Page 1 of 2 1 2 LastLast
Results 1 to 25 of 26
  1. #1
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172

    Physical difference between 8 and 9 speed cranksets

    Hi. So as the title says, what are the actual physical differences between 8 and 9 speed cranksets. I'm assuming that the rings may be more narrow? Or more narrowly spaced together? Any other differences?

    The reason i ask is that i want to upgrade to m970 crankset, but my current drivetrain is 8 speed, so i have an 8 speed chain. Would this be an issue at all? I did a search, people have said 'it works', but i would like to know if there is any compromise whatsoever, such as extra wear or shifting problems. I'm particularly worried that an 8 speed chain will wear out the 9 speed crankset faster. Would just like to get some clarification on these queries.

    Thanks.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    1,496
    Whatever differences there are between 8s and 9s cranksets, if any, are insignificant. Depending on the brand there might be minor differences is separation, but things like tooth profile are identical. Any difference in wear would be more dependent on the material of the chainrings, and the condition of the chain.

    The real issue for you, unless you also replace the BB, is the crank offset on the spindle. Unless the suggested spindle length of the new one is similar to what you have, you'll have chainline or chainstay clearence problems.
    fb
    www.chain-L.com

    The key to solving any problem is to understand and address the underlying cause.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jan 2009
    Posts
    148
    i asked about this when i was upgrading my bike and told there is no difference. between 8 and 9 speed the cassattes and chainrings did not get narrower. the space between the cassattes got narrower and the side plates of the chain, but there was no change to the chainrings.

    now on the road bike, there is a difference in the cranks between a 9 and 10, but i'm not sure what it is.

  4. #4
    Mantis, Paramount, Campy
    Reputation: Shayne's Avatar
    Join Date
    Jan 2004
    Posts
    4,363

    If There Is Its Also Imperceptable

    Quote Originally Posted by golfernut78
    now on the road bike, there is a difference in the cranks between a 9 and 10, but i'm not sure what it is.
    My "10spd" drivetrain could care less if I use a current 10spd crank/rings or a crank from the early 80's that has 6spd 'rings.
    *** --- *** --- ***

  5. #5
    Mantis, Paramount, Campy
    Reputation: Shayne's Avatar
    Join Date
    Jan 2004
    Posts
    4,363

    Not Enough To Matter Though

    Quote Originally Posted by golfernut78
    yeah, i don't think there is a difference in the chainrings again, but i think they are spaced differently, where as on the mountain bike crankset they aren't spaced differently between the 7, 8 or 9.
    ...for me.
    I've never dropped a 10spd chain inbetween the chainrings.
    *** --- *** --- ***

  6. #6
    mtbr member
    Reputation:
    Join Date
    Jan 2009
    Posts
    148
    Quote Originally Posted by Shayne
    My "10spd" drivetrain could care less if I use a current 10spd crank/rings or a crank from the early 80's that has 6spd 'rings.
    yeah, i don't think there is a difference in the chainrings again, but i think they are spaced differently, where as on the mountain bike crankset they aren't spaced differently between the 7, 8 or 9.

  7. #7
    mtbr member
    Reputation:
    Join Date
    Oct 2007
    Posts
    2,905
    most 8 speed bikes come with 9spd cranks.

  8. #8
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    I see... How come on the product page, it says:

    Cassette Compatibility: 9-speed
    Chain Compatibility: Super Narrow HG for 9-speed

    It sounds specific. Or does it just mean, its compatible with 9 speed and that chain, as well as being 'backwards compatible'?

  9. #9
    mtbr member
    Reputation:
    Join Date
    Mar 2007
    Posts
    88
    You can also use a Sram chain with it perfectly fine, but it also doesn't say that.

  10. #10
    mtbr member
    Reputation: sanjuro's Avatar
    Join Date
    Sep 2004
    Posts
    2,004
    Chainline is the same.

  11. #11
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Ah ok.

    There's also one bit of concern i have before purchasing the new crankset... I've measured my bottom bracket shell and chain line. BB shell width appears to be 73mm and the chain line appears to be 50mm.

    But the bottom bracket that's on my current crankset doesn't look like the one on the xtr's (or any of the BB i normally see for that matter). The BB on my bike doesn't have a cup that sticks out, rather, it's flush on the left side, and it sticks out like a couple mm on the right side. Will there be any issues with this? It looks like when installing the new BB, it'll make the chain line wider.

    The bike is an 04 gt idrive.
    Attached Images Attached Images

  12. #12
    mtbr member
    Reputation:
    Join Date
    Mar 2009
    Posts
    161
    Shimano FC-M970 crankset is a Hollowtech II type crankset, which uses external bearings (the Hollowtech II bearings are placed outside the bottom bracket shell). You will have to replace the bottom bracket. M970 bearings require a bottom bracket (BB) shell with the width of either 68 mm or 73 mm and with a BSA (English/ISO) thread 1.37" x 24 Threads per inch , Left Handed Thread on the right side of the BB shell and Right Handed Thread on the left side of the BB shell. Chainline is 50 mm.
    Last edited by Seb71; 04-03-2009 at 03:35 AM.

  13. #13
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Thanks for the explanation. The crankset will come with the BB included.

    I guess then the question is really, will a hollowtech ii bottom bracket fit on a 2004 gt idrive? All i know about my existing bottom bracket is that it is a "TruVativ ISIS cartridge" (from bikepedia). My current crankset is a Truvativ Five-D crankset. I measured the BB shell to be 73mm.

    EDIT: I've done some digging. I know nothing of "TruVativ ISIS cartridge", but instead, i looked at the specs of the highest variation of my bike of that year, the idrive 0.0, and it is spec'ed with what i am certain to be the shimano xt m760 crankset, which uses a hollowtech ii bb, no? So if my logic is correct, the xtr crankset should fit on my bike?
    Last edited by peternguyen; 04-06-2009 at 04:58 AM.

  14. #14
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Well, i bought the crankset, there was only one left and it was such an insane deal i could not pass it up. My mechanic says the Hollowtech II BB will fit on my bike.

    There's something else i want to ask now. In the case that this '9 speed' crankset is on an 8 speed drivetrain, would it be more ideal to run an 8 or 9 speed chain?

  15. #15
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    1,496
    Match the chain to the cassette. While a 9s chain will also work, going with the wider chain will pay off with longer chin life, and marginally better shifting, not to mention generally lower cost.
    fb
    www.chain-L.com

    The key to solving any problem is to understand and address the underlying cause.

  16. #16
    mtbr member
    Reputation:
    Join Date
    Jan 2009
    Posts
    148
    Quote Originally Posted by peternguyen
    Well, i bought the crankset, there was only one left and it was such an insane deal i could not pass it up. My mechanic says the Hollowtech II BB will fit on my bike.

    There's something else i want to ask now. In the case that this '9 speed' crankset is on an 8 speed drivetrain, would it be more ideal to run an 8 or 9 speed chain?
    you would base the chain on the cassattes, and not the crankset. if you are running a 8 speed cassatte, go with an 8 speed chain. if you are running a 9 speed cassatte, go with a 9 speed chain. also, a 9 speed chain will work on a 8 speed cassatte.

  17. #17
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Quote Originally Posted by FBinNY
    Match the chain to the cassette. While a 9s chain will also work, going with the wider chain will pay off with longer chin life, and marginally better shifting, not to mention generally lower cost.
    Oh ok. How does wider chain improve shifting?

  18. #18
    mtbr member
    Reputation: cort's Avatar
    Join Date
    Mar 2004
    Posts
    892
    No, you'll be fine

  19. #19
    SoCal Rider
    Reputation:
    Join Date
    Apr 2008
    Posts
    237
    also, not sure if this has been covered already, but you're going to need a new front derailleur. The new 9sp cranksets have a 44T top chainring, and the 8sp Alivo front derailleur you have has a 42T max.

    Let me know how everything works out, as I too am looking for a new 9sp crankset on an 8sp setup.

  20. #20
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Oh s**t, you're right. Never noticed that. You are indeed right, my front derailleur is spec'ed for 42 teeth outer ring. So there is no way i can use that front derailleur? Will i have to buy a new one? Or will keeping the alivio on mean it just won't be optimal?

  21. #21
    SoCal Rider
    Reputation:
    Join Date
    Apr 2008
    Posts
    237
    Not really sure if the Alivo derailleur will work with the 44T, but it's worth a try. Chances are that you'll have to raise the location of the front derailleur a bit, due to the larger chainring size, but doing so will probably effect the shifting of the 2 smaller chainrings.

  22. #22
    mtbr member
    Reputation:
    Join Date
    Nov 2008
    Posts
    1,496
    The difference in radius (height) between a 44t and a 42t is about 4mm, or 1/6". Assuming that there's enough clearance to raise the FD it shouldn't affect performance, but the more serious issue is curvature of the cage.

    It's possible that the larger radius might cause clearance issues at the back of the cage, requiring raising the FD beyond the ideal height over the outer ring. If that becomes an issue, you might want to re-establish clearance by grinding a bit from the rear of the outer cage plate, so it matches the curvature of the 44t ring better.
    fb
    www.chain-L.com

    The key to solving any problem is to understand and address the underlying cause.

  23. #23
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Quote Originally Posted by FBinNY
    The difference in radius (height) between a 44t and a 42t is about 4mm, or 1/6". Assuming that there's enough clearance to raise the FD it shouldn't affect performance, but the more serious issue is curvature of the cage.

    It's possible that the larger radius might cause clearance issues at the back of the cage, requiring raising the FD beyond the ideal height over the outer ring. If that becomes an issue, you might want to re-establish clearance by grinding a bit from the rear of the outer cage plate, so it matches the curvature of the 44t ring better.
    4mm... that sounds like quite a difference considering the cage should be 1-2mm above the big ring.

    Well i have the new crankset installed, put on the front derailleur but didn't have enough time to tune it - it was getting late and the mosquitoes were coming out. So far though the shifting seems to be less than optimal. Maybe i can tweak it a bit more, but i think i will be pursuing in a new front mech very soon.

  24. #24
    SoCal Rider
    Reputation:
    Join Date
    Apr 2008
    Posts
    237
    Let me know if you're able to tune it to work with the new crankset. If not, front derailleurs are super cheap anyway, and you'll shave some weight in the process!

    btw what Shimano crankset did you get?

  25. #25
    mtbr member
    Reputation: peternguyen's Avatar
    Join Date
    Dec 2007
    Posts
    1,172
    Quote Originally Posted by preludedriven
    Let me know if you're able to tune it to work with the new crankset. If not, front derailleurs are super cheap anyway, and you'll shave some weight in the process!

    btw what Shimano crankset did you get?
    Yeah cool, ill tweak it some more tomorow morning and ill let you know how it goes.

    Haha, yeah i suppose (about the weight saving).

    I got the m970.

Page 1 of 2 1 2 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •