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  1. #1
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    New question here. SLX Crank 2ring vs 3ring - Chainline

    I am looking at a 9 speed SLX crank to replace my current one. I will remove the ring and put on a 32T or 33T ring. Shimano lists the chainline for the M665 2ring+Bash at 46.8mm and the 3Ring at 50.0mm
    Is there any difference in the crankarms themselves or is this in the rings. I did note shimano has different part numbers for the left crank arms?

    Wouldn't a smaller chain line figure be preferred in a 1X9 setup?

  2. #2
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    I use a 22/34 with a 12-36 and it seems to work just fine. The shifting is good and I only "run out of top-end" when I'm on a downhill fire road or pavement.
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  3. #3
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    The crank arms are thicker, stronger on the double

  4. #4
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    Thr three ring set up provides the best chainline.

  5. #5
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    It's the same crankset...on a triple the chainline is measured to the inside of the middle ring (Shimano) or middle of the middle ring (Truvativ). On a double the chainline is measured in between the granny and middle. That is the reason for the difference.

  6. #6
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    Quote Originally Posted by mtnbiker72
    It's the same crankset...on a triple the chainline is measured to the inside of the middle ring (Shimano) or middle of the middle ring (Truvativ). On a double the chainline is measured in between the granny and middle. That is the reason for the difference.
    Agreed.

    And technically, the chainline of the double is closer to ideal than the triple.
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  7. #7
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    Quote Originally Posted by shiggy
    Agreed.

    And technically, the chainline of the double is closer to ideal than the triple.

    Nope the chainline (defined as the chain angle off straight) will be the best with a triple ring set up not a double ring set up.

    Simple cause the little and big rings provide a much straighter angle when used properly with the big and little sprockets on the rear respectively.

  8. #8
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    the chainline I am thinking about is a a single ring in the middle. Wil the ring placed in the middle be in a different place in the 2ring(M665) vs 3ring (M660) model?

  9. #9
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    Quote Originally Posted by Grande
    the chainline I am thinking about is a a single ring in the middle. Wil the ring placed in the middle be in a different place in the 2ring(M665) vs 3ring (M660) model?
    No.

  10. #10
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    Quote Originally Posted by jeffscott
    Nope the chainline (defined as the chain angle off straight) will be the best with a triple ring set up not a double ring set up.

    Simple cause the little and big rings provide a much straighter angle when used properly with the big and little sprockets on the rear respectively.

    You need to go measure a drivetrain.

    The chainline of an 8/9/10-sp 135mm hub is ~46mm (center of the cassette).

    The move to 50(or more) mm chain lines is for one reason: Clearance. Not chain angle efficiency.
    Extra clearance between the rings and stays, between the chain and the tire, between the FD and the tire, room for the external bearing cups.

    The wider chainline makes it more likely the chain will drop off of the chainrings to the inside. Decreases the efficiency when using the larger cogs.
    The chain angle does increase when using the smaller cogs but it is a minor issue on a mtb.
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  11. #11
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    Quote Originally Posted by Grande
    the chainline I am thinking about is a a single ring in the middle. Wil the ring placed in the middle be in a different place in the 2ring(M665) vs 3ring (M660) model?
    No difference.

    And yes, a narrower chainline is better for a 1x9 setup. The chain will be less likely to drop to the inside when on the larger cogs and make little difference with the small cogs.

    The limiting factor (other than the amount of BB adjustment) will be ring/stay clearance.
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  12. #12
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    So, the cranks arm are identical and the difference in chainlin measurement come from the fact you measure a triple from middle ring in and a double is measured from the point between the inner and middle. Is this correct?

    Probably make sense to buy the triple then and move the rings on ebay.

  13. #13
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    The crank arms are NOT identical. The double has thicker crankarms and steel inserts for the pedal washers. Also, the Shimano people at the Shimano conference I went to said that putting a big ring on the double will not work correctly as the chainline is different. they are two completely different crank sets.

  14. #14
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    Mr. Fuzzbl,

    I was aware of the steel inserts. Do you think using a 2Ring crankset is preferred when going 1X9?

  15. #15
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    I think it depends on your riding style. Are you jumping off buildings into volcanoes? Then i would go for the heavy duty cranks. But if your riding in fields with butterflies and trolls then the triple would probably be fine.

  16. #16
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    i am thinking for chianline. Sounds like the middle ring will sit in the same place no matter 2 ring or 3 ring. Right?

  17. #17
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    Quote Originally Posted by Grande
    i am thinking for chianline. Sounds like the middle ring will sit in the same place no matter 2 ring or 3 ring. Right?
    According to the Shimano tech manual, the middle and inner ring are in the same position on the 660 and 665.

    If the 665 will not work with an outer ring it would be because the spacing between the middle and outer ring is off, not that the chainline would be wrong.
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  18. #18
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    Good job!

    Quote Originally Posted by shiggy

    You need to go measure a drivetrain.

    The chainline of an 8/9/10-sp 135mm hub is ~46mm (center of the cassette).

    The move to 50(or more) mm chain lines is for one reason: Clearance. Not chain angle efficiency.
    Extra clearance between the rings and stays, between the chain and the tire, between the FD and the tire, room for the external bearing cups.

    The wider chainline makes it more likely the chain will drop off of the chainrings to the inside. Decreases the efficiency when using the larger cogs.
    The chain angle does increase when using the smaller cogs but it is a minor issue on a mtb.
    totally agree

    did my research and found out the same
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  19. #19
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    I just bought the m665 thinking I'd improve my chain line when set up with a double. Apparently, NOT.

    Dang know it alls \

    Thanks!

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