Page 1 of 3 1 2 3 LastLast
Results 1 to 25 of 57
  1. #1
    mtbr member
    Reputation:
    Join Date
    Oct 2005
    Posts
    421

    Frame Flex on Mojo or Mojo SL

    I installed the new annodized upper & lower pivot links to my Mojo.Looks sweeeeet! The one thing that i never noticed untill I installed the new links is the amount of flex between the front & rear triangle? Is this the same on the SL? Basickly all we did was grab the rear wheel while holding the bike & tried twisting back & forth & noticed the amount of flex at the upper link attached to the shock?
    I'm assuming that this was engineered this way? or is there something that I'm missing?

    By the way I ride a Large Mojo. Could this have been the cause of my shifting issues?
    Last edited by scarsellone; 02-19-2008 at 05:51 AM.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Sep 2007
    Posts
    1,140
    uh oh, now you've done it.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Oct 2005
    Posts
    421
    Can someone with more Tech knowledge comment on this issue such as Ibis or DW?
    Did anyone check to see if they had the flex on their Mojo or Mojo SL?

  4. #4
    it's the ride....
    Reputation:
    Join Date
    May 2004
    Posts
    509
    type "flex" in search function of this forum.. and voila..! Yes there are many discussion on this topic.
    Do you feel the difference on the ride before and after links change,,?

  5. #5
    mtbr member
    Reputation:
    Join Date
    Oct 2005
    Posts
    421
    Unfotunetly the weather has not allowed me to try it. I noticed the flex after i changed the links. I'm curious if anyone else has noticed it? Will this become a problem as time passes? i noticed the comparison in the german bike mag, & it mentions flex. I don't question the ride. It ride smooth. I'm more curious if this is designed to take impacts & flex?

  6. #6
    illuminator82
    Reputation:
    Join Date
    Jun 2004
    Posts
    251
    now i am in the minority, but i noticed flex!!! ride was smooth, suspension near perfect, but i could not get over the torsional flex when in the tight stuff. i rode mine back to back with my giant trance for over 3 months and i could discern noticeable flex in the seat tube and top tube areas. basically i felt it when slinging it side to side and it would flex. i felt it would run wide in the turns no matter what i did. rode the same trails with my trance and would rail through the same stuff way faster, period! just my lousy 2cents
    Last edited by brook_63@yahoo.com; 02-20-2008 at 08:43 PM.

  7. #7
    Unpredictable
    Reputation: Ridnparadise's Avatar
    Join Date
    Dec 2007
    Posts
    1,734
    Tighten your shock mounts

  8. #8
    mtbr member
    Reputation: BitterDave's Avatar
    Join Date
    Nov 2007
    Posts
    428
    Quote Originally Posted by brook_63@yahoo.com
    now i am in the minority, but i noticed flex!!!
    You are not alone. Depending on the weave of the CF, there will be some initial "slack" in the frame until the carbon fibers come under tension. It it at this point that the frame will begin to stiffen up. This is probably what contributes to the damped feeling that the Mojo has. I've referred to it as a wigglely feeling. Some like it, some don't, and some don't notice.

    A lot of people have mentioned that the rear triangle is flexy. Some claim it's "controlled flex" and part of the magical damping qualities of carbon fiber. I'm going to disagree with those people. If you study the design of the rear triangle, you will notice that the upper half of the rear triangle is only held together by the rear shock eyelet (the two sides of the upper linkage moves independently of each other). The rear shock is not designed for that type of load. What will happen is that the two sides of the rear triangle will not move as one piece, allowing the rear wheel to pivot/wiggle around. This is in no way considered controlled flex. This may smooth out the ride, but it doesn't add control (hence your wider turns).

    Whether all this flex is good or bad is up to debate since I feel that it's somewhat of a personal preference. If you like the ride/performance of a Lexus, then you will like the Mojo. If you prefer a Ferrari, then the Mojo probably isn't the bike for you. Me, I like BMWs.

  9. #9
    LBS Manager
    Reputation: Johnny Hair Boy's Avatar
    Join Date
    Jul 2004
    Posts
    1,892
    Quote Originally Posted by Ridnparadise
    Tighten your shock mounts
    Ya just tighten it until it breaks and back it off half a turn right.

  10. #10
    mtbr member
    Reputation:
    Join Date
    Sep 2004
    Posts
    642
    complete materials know-nothing here, but i seriously have a hard time believing the carbon fibers tighten with time. that gives me images of the frame actually changing shape to a minute degree. i see clear coat cracking, pivot holes ovalizing or becoming larger, etc. i just don't see it...
    ride fast...take chances...

  11. #11
    mtbr member
    Reputation: BitterDave's Avatar
    Join Date
    Nov 2007
    Posts
    428
    Quote Originally Posted by iridetitus
    complete materials know-nothing here, but i seriously have a hard time believing the carbon fibers tighten with time. that gives me images of the frame actually changing shape to a minute degree. i see clear coat cracking, pivot holes ovalizing or becoming larger, etc. i just don't see it...
    The tension of the carbon fiber doesn't change with time. What I meant to say was that as you start to bend a piece of carbon fiber, the fibers begin to tighten and the rigidity of the piece increases.

    For example, say you take a piece of carbon fiber and gently bend it 1 degree. At this point none of the fibers are under tension, so only the resin is providing the strength. As you bend the piece some more, the fibers come under tension and start to provide additional strength. So for small defections, aluminum can be stiffer than carbon fiber. But as the deflection increases, the carbon fiber can become much stiffer. This lack of stiffness at low deflections is one reason why carbon fiber seems to damp vibrations, but still be structurally stiff.

    The behavior of carbon fiber depends on a lot of things, such as the weave, the resin, and so on. For example, Trek has their OCLV, optimal-compaction, low-void, carbon fiber. What they are basically trying to do is to achieve a tighter weave, so that their frames will still be stiff at low deflections.

    With all things being equal, the Mojo SL should be stiffer than the regular Mojo since Ibis is using a stronger (higher modulus) carbon fiber. Anyone have a chance to ride both side by side?

  12. #12
    Unpredictable
    Reputation: Ridnparadise's Avatar
    Join Date
    Dec 2007
    Posts
    1,734
    Ya just tighten it until it breaks and back it off half a turn right.
    Technique seems to have worked just fine on your brain Johnny HB

  13. #13
    LBS Manager
    Reputation: Johnny Hair Boy's Avatar
    Join Date
    Jul 2004
    Posts
    1,892
    Quote Originally Posted by Ridnparadise
    Ya just tighten it until it breaks and back it off half a turn right.
    Technique seems to have worked just fine on your brain Johnny HB
    Its called sarcasm look it up.

  14. #14
    mtbr member
    Reputation:
    Join Date
    Jan 2005
    Posts
    855
    Can anyone comment on the shape of the Sl anodized links vs the Nickle plated Std Mojo links? I have observed noticable flex in the rear swingarm of the SL setup, and wonder if it is a function of the links or the Sl swingarm itself?
    Last edited by buggymancan; 03-07-2008 at 08:34 PM.

  15. #15
    mtbr member
    Reputation:
    Join Date
    Jan 2005
    Posts
    855
    any thoughts?

  16. #16
    mtbr member
    Reputation:
    Join Date
    Jul 2007
    Posts
    79
    I would send a PM to Hans at Ibis and ask him the question.

    The flex discussions on the forum have been odd in a way. I'm relatively heavy at 185 lbs and there are times when I ride hard considering my grey hair. Flex of my standard Mojo with standard links has not been an issue that has bothered me so far.

    The swingarm design looks like it would flex more than some others that have a brace connecting the two sides beyond the upper link. I don't know how much of that can be mitigated by a very strong composite part.

    The differences in how people perceive flex in their Mojos might be the result of fabrication tolerances or maybe just personal sensitivity.

  17. #17
    Geritol Power
    Reputation: Duzitall's Avatar
    Join Date
    Feb 2004
    Posts
    1,457
    Quote Originally Posted by yo_ca
    The differences in how people perceive flex in their Mojos might be the result of fabrication tolerances or maybe just personal sensitivity.
    Or they could simply be mistaken about what they are feeling. I had a wheel loosen up so fast once that I thought something broke. I haven't ridden a Mojo yet so I don't know if they flex unusually or in a way that I will find unacceptable or not.

  18. #18
    mtbr member
    Reputation:
    Join Date
    Jan 2006
    Posts
    2,501
    From my opinion, a little bit of flex is good cause of dampening and if you crash, you most likely wont damaged the frame badly.

    Too much flex is bad especially for a DW bike. If you went through DW posts bout DW-Link, he has mentioned about the amount of acceptable flex on the DW-Link. I forgot wats the value.
    07 Giant Anthem 2 (Int'l Edition) | omartan.co.cc
    Im a MOJO Fanboy

  19. #19
    mtbr member
    Reputation:
    Join Date
    Jan 2005
    Posts
    855
    Quote Originally Posted by brook_63@yahoo.com
    now i am in the minority, but i noticed flex!!! ride was smooth, suspension near perfect, but i could not get over the torsional flex when in the tight stuff. i rode mine back to back with my giant trance for over 3 months and i could discern noticeable flex in the seat tube and top tube areas. basically i felt it when slinging it side to side and it would flex. i felt it would run wide in the turns no matter what i did. rode the same trails with my trance and would rail through the same stuff way faster, period! just my lousy 2cents
    Brooke, Are you speaking of the SL? and what is your rider weight?

  20. #20
    www.derbyrims.com
    Reputation: derby's Avatar
    Join Date
    Jan 2004
    Posts
    6,788
    Quote Originally Posted by scarsellone
    I installed the new annodized upper & lower pivot links to my Mojo.Looks sweeeeet! The one thing that i never noticed untill I installed the new links is the amount of flex between the front & rear triangle? Is this the same on the SL? Basickly all we did was grab the rear wheel while holding the bike & tried twisting back & forth & noticed the amount of flex at the upper link attached to the shock?
    I'm assuming that this was engineered this way? or is there something that I'm missing?

    By the way I ride a Large Mojo. Could this have been the cause of my shifting issues?
    Go try the same flex tests on other bikes. You'll find the flex of other mountain bikes with similar travel and use is close to the same as the Mojo. With this much travel only some heavier "faux-bar" monopivots such as Kona, Turner, and Trek have stiffer rear wheel flex.

    The fork flex is much more important factor for handling rocks and cornering. The rear wheel pretty much follows the front. If the rear end is stiffer than the fork then handling balance suffers with too much rear sideways chatter or side bounce. It's rare to find forks any stiffer than the flex of the Mojo without going to heavy 20mm axle AM forks. A lighter XC fork with quick release 5mm axle is well balanced for XC/enduro riding, but is a less than completely confidence inspiring on very rocky sections. A 20mm axle AM fork balances the Mojo perfectly for extremely rocky trail handling.

  21. #21
    mtbr member
    Reputation:
    Join Date
    Sep 2007
    Posts
    871
    I totally agree. You need a certain amount of flex. In 1996 Honda went to an
    aluminum frame. The riders were getting thrown off a lot that year. 4 generations later,
    the Honda is a great handling bike, with the addition of more flex in the right places. The Ibis is less flexy than the ellsworth I just sold.
    The Ibis is the most capable xc bike out there IMO. The tires flex a whole lot more anyway.
    Mitch
    Boise

  22. #22
    mtbr member
    Reputation:
    Join Date
    Jan 2005
    Posts
    855
    Again,

    Are you talking about a Std. Mojo or a Mojo Sl? If so, I agree with you on the former, but find the later (Mojo SL) flex, well frankly unacceptable. It seems to stem fron the rear swingarm. Any comments?

  23. #23
    www.derbyrims.com
    Reputation: derby's Avatar
    Join Date
    Jan 2004
    Posts
    6,788
    Quote Originally Posted by buggymancan
    Again,

    Are you talking about a Std. Mojo or a Mojo Sl? If so, I agree with you on the former, but find the later (Mojo SL) flex, well frankly unacceptable. It seems to stem fron the rear swingarm. Any comments?
    I haven't ridden the SL nor have I tried the seat-post/top-of-wheel flex test on the SL. I doubt if there is visible or a tactile difference. The Super-High Modulus CF of the SL is supposed to be stiffer, but geometry is the major factor.

    When you flex test by holding a hand grip and pushing the BB sideways there are very few bikes with less visible and tactile flex.

    Perhaps you tested a bike with some pivot bearing slop or flexy rear wheel.

    To produce a 4.5 pound frame without shock with 5.5 inches of travel, I doubt we will see less flex from any manufacturer for many years.

    There are a few 5.5 inch travel bikes with less flex, but with any of those bikes with less flex you will tradeoff having much added weight, less active or less stable suspension than a dw-link, and noticeable pedaling performance losses (besides other dw-links).

    Ibis had their priorities right in producing the world’s most versatile mountain bike when they designed the Mojo Carbon and SL.

  24. #24
    mtbr member
    Reputation: BitterDave's Avatar
    Join Date
    Nov 2007
    Posts
    428
    This is getting confusing here. I've heard that the SL is stiffer than the regular Mojo, now I'm hearing that it's not. I've been told that flex is good, now I'm hearing that the Mojo has less flex than other bikes??? What gives?

    Unless there is a lot of variation between production frames, the Mojo is one of the more flexy frames that I've come across. Side by side comparison with my Stumpjumper FSR (which I don't consider that stiff) was noticeable enough that I had to get off the Mojo to see if the seat was loose. I also have a 5" travel Enduro that is stiffer than both bikes.

    My hypothesis is that while aluminum/steel has a more linear deflection vs. force curve (the definition of stiffness), carbon fiber has a progressive curve. Small forces will deflect the Mojo frame a fair amount, but once you get crankin' the frame stiffens up. So for those of you who say that the frame is stiff, maybe you aren't noticing the initial (low-force) flex of the frame.

    I guess that instead of saying that the Mojo is flexy, I should say that it has a high degree of defection for the loads that I apply while riding. I notice this both visually (parking lot test) and while riding. Don't get me wrong, I still like the Mojo and may end up purchasing one, but I'm not going to fool myself into thinking that the frame is "stiff".

  25. #25
    mtbr member
    Reputation:
    Join Date
    Sep 2007
    Posts
    871
    my mojo is the standard with a dt.
    Mitch
    Attached Images Attached Images

Page 1 of 3 1 2 3 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
  •