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  1. #1
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    MOJO 69er....and Q for Hans, 29er Mojo?

    I know Derby is trying out the 650, anyone tried a 69 on the Mojo?
    Also a question for Hans and the Ibisinians..... are there any plans for a 29er Mojo? I am riding a Turner Sultan and having owned a Mojo last year reckon a 29er Mojo would go down (and up) very very well. What news say thee?

  2. #2
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    With a Fox 29'er 120mm travel fork it would probably steer OK. It would be crap with out shorter travel and much more fork offset than a 26 fork. I don't have the steering trail calculator link here at work now but you need to do the math to see if the steering trail would be close to the very well optimized stock wheel size steering/handling of the Mojo. Personally, I'd want closer to even travel front travel to the rear on a 5.5 inch FS bike than any 29 wheel front set up allows.

    I'm not totally happy with the 650b with a Fox 32/140 RLC on the front. I need more dry and loose trail time to get a real handling feel. I can't really get a good feel about the handling difference with sloppy and gummy wet and otherwise hardpack trails. It sure rolls easier over rocks and roots and feel great at higher speeds. The slow speed handling feels weird so far, the flexy Fox fork may be part of the problem and the low sidewall profile Pacenti tired 650b wheel is less flexy with nice lower air pressures than a fat tired 26. I'm getting a stiffer PIKE fork soon.

    Could a light-weight 29'er frame be used as a cross frame?

    Edit - added: Here's an easy steering trail calculator. http://www.kreuzotter.de/english/elenk.htm
    First see what your 26 wheel bike's trail is, then for similar handling try to match it closely with a bigger wheel's axle height and axle-to-crown changes to the head angle, plus any fork offset difference.
    Last edited by derby; 03-05-2008 at 09:42 PM.

  3. #3
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    Derby I think your right....it would need a new generation longer offset fork to quicken up the steering. The Mav 36 might be possible too, but I dont know what offset they are building in, probably normal 38/40mm for the 26" wheel. Do post up your 650b ride reports when the trails dry out in the Bay. I still think a 29er Mojo would be major competition for the Lenz,Sultan RIP's etc.

  4. #4
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    things that go 29

    Sorry guys, nothing currently up our collective sleeve...
    H
    Hans
    Ibis Cycles, Inc.

  5. #5
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    Perhaps one day..........


  6. #6
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    Quote Originally Posted by kidsuma
    I just tried the steering trail calculator I edited into my post above and copied here below, comparing the Mojo designed 26 inch wheel and Fox 140mm fork (1.5 inch offset) which makes a steering trail of 3.4 inches, to using a 29 wheel and Fox29/120 specific fork with 2 inch offset (Not sure maybe only Gary Fisher OEM fork is this much offset). The 1.5 inch taller 29 wheel axle height and roughly 1 inch shorter travel net about 1/2 inch higher crown and this would slack the head angle about .5 degree. This 69íer application would make 3.6 inch trail which is a little slower handling and would take some getting used to.

    My 650B wheel in front using the same Fox 140 fork pushed the trail to from stock 3.4 to 3.7 inches and is very noticeably slower and a bit floppy at low speeds. The poorer handling change tradeoff for smoother rolling may not be worth it. Iím going to put my 26 inch wheel on for my next ride to see how that feels again after a couple months with the 650b in front.

    http://www.kreuzotter.de/english/elenk.htm

  7. #7
    mnt bike laws of physics
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    A 29er Mojo would have a very long chainstay as it is already 16.9" with the 26. It is a hard suspension design to fit that big of wheel. Pivot is going to do it, but they are taking radical design measures. Not that the Mojo isn't radical...

    I was thinking about a 26/29 Mojo, but would probably go with the 650b up front instead to get 130mm instead of 100mm of travel and keep the trail at a reasonable length. If you could get a fork with enough offset, the 69er Mojo would be awesome. Unlike Derby, I like less travel up front anyway. It feel more balanced to me, and you get less brake dive. I feel more in control in more varied terrain with less travel up front while keeping the bike at a reasonable weight. What I mean is to get the same stiffness at more travel, you need to make a fork noticable heavier and a heavier front end is not as manueverable or a long flexy front end sucks pretty bad.

    Keep me posted in what you deside. If you can make it work, you may convince me to do it. BTW, I would think 100mm of travel would be the ticket with the 69er conversion, and next year Fox is going to offer their 51mm offset 29er fork for aftermarket sale so I have been told.

  8. #8
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    Upon further review...

    Quote Originally Posted by yogiprophet
    Keep me posted in what you deside. If you can make it work, you may convince me to do it.
    This is a x-post from the 96'er, 650b, etc. forum....

    Well, I tried my 26 inch front wheel yesterday after about 2 months on the 650b. In short, I like the 650b in front better using the same fork. I decided about half way through my familiar single track loop on the 26 that any negative slower steering tradeoffs was not as big as the very noticeable improvement the 650b wheel rolls and absorbs bump hits with the ability to use much lower tire presser without added side rollover or rim wallow with the short sidewall wide round profile Pacenti tire.

    On the flats and uphill The 26 wheel brought back the irregular more choppy front suspension feel compared to the rear smoothness from being more heavily weighted except downhill or while braking. I reduced compression damping some to soften it up but suffered faster brake dive and more wallow. The bigger 650b front wheel balances that bump hit sensation just about perfectly.

    So today I put the 650b back on. Plus I finally bought the stem height spacers needed and lowered my stem the difference in 650b axle height more than the 2.4x26 wheel (1/4 inch) and bumped my seat forward (1/8 inch) to match my many years favorite position over the pedals. And clicked the fork compression up to where I had previously found a nice balance with the rear.

    As soon as I headed down my street on the way to the trail head I could feel my familiar weight again forward on the fork with the bigger wheel removed any floppy slow steering feel I had felt at first. Climbing the switchbacks felt just about same as the previous day on the 26 inch wheel. Just that slight tweak of my fit position remove any weird handling sensations I had previously noticed just swapping to the larger wheel without doing a frame geometry fit adjustment.

    I really think that this slightly bigger front wheel allowing even lower front tire pressures balances a full suspension bike bump it feel and rough trail flow better than same sized wheels front and rear. And Iím realizing that a steering trail difference of up to .2 even .3 inches longer isnít much of a difference as long as the fit is adjusted so rider weight over the wheels remains the same.

  9. #9
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    Soixante Neuf avec le ML8

    To get an idea of what the Mojo might be like 69'd, I decided to build up a ML8 frame into a 69er. I know its a bit off topic but close enough to be of interest I think. Excuse the Maverick photo on this Ibis territory! (I have owned a Mojo) and excuse the mismatching rims and tyres! I just cobbled it together. Ist ride report is this;

    Initial impression was really very good, I immediately liked the bigger wheel up front. The HA is not to slack as the DUC has a low a-c, climbing is still good. The extra roll over of the 29er wheel is a noticable improvement over the 26. Tight singletrack was fine and fast rocky downhills were a breeze, super stable with the big wheel and all that travel up back. Also I got into a fast slide on leaves over greasy mud and it felt easier to control the slide with the big/small wheel combo. I could also notice the increased zippy acceleration compared to my 29er Sultan. On a negative there were 2 things.....
    I could feel the imbalance of gyroscopic force between the 2 wheels....the front being more stable than the back. Its a strange sensation, not bad but just very different from anything I have ever felt. I could get used to it though.
    Secondly the imbalance of travel, 120mm front to 165mm rear. Even running more sag at the back it showed up the lack of travel at the front. I reckon there could be a great bike here but it needs a fork made to measure, with as low an a-c as possible with maximum travel.
    So great fun to do and get the feel of the 69 beast. If I had a Mojo frame and a WB 135 29er fork lying around I would give it a go but perhaps the 650b is the best compromise.
    Attached Images Attached Images

  10. #10
    mnt bike laws of physics
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    Quote Originally Posted by kidsuma
    I could feel the imbalance of gyroscopic force between the 2 wheels....the front being more stable than the back. Its a strange sensation, not bad but just very different from anything I have ever felt. I could get used to it though.
    .
    I have heard many talk about the "gyroscopic force or effect" (what is called angular momentum -L) of the 29er wheel compared to the 26er.

    We need to remember that the 26er is rolling faster than the 29er at a rate that is linearly dependent upon the radius and angular momentum is linearly dependent on (1)angular velocity and (2)mass times distance from the center of rotation. (unlike the moment of inertia which deals with acceleration. This depends on the mass times the distance squared which is why 29er acceleration should be noticably slower). What this means is that the difference in L is only attributed to the difference in mass of the 2 wheel/tire systems. This should not be as noticable as the acceleration difference.

    Since the front wheel has much less trail than the rear wheel, I would think that a bigger wheel up front(of a full suspension bike anyway) would only have advantages unless the difference in travel is something that disturbs.

  11. #11
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    Oh cool a 29er Mojo would be nice, but it looks like that is a loooong ways off, guess I will getting the Moots Mooto-XZ first, full 29er sure is sweet in rocky stuff, just floats over stuff that 26er get sucked into

  12. #12
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    Quote Originally Posted by yogiprophet
    I have heard many talk about the "gyroscopic force or effect" (what is called angular momentum -L) of the 29er wheel compared to the 26er.

    We need to remember that the 26er is rolling faster than the 29er at a rate that is linearly dependent upon the radius and angular momentum is linearly dependent on (1)angular velocity and (2)mass times distance from the center of rotation. (unlike the moment of inertia which deals with acceleration. This depends on the mass times the distance squared which is why 29er acceleration should be noticably slower). What this means is that the difference in L is only attributed to the difference in mass of the 2 wheel/tire systems. This should not be as noticable as the acceleration difference.

    Since the front wheel has much less trail than the rear wheel, I would think that a bigger wheel up front(of a full suspension bike anyway) would only have advantages unless the difference in travel is something that disturbs.
    Your comment on front to rear wheel trail is interesting. Does rear wheel trail have any effect on cornering? The rear doesn't steer other than drifting. There is a wheelbase change when compressing in corners which would be determined by front and rear path slope change during travel. (It gives me something to think about more.)

    It's still difficult find a fork to put a bigger wheel on a bike without increasing trail, resulting in a slower steering feel. For some of us a little slower steering feels good, it produces a smoother bump hit angle (even if using a wheel the same size but increasing crown height), but it's a little "heavier" and floppier at low speeds. But most XC racer types like shorter trail and quick steering (many use long slow steering stems for more stretched out climber and aero fit).

  13. #13
    Too Much Fun
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    Quote Originally Posted by hanssc
    Sorry guys, nothing currently up our collective sleeve...
    H
    ...Thats fine Hans, just finish up on that new Ibis Cross bike and its all good.

    - -benja- -

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