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Thread: Mojo chainline.

  1. #1
    It's the axle
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    Mojo chainline.

    I notice the chainline on my Mojo is way off from what I expected. I'm wondering, before I consider changing it, if there is a reason for this.

    I've got the medium frame. M960 XTR cranks and bottom bracket. Industry Nine wheelset. I have the XTR 9speed cluster. I'm using two stock spacers on the drive side.

    I've measured 51mm from the center of the frame to the middle chainring.
    I measure 22.5mm from the inside dropout to the middle cog.

    With a 135mm axle, that yields a 45mm chainline for the cassette.

    51mm and 45mm seem pretty far off.

    If anything, I'd like the chainline to be off in the other direction. So this seems way way off.

    Is this the way it should be? I'm asking this here rather than the drivetrain forum, since Ibis eyes are here.

    Thanks.

  2. #2
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    I thought I read that the correct spacing on a Mojo with XTR was either 0 or 1 spacer on the drive side, but I don't know where I saw that........???

    Wouldn't that bring the measurements more in line? The back can't change, so you have to change the line in the front to bring them closer.

    Double check your method and accuracy too. Here is a good brief description of calculating chainline: http://miketechinfo.com/new-tech-chains.htm

    P.S. I get measurements of 47.5mm for the rear and 49-50 on the front (but I use FSA and ISIS drive up front).
    Last edited by noshortcuts; 04-30-2007 at 03:27 PM.

    "I must not be crazy because I'm seriously questioning my sanity"

  3. #3
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    Hello Gregg,
    Tom from Ibis posting. The Shimano specification for the BB center-to-middle chainring measurement on a M960 crankset is: 47.9 mm (48.3 on an M970). The Mojo uses a 68mm BB shell. So the correct set-up is 2 spacers on the drive side, 1 on the non-drive side.

    The Mojo was designed in accordance with the Shimano spec, and the BB shell is a molded in part. So there's not a lot of opportunity for variance. I would double check your measurement there.

    Also, I would double check your rear measurement too. The method described on the miketechinfo.com site is a good way to go. It should be in the 40 to 41 mm range measuring from the inside of the cassette to the inside face of the dropout - resulting in a 47.5 mm chainline measurement.

    I just measured a bike in the office with a M960 to double check that too, and it was on the money.

  4. #4
    It's the axle
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    Tom,

    I didn't mean to take you away from whatever you were doing. And to be honest, I have no issue with shifting at all. I was just done with the bike and decided to check the one thing I haven't checked.

    I've measured four times, and in different ways. I keep coming up with the same numbers. Except that the miketech way of measuring gives a slightly bigger number due to the way they measure. They include the gap between the freewheel and the dropout. But it gets cut in half due to averaging. So it's off by a little under a millimeter. And I suppose that's good enough. Beside, my crank arms are both the same distance from the centerline of the bike. And that's probably more important than having the chainline exactly where I'd like it to be.

    I realize the bike is designed to certain standards. I guess I should be riding and not measuring.

  5. #5
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    Chain gang

    Hi Gregg,

    I'm sorry if my response sounded short, or defensive. It was not my intent at all. It was just late in the day and I wanted to get you as much information as I could as quickly as I could. Sorry if it didn't come out sounding that way.

    Anyway, the point is that your bike is working properly and that you are enjoying it. That's all that matters.

    Let me know if there's anything else we can help you with: info@ibiscycles.com

  6. #6
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    ???spacer equals 2.5mm spacer???

  7. #7
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    Yes, the stock spacers are 2.5 mm in thickness

  8. #8
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    New question here. Chain line issue with SX

    Quote Originally Posted by Tall Tom
    Hello Gregg,
    Tom from Ibis posting. The Shimano specification for the BB center-to-middle chainring measurement on a M960 crankset is: 47.9 mm (48.3 on an M970). The Mojo uses a 68mm BB shell. So the correct set-up is 2 spacers on the drive side, 1 on the non-drive side.

    The Mojo was designed in accordance with the Shimano spec, and the BB shell is a molded in part. So there's not a lot of opportunity for variance. I would double check your measurement there.

    Also, I would double check your rear measurement too. The method described on the miketechinfo.com site is a good way to go. It should be in the 40 to 41 mm range measuring from the inside of the cassette to the inside face of the dropout - resulting in a 47.5 mm chainline measurement.

    I just measured a bike in the office with a M960 to double check that too, and it was on the money.
    Hi

    I've just got my mojo & noticed a similar issue with mine. A straight line on my middle ring goes to the 6 or 7 the smallest on the rear, and not the 5th as I'd like. I guess I'm really noticing the different to my Giant Reign which seemed to have a better line. I usually climb in 3 on the rear & the middle ring, so find & hear quite a bit if unusual noise due to the line.

    I've got a medium frame (SX spec) running an XT BB & cranks. Following the instructions from the link above, my measurements come out like this:
    Rear: 47.5mm ([135-40]/2)
    Inside rear drop-put to middle ring on cassette is 24mm (approx).
    Front: 51mm from bb centre to inside of middle ring. Note that the ring is about 4-5mm thick dependin on where it is in it's rotation. So I guess I should add an extra 2mm to this giving 53mm.
    BB shell is 68mm, BB width (outer edges) is 95mm.
    There are 2 spaces on the drive side, and 1 on the non-drive side. These appear to be about 2.5m each.
    So it seems to me that my BB is to wide, or I need to move/remove spacers.

    Any thoughts?

    Thanks in advance.

  9. #9
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    More chain line

    Quote Originally Posted by jacko69
    Hi

    I've just got my mojo & noticed a similar issue with mine. A straight line on my middle ring goes to the 6 or 7 the smallest on the rear, and not the 5th as I'd like. I guess I'm really noticing the different to my Giant Reign which seemed to have a better line. I usually climb in 3 on the rear & the middle ring, so find & hear quite a bit if unusual noise due to the line.

    I've got a medium frame (SX spec) running an XT BB & cranks. Following the instructions from the link above, my measurements come out like this:
    Rear: 47.5mm ([135-40]/2)
    Inside rear drop-put to middle ring on cassette is 24mm (approx).
    Front: 51mm from bb centre to inside of middle ring. Note that the ring is about 4-5mm thick dependin on where it is in it's rotation. So I guess I should add an extra 2mm to this giving 53mm.
    BB shell is 68mm, BB width (outer edges) is 95mm.
    There are 2 spaces on the drive side, and 1 on the non-drive side. These appear to be about 2.5m each.
    So it seems to me that my BB is to wide, or I need to move/remove spacers.

    Any thoughts?

    Thanks in advance.
    Hello Jacko69,

    The Shimano front chain line specification for the FC-M760 crankset is 50 mm. Note, Shimano only offers chain line specifications for the front. There is an assumption that if the cassette to inner drop out face gap measurement is within spec, then the rear chainline will be as well.

    In regard to the rear chainline, I didn't have a set of the Crossride wheels with the SRAM cassette around to double check, so we'll assume that the 47.5 rear chainline you measured was correct - this is what I measured on a set of Easton XC-1 wheels with the SRAM casstte.

    To double check the front, I installed a FC-M760 crankset on a Mojo with two spacers on the drive side and one on the non-drive side (note: when used with a 68 mm BB shell you must use 3 spacers in some combination). I measured the front chainline from the center of the BB shell to the inner face of the middle chainring (this is the Shimano designated method) to be 50 mm or just slightly less. So this would be right on the mark.

    In regard to your specific situation, as I mentioned above, the correct front chainline measurement - based on the information you've provided - would be 51 mm, not 53. Assuming that you measured that correctly - which is not easy given the uneven surface of the chainring - I'd say that you're pretty close to the nominal chainline specification. Also, it sounds like the BB shell is within tolerance. So my question would be - are you having any shifting problems? If not, I would recommend not doing anything. I do not recommend moving the spacers around. Mojo owners who have set their bikes up with 1 spacer on the drive side have experienced problems with shifting and chainsuck. If you are having shifting problems, it is hard for me to diagnose the problem and offer a solution based upon the information provided. I doubt that the shifting problems would be a result of the chainline. Your set up is minimally beyond the specifications and drivetrains are generally capable of handling much sloppier tolerances. I could only suggest visiting your LBS.

    There is also the possibility that the sound your hearing is not the result of the chain line, but actually a problem with the chainrings. Shimano had a design issue on some of their '06 XT cranks. Check the date code stamped on the inside of the driveside crank arm around the pedal spindle hole. It should be a two letter code like EL or FI or something. The first letter stands for the year, E = 2006, and the second letter is the month. Anything earlier than EI (September, 2006) may be a problem. And you should contact Shimano directly about getting replacement chainrings.

    I'm sorry not I'm not able to offer you a cut and dried solution. But feel free to contact us directly if there is anything else we can do for you.

  10. #10
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    Quote Originally Posted by Tall Tom
    Hello Jacko69,

    The Shimano front chain line specification for the FC-M760 crankset is 50 mm. Note, Shimano only offers chain line specifications for the front. There is an assumption that if the cassette to inner drop out face gap measurement is within spec, then the rear chainline will be as well.

    In regard to the rear chainline, I didn't have a set of the Crossride wheels with the SRAM cassette around to double check, so we'll assume that the 47.5 rear chainline you measured was correct - this is what I measured on a set of Easton XC-1 wheels with the SRAM casstte.

    To double check the front, I installed a FC-M760 crankset on a Mojo with two spacers on the drive side and one on the non-drive side (note: when used with a 68 mm BB shell you must use 3 spacers in some combination). I measured the front chainline from the center of the BB shell to the inner face of the middle chainring (this is the Shimano designated method) to be 50 mm or just slightly less. So this would be right on the mark.

    In regard to your specific situation, as I mentioned above, the correct front chainline measurement - based on the information you've provided - would be 51 mm, not 53. Assuming that you measured that correctly - which is not easy given the uneven surface of the chainring - I'd say that you're pretty close to the nominal chainline specification. Also, it sounds like the BB shell is within tolerance. So my question would be - are you having any shifting problems? If not, I would recommend not doing anything. I do not recommend moving the spacers around. Mojo owners who have set their bikes up with 1 spacer on the drive side have experienced problems with shifting and chainsuck. If you are having shifting problems, it is hard for me to diagnose the problem and offer a solution based upon the information provided. I doubt that the shifting problems would be a result of the chainline. Your set up is minimally beyond the specifications and drivetrains are generally capable of handling much sloppier tolerances. I could only suggest visiting your LBS.

    There is also the possibility that the sound your hearing is not the result of the chain line, but actually a problem with the chainrings. Shimano had a design issue on some of their '06 XT cranks. Check the date code stamped on the inside of the driveside crank arm around the pedal spindle hole. It should be a two letter code like EL or FI or something. The first letter stands for the year, E = 2006, and the second letter is the month. Anything earlier than EI (September, 2006) may be a problem. And you should contact Shimano directly about getting replacement chainrings.

    I'm sorry not I'm not able to offer you a cut and dried solution. But feel free to contact us directly if there is anything else we can do for you.
    Thanks for the reply "Tall Tom".

    It sounds like I'm pretty much set up correctly then. My measurement from the BB centre to the inner surface of the middle CR was 51mm - could be 50mm if I'd taken a fatter section of the ring.
    I don't have any shifting issues, just a little noise when using the 3rd largest rear-cog with the middle CR.
    Oh, and I'm running an XT cassette with Mavic xm819 & XT hubs giving the 47.5mm rear chain line. XT cranks are marked EL.

    Cheers.
    Last edited by jacko69; 06-18-2007 at 03:32 PM.

  11. #11
    Wzl
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    Good information here. I posted on another thread and was directed here but this is my question. My M760 Crank is set up with a 22-36 chainring combination and there are two spacers on the drive side. I often climb in the middle ring using the 30 or 34 tooth cogs. On other bikes this doesn't seem to be much of a problem. On my new Mojo however, this causes a bit too much noise to the point that it sounds like a very dirty drive drain. Others have told me that I just shouldn't be this far crossed up but I say this works on my other bikes and I know plenty of other riders who do the same thing.

    I could take out one spacer from the drive side to see the effect. I read here that this could cause shifting problems and potential chain suck. Well, during my first ride I suffered two episodes of chain suck dropping from the middle ring to the granny gear so obviously I already have a problem. Then I read here that there was potentially a problem with XT cranks produced before September of 2006. Well, my middle ring is actually an LX ring but it says FC on it so I believe it should be OK.

    Does everyone else just suffer through this problem or does everyone else really honestly not run their top 3 cogs in their middle rings?

  12. #12
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    Typically don't go into the 34 (1st) while in middle ring. But I do use the 30 and the 28 (2nd 3rd). I have no problems getting to any of them (even the 34) on the Mojo. I am using a new M760 crank with a M960 XTR front derailleur with an X.O. rear. SRAM PG990 chain.

    Is the noise your hearing the chain rubbing against the front derailleur? If so, you can easily adjust the cable tension looser which will allow the derailleur to move in to the frame side just a little. This should stop the rubbing. If this causes the derailleur to not shift to the big ring properly, or drop off the small ring when you shift, you can adjust the stops a little and reset your cable tension again.

    Did you install the front derailleur yourself? if so, It can be a bit tricky to get it in the right spot vertically. Also, you want to make sure that it is square with the chainrings. Not towed in or out. There are plenty of posts about setting this properly. I'm sure you can find some into.

    I'm guessing that if you re-adjust your front der., you won't have any chain dropping issues. If you still do, I'd be curious of the length of your chain and the read derailleur that you are using. Also, how long it's been in service.

    Good luck!

    --MXFanatic

  13. #13
    Wzl
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    Brand new bike. Rode it on Sunday, Tuesday, and Wednesday.

    Chain suck issue I will attribut to overly sticky lube. Cleaning and relubing with a dry lube appears to have fixed the suckage issue.

    Front derailleur is aligned correctly though it may be a tad high. That's the first thing I looked at to see where all the racket was coming from. Then I looked at the chainline and saw how crossed up it was.

    After reading some of these posts about people not using the full range of gears with their middle ring I was a bit dishelved. I called one of my riding buddies who is a professional mechanic, frame builder, commercial welder, and a few other things. I asked his opinion and he said it shouldn't be that bad and that he and everyone else we know use the middle ring and biggest cogs all the time. This leads me to believe this chainline issue can be fixed.

    Saying you can't use the top 1 or 2 cogs on a cassette while in the middle ring is akin to saying you can't use the bottom two. So then what do you say to all those people who are running 2x9 drive trains?

    I tried removing one of the drive side spacers this morning but then realized that the adjustment screws on the front derailleur are a pain in the ass to get to on this frame. So I haven't had a chance to try this mod out just yet but I will get it dialed by the weekend.

    I am running a medium cage XO rear derailleur with an 11-34 cassette and a PC991 chain. The front derailleur is an XT. I haven't counted the links but the length is correct.

  14. #14
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    Quote Originally Posted by Wzl
    Saying you can't use the top 1 or 2 cogs on a cassette while in the middle ring is akin to saying you can't use the bottom two. So then what do you say to all those people who are running 2x9 drive trains?
    I am running a medium cage XO rear derailleur with an 11-34 cassette and a PC991 chain. The front derailleur is an XT. I haven't counted the links but the length is correct.
    I agree with you about that. It should work OK in the mid ring x 34t and you should not have to avoid that combination.

    The frames are usually super straight with an alignment variance of about 1mm or less from the bb to the rear drops.

    Medium cage XO... Hmm that sounds familiar, as in a recent post recommending long cage instead...Legendary Customer Service!

    Feel free to email or call us if you like, maybe we can help.
    Hans from Ibis.

  15. #15
    Wzl
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    Quote Originally Posted by hanssc
    I agree with you about that. It should work OK in the mid ring x 34t and you should not have to avoid that combination.

    The frames are usually super straight with an alignment variance of about 1mm or less from the bb to the rear drops.

    Medium cage XO... Hmm that sounds familiar, as in a recent post recommending long cage instead...Legendary Customer Service!

    Feel free to email or call us if you like, maybe we can help.
    Hans from Ibis.
    I just may call you tomorrow so that I can understand this but for now, as was asked in the post you linked to, can someone please explain why it must be a long cage?

    I admit I was warned about the medium cage but I was told it was due to chain slap, not an overly crossed up drivetrain.

    For now, I have a long cage on my Ventana El Saltamontes so I'll swap it out and see what the effect is. If it fixes the problem then I guess I'll be giving Stevie down at Fat Tire Cycles a call to let him know that you guys will be sending him a new derailleur(????)

  16. #16
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    Quote Originally Posted by Wzl
    I just may call you tomorrow so that I can understand this but for now, as was asked in the post you linked to, can someone please explain why it must be a long cage?

    I admit I was warned about the medium cage but I was told it was due to chain slap, not an overly crossed up drivetrain.

    For now, I have a long cage on my Ventana El Saltamontes so I'll swap it out and see what the effect is. If it fixes the problem then I guess I'll be giving Stevie down at Fat Tire Cycles a call to let him know that you guys will be sending him a new derailleur(????)
    We supply the long cage in our SX kit and it seems to work fine with the Shimano chain and XT cranks:
    http://www.ibiscycles.com/mountain/parts_pick/

    Whatever the case, I'm sure we can resolve it

    Maybe I'll learn something in the process....

    H

  17. #17
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    Quote Originally Posted by Wzl
    I admit I was warned about the medium cage .....

    For now, I have a long cage on my Ventana El Saltamontes so I'll swap it out and see what the effect is. If it fixes the problem then I guess I'll be giving Stevie down at Fat Tire Cycles a call to let him know that you guys will be sending him a new derailleur(????)
    You are saying you were warned about possibly using a medium cage and yet you believe the bike manufacturer is responsible for giving you a free long cage?

    lol - i love this country at times.
    Last edited by zzsean; 07-26-2007 at 09:58 PM.

  18. #18
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    Quote Originally Posted by Wzl
    I admit I was warned about the medium cage but I was told it was due to chain slap, not an overly crossed up drivetrain.
    How many chainrings are you using on your crankset? The length of a cage will definitely have an impact as far as usable gearing combinations are concerned.

    Here's a great post from Speedhub Nate which describes the differences and when you should be using a long/medium/short :
    When to use a Long Cage vs Short Cage Derailleur?

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