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  1. #1
    mtbr member
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    New question here. 9-spd cassette on 8-speed hub...

    i'm 90% sure the answer is no, but wanted to check here:

    i'm thinking i can't run a 9spd cassette on an XTR M950 hub (8spd), right? freehub not long enough to accept the wider cogset?

    thanks in advance.

  2. #2
    Nouveau Retrogrouch SuperModerator
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    You are 90% wrong. They are the same width--freehub body and cassette..
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  3. #3
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    really?! well that's good news i suppose...

    so why are some hubs designated as 8 spd compatible vs. 9spd compatible?

    thanks shiggy.

  4. #4
    JmZ
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    Quote Originally Posted by gotdirt
    really?! well that's good news i suppose...

    so why are some hubs designated as 8 spd compatible vs. 9spd compatible?

    thanks shiggy.
    Marketing.

    Just like some companies front chain rings were marketed as 9 speed vs 8 speed when their rings were the same.

    I've ridden Nuke Proof (before 9 speed came out) as 9 speed, so I'm positive it can be done.

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  5. #5
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    8 speed and 9 speed have the same width freehub, it's 7 speed that's narrower. The spacing between the gears of 8 speed and 9 speed is different. You have to use a spacer behind a 7spd cassette to fit it on a 8/9 speed freehub. There is a 8 speed cassette for a 7 speed freehub body. The lockring is replaced by the eigth cog.

  6. #6
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    okay, starting to make sense...

    so then i guess the difference between 8/9 spd componentry is primarily width? i.e. chainrings and chains... that is, if the cassette fits in the same space, then each cog is slightly narrower and the shift points are slightly closer together?

    thanks for the replies.

  7. #7
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    Actually, the cogs are the same width, but the spacing is closer. That's why a 9 speed chain will work fine with an 8 speed cassette. Its also why 9 speed chains are WAY less durable. Because the outside width got narrower while the inside width stayed the same. So in essence, the plates on the chain got thinner (and weaker).

  8. #8
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    Actually, I'm pretty sure that it's the rollers that are narrower, not the links themselves.

  9. #9
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    Well...8 speed SRAM and Shimano cassettes use 1.8mm thick gears and 3.0mm spacing. 9 speed SRAM cassettes use the same 1.8mm thick gear with 2.54mm spacing while Shimano goes a whole 0.02mm thinner to a 1.78mm thick gear and 2.56mm spacing.

    http://www.sheldonbrown.com/k7.html

    So the rollers really can't be any narrower or they wouldn't fit on the gears. The only thing they could make narrower is the plates

  10. #10
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by XSL_WiLL
    ... There is a 8 speed cassette for a 7 speed freehub body. The lockring is replaced by the eigth cog.
    No, there is not. On a 7-speed hub/cassette the small cog is also the lockring and is threaded onto the outside of the freehub body. There is a way to hack 8 cogs on a 7-spd FH though.

    And it is mainly side plate and pin (not roller) thickness that is the difference between 8 and 9 speed chains. Any inside width change (if any) is very minor.
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  11. #11
    ravingbikefiend
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    I'm not a fan of 8 and 9 speed drives as there are simply too many gears crammed into too small a space. Wheel dish and chain deflection become major issues and these lead to a higher rate of wear on components which is good for component makers as parts need more frequent replacement.

    Marketting plays a huge role in all of this because if 21 speeds was good then 24 had to be better and 27 has to be the best... yuh huh.

    My road bikes run 1 to 18 speeds, my mountain bikes run 1 to 6 speeds (with a 2 by 3 setup), and my cross bike just went from 24 to 10 speeds. I dropped the granny and 3 of the 8 gears in the rear.

    I still have the same gear range on my cross bike as folks running 24 and 27 speed drives but a number of those middle gears have been removed to narrow the cogs width which improves chainline, reduces wear, and makes for a better running drivetrain.

    I liked running my HT as a 1 by 7 (it is now an SS) as although there was some deflection at the outer gears it was far less than what one sees in an 8 or 9 speed setup. This deflection is enough to warrant the addition of a chain guide on 1 by 9 setups to keep the chain from jumping off the chainrings but is something a 1 by 7 probably won't need.

    A singlespeed or bike with an internal gear hub will enjoy the longest chain life and experience the least wear on the rings and cog since the chainline is always straight which also increases performance.

    This is one of the reasons ss riders can run higher gearing and still enjoy great performance... it's all about driveline efficiency.

    I always wonder how the rocket scientists at Shimano and SRAM can justify 9 speed drives as being superior because the phyics and real world testing doesn't support this.

    A 5 speed freehub and cassette would be the shizzle but until then I'll keep modifying what is available.
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