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  1. #1
    Happy Trails
    Reputation: Scott In MD's Avatar
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    Smallest Ratio (Best Climbing) For 120mm/80mm BCD Cranks

    I'm considering a Cannondale 29er with a 120mm/80mm BCD crank based on the Sram XX design. It comes stock with a 39/26 chainrings. By my math, in the lowest gear 26/36 (0.72 ratio) I'd be giving up TWO climbing gears versus the 3X9 granny ring on my current Titus RX29 with 44/32/22 up front and 11-34 cassette, and 0.64 climbing ratio.

    Wow, I don't know that I can spin a 26 tooth small chanring on some of my toughest climbs


    Before I consider a different bike with 104mm/64mm BCD >>> 38/24 chainrings, does anybody have insight on improving the climbing ratio?

    Can I get 38/25 chainrings for 120mm/80mm BCD cranks?

    Or... can I just change the spider to 104mm/64mm on a Cannondale SL crank?


    Thanks.
    Last edited by Scott In MD; 10-09-2012 at 09:29 PM.

  2. #2
    29er
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    that is not so much of a loss, i went 1x10 and don't miss the low gears

  3. #3
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    Agree with Dan GSR. I went 1x10 and lost the bottom two granny ratios. You'll miss them for about 3 rides until you realize your stronger in the legs than you thought you were.

  4. #4
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    What gear size are you running up front on 1x10?

  5. #5
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    33 up front with 11-36 in the back

  6. #6
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    I run 26/39 and 24/39 and 22/33 and have 11/36 cassettes in the rear on all bikes. I like the 22 best, but I ride the real nasty rocky technical grinding climbing stuff. I am buildng up a Cdale flash with an X0 with 26/39 with 80 and 120 BCD. I'm planning on droping the 39 for a bash and running it 1x10 with 11/36 in rear. I might be able to live with it becuase I think the build will be sub 24 maybe even 23 lbs. So far I haven't been able to find any gear smaller than a 26 for 80 BCD, but if someone knows about one please post it.
    When the **** did we get ice cream?

  7. #7
    29er
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    i currently have a 28t front 11-36 rear

  8. #8
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
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    I did an extended demo on a 29er with X0 a while ago. I think it had a 26/36 lowest. Normally I ride a 26" with a 22/34 low. I definitely missed the low ratios I lost.

    This is all about you, the trails you ride, and how you ride them. There was actually a particular climb I did several times with the demo bike, an 830' gain in just under three miles. It's funny, writing about it, it doesn't sound like that much to me. But it's singletrack, the surfaces tend to be loose, and it does take a while. That made me miss my granny.

    If your rides tend to be rolling and don't have sustained climbs, I bet you don't miss being able to spin up those climbs as much as you're afraid you will.

    If your climbs are mostly on fire roads with consistent enough traction to get out of the saddle, you may spend a bit more time climbing that way, but you'll get used to it.

    But I really, really value having low gears for a bad-traction climb, or something long enough to wear me down.

    Here's a chart with some minimum chainring sizes. It doesn't include your BCD because, according to Grant Peterson, nobody rides mountain bikes. But there's one higher and one lower, so you can at least bracket it.
    Learn About Bikes with Rivendell Bicycle Works

    I don't think you're finding smaller than a 26.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  9. #9
    official eMpTyBRain
    Reputation: Hawg's Avatar
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    I went from a 26er with a 22X32 lowest to a 29er with 26X32 lowest and never looked back. The 29er also weighs 2.5 pounds more than the 26er did and I am not in any better physical condition than I was before. As already mentioned, you will get used to it fast. I live at the base of a very steep mtn range and climbing it is unavoidable. The 26X32 on the 29er was/is totally doable for me. You'll be motoring uphill faster which is spiritually uplifting.

  10. #10
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    Reputation: Rack Man's Avatar
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    When I built my T-29.....I originally used the 39-26 set up....after a month or so of riding that set up was just too "tall" for me.....I really needed the lower "bail out" gears as I climb a lot (and I'm weak).....I went to the 36-22 combo and absolutely love it....



    RM

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