MTB 2x9 Build

  1. pa biker

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    I know it's not as sexy as a 2x10 build, but have a 9spd XT rear deraileur, 9spd chain, and XTR shifter pods already.

    Here the scoop:

    I've been single-speeding pretty much exclusively for the past several years and run 34x20 in the off-season or on hilly stuff and 34x19 the rest of the time. In the winter or when I have mechanical issues, I break out my Moots which has a 1x9 drivetrain (34t front, 11x34 rear). There is nothing that I cannot climb with that gearing (that is that others can climb) so I'm good at the low end with the 1:1 gearing, BUT I want to go faster.

    So I am building a Specialized Stumpjumper 29'er I have laying around and would like to have 2x9 gearing. I intend to use the same rear cassette (11x34), but need to figure out which two chainrings to buy for the front and there are alot of options:

    26x38
    28x40
    30x42
    30x44

    It seems like the 30x44 would be the logical option. Am I missing any downside on that choice?

    Posted 5 months ago

  2. jpouchet

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    Depends upon how Fast is fast? I'm still slugging around a 3x9 and know that my next ride will probably be a 2x10. The 1x pie plate doesn't appeal to me.

    A 34/44 combo is a solid starting point though it will start to spin out around 44 mph. A 34/46 combo gives a little more range or lets you spin easier. Not everyone likes cadence north of 110.

    That Stumpjumper should build out really nice. Good handling frame.

    Posted 5 months ago

  3. jmdirt

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    There are a lot of "depends": depends on where you ride most of the time, depends on the watts you put out, depends on the RPM you like to spin, depends on wheel size (29)...

    If you feel like 44/30 wil work well go for it but don't be afraid to go 42/30 or even 40/28 for a 29er.

    I had 48/36/26, then 46/34/24, then 44/32/22, then 42/32/22, now 42/32 (on 26"). Each time that the big ring became "less big" I was worried that I would be spun out on certain trails. While I certainly spin more RPMs than I used to, it feels just fine. I am moving to 29" for next year and will probably run 38/26.

    Posted 5 months ago

  4. pa biker

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    It is a 29'er. WTF is this Shimano Dyna SYS? Does that mean, chain, cassette, and rings all have to be the same?

    Posted 5 months ago

  5. Keith RIchards

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    I would go for the 42 myself. 42/11 is plenty of gear on the top and you get a touch more use of the big ring.

    It is his word versus ours. We like our word. We like where we stand and we like our credibility."--Lance Armstrong.
    Posted 5 months ago

  6. Jah

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    Quick guide to Dynasys

    1. Road 10 speed derailleurs and shifters are completely incompatible with mountain (dyna sys) 10 speed derailleurs and shifters. The cable pull by the shifters is different for both front and rear.

    2. Nine speed rear derailleurs will not work with 10 speed mountain rear shifters. They will however work with road “flat bar” 10 speed rear shifters. Dyna speed shifters pull twice as much cable per shift as 9 speed shifters, so if you use a 9 speed derailleur it shifts two gears for every one push.

    3. Dyna sys 10 speed rear derailleurs cannot be used with 9 speed shifters. Road 10 speed derailleurs can be used with 9 speed shifters.

    4. Nine speed front derailleurs can be used with 10 speed front shifters, but do not work optimally if used with a 10 speed crankset. Nine speed front derailleurs and cranksets can be used with 10 speed chains and front shifters. A nine speed shifter can be used to shift a 10 speed dyna sys front derailleur.

    5. 10 speed road chains are different from 10 speed mountain (dyna sys) chains. The dyna sys chain is a directional chain that is made to shift better with 10 speed mountain drivetrains.

    6. 10 speed road cassettes and 10 speed mountain cassette use the same sprocket spacing.

    more info: http://blog.performancebike.com/2011/01/28/spin-doctor-tech-tip-10-speed-mtb-drivetrain-compatibility/

    Posted 5 months ago

  7. longslowdistance

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    Jah, are you aware of a problem using dyna-sis rings and cassettes with other Shimano or SRAM chains and derailleurs?

    Posted 5 months ago

  8. Jah

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    basically, the cranks are interchangeable between 9 and 10 speed. I am also aware of folks mixing 10 speed stuff like chains and cassettes from other companies with good results. Shimano always tries to hide this part of the compatibility equation:)

    Big thing is the rear derailleur has to match the shifter and the number of gears that they are going to work with

    as far as the 2x crank - finding a 104 ring smaller than a 32 might get tough.

    Posted 5 months ago

  9. jacques_anquetil

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    Yes, go smaller rather than bigger: 38, 40 or 42. 44 is big for a 29er. I've got the 40-28 XTR option and it is great for range. I can ride most anything in the big ring with the 11-36 and only shift to the inner ring for the steepest stuff.

    Posted 5 months ago

  10. Andy

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    Gearing is so terrain and rider specific. I'm running a 38 x 11 as my big gear on my 29er and I only spin out at around 50 kph. Only long road downhills allow me to do that. I need the 26 x 36 low gear too. Most of the "racy" 2x10 chai rings have their own specific bolt diameter. SRAM is specific to SRAM. Shimano to Shimano. Not sure about the race face. The trail XTR double is standard triple sized. Of course there are other chairing manufacturers out there too.

    Lance who??
    Posted 5 months ago

  11. pa biker

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    Sounds like i'm looking for non-Dyna SYS, 9speed, Shimano 42 and 32 rings for up front and just stay with the 11x34 in the rear.

    Posted 5 months ago

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