prone to chain slap, That was what came stock with my 3x10 mtb setup

    Somewhere on mtbr is a chart explaining front ring/cassette (biggest ring?) combination for mid/long cage

  6. #6
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    In terms of der options, the rule I've always followed has been related to how many chainrings I'm running.
    3x - long cage
    2x - med cage
    1x - short cage

  7. #7
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    Quote Originally Posted by Walt Disney's Frozen Head View Post
    ...2-a long cage "may" help with chain slap but on a lower bb'd bike, it's also more likely to catch something on the ground and ruin your day...
    A long cage will be more prone to chainslap. Also, BB drop has nothing to do with the rear derailleur height.

  8. #8
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    Thanks for the information- Pictures soon- Powder coating frame and fork this week.

    Will the Shimano XTR-980 shifters work fine with the Cx-70 front deraillure as far as the indexing goes?

    Thanks in advance-
    Doug

  9. #9
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    One more observation re gearing, as mentioned above my cx bike has a 38 in front (I mistakenly thought I had a 39), I raced my 29er mtb at a cx race over the weekend with my best finish (4th) in my cat3 age group since I was in my 20s, which was a long time ago.
    I did the entire race in the middle ring, a 32, with an 11-32 rear, and did not get dropped while drafting on the paved flats. IMO, a 32 front is big enough for cx, - just your 34 will be fine. I used the 32 in the rear a lot more than the tinier gears. If I were to build a new drivetrain for cx I think I'd go 1x with a 32 or 34 in front.

  10. #10
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    so jimPac, i've got a 175mm crank w/34T ring that i pulled off of another SS build and would like to use for a CX build. are you saying that if i matched that crank up with an 11-32 cassette, i should be in darn good shape for most any CX race? if so then would you recommend i use any sort of chain guide or is that not a concern in CX?

    (to explain my ignorance, i'm coming from a nearly exclusive mtb history, the bulk of which has been SS. i have a road bike but only ride it on pavement a few times a year and on rollers in my basement when the trails are too soaked to ride.)

    thanks!

  11. #11
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    Yes, in my experience the 34 x 11-32 would be fine 98% of the time, and if you start to spin-out on a paved descent, just take a short rest. When you encounter some climbing, you'll really be happy to have the low gear. I'm still running 9 speed, and I use an older xtr rear derailleur, an m952. I had a 9speed xt, the common silver one from the mid 2000s, my friend is using it with his 10sp setup. I believe that the bolt pattern on most of the compact cranks is the same as older mtb, which is 110mm if it's 5 bolt, and it's easy to find older 36t chainrings for relatively cheap. I need to look at a gear ratio chart, but I would be tempted to try a 34 x 11-28/11-27, my 38 x 11-32 might be pretty similar for the lowest gear. The cassette would be lighter and I could use a short cage derailleur.
    Of course it also depends on how strong you are in the short sharp climbs.

    Yes, you will want to run a chain guide, I'll look up the one I have a bit later today. I dropped my chain twice last season w/o a chain guide, no drops this year.

  12. #12
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    I was using a cheaper 'third eye' chain guide, but I got this one instead and I think it's better:
    N Gear Jump Stop 31 8mm 1 1 4" Jump Stop Chain Deflector | eBay
    I had to use a longer bolt since my frame has a pretty fat seat tube. I also use an outer ring chain guide.
    Since you're a SS guy, and are probably used to pushing a pretty large gear, you might be fine with the 34 x 11-27/28. For added perspective, on my old mtb 26er I used 24/36/48 x 11-28 forever, and I stayed in the middle ring most of the time, except for the long sustained climbs and sustained fire road descents, both of which are not usually found in cx.

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