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  1. #1
    mtbr member
    Join Date
    Jul 2014

    I want 42-28 or 44-30 double MTB 10 speed crankset--best option?

    Converting an old 26" MTB to a double setup with all-new 10 sp Deore drivetrain. Ideally I want 44-30 crankset, but the only one I can find is XTR M985, which is too expensiive. 42-28 would be acceptable. What are my best options? I prefer Shimano.

    1. Buy FC-M615 Deore 40-28 crankset and swap out the 40 for a 42t ring from deore/SLX/XT triple crank. (Will this work?). Use Deore FD-M615 front derailleur.

    2. Buy SRAM x5 or X7 42-28 crankset. Do I need a SRAM front der for this or can I use the Shimano M615?

    3. Buy a triple FC-M610 crankset 42-32-24, remove the 24t and 32t, and buy a 28t ring, and run it as a double. Would this work with a double M615 front derailleur? Chainline issues? Can I run this on the inner-middle positions instead of the middle-outer?

    4. Use an old 110 BCD crank and buy 44-30 chainrings for it. Would this work for 10 speed? What rings would I need?

    Any help would be appreciated.

  2. #2
    mtbr member
    Join Date
    Jul 2011
    I assume you really know that you want a 44T/42T ring and that for your purposes a 40T/11T high gear just isn't enough.

    Option 1 will work fine. I suspect you can find a Deore/SLX 10sp chainring for ~$20.

    Option 2 will also work fine. Technically I suppose Shimano might claim a slight loss of shifting quality when mixing and matching chain and chainring brands, but nothing I think you could notice. The front derailleur can be Shimano.

    Option 3 might be tough but should be workable. You will have to run it as inner-middle because the smallest chainring you can get to fit on the middle (104BCD) position is 30T. Then the question is whether a 42T on the middle position will clear your frame - you might need to space your bottom bracket a little further out on the drive side to get the 42T to clear your frame. Doing so would also help with chainline.

    If you go with Option 3, you should get an M610 triple front derailleur, to match your crankset. Because of the difference in chainring spacing between the Shimano double and triple cranksets, there's a good chance the M615 front derailleur will drop your chain inside when downshifting to the 28T, even if everything's set up correctly. You will want to set the shifter pod to the 2x setting, though.

    Option 4 is possible but I would not recommend it. You could find 74mm BCD 28T and 110mm BCD 44T rings - Dimension and I think Sugio are still making them. They should work fine with an 8/9/10sp chain. The downside is that the M610/M615 cranks are just much better than an old square-taper 3pc crankset. And you may have trouble finding rings further down the line. I don't know how well they'd shift, but I'm sure you could get it working.

    I would personally stick with option 1 or 2, probably 1 if I wanted to stay all Shimano. There are also 9-speed 44T chainrings you could use, which would work fine (though shifting between a 28T and 44T might be rough - I'm not sure there).

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