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  1. #1
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    Soixante Neuf avec ML8

    I just posted this over on a semi related thread about 69er Mojo's. After reading THC's glowing reports of his ML8 69 build I decided to try the same. After riding 29ers and then returning to 26" bikes I have been missing the big front wheel. A free day on Friday and this is the result. 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, but perhaps the 650b would be the best solution if you like a bigger front wheel as it avoids all the front fork problems. A small spacer could be used with the DUC if needed. Also I have fitted the 08 damper unit on the ML8 (thanks Ethan! ). Its a marked improvement and the rebound damping actually works!
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  2. #2
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    Me Too!

    I have an ML8 with a DUC fork. I installed the 29er conversion kit, a 29er Stans wheel and a Panaracer Rampage 2.3. I am generally pleased with the results. Where I ride, we have lots of baby heads and roots on climbs. The larger wheel/slacker head angle makes it easier to climb over these objects. I tend to climb in a larger gear with this setup. After adding the larger wheel and Speedball seatpost, the bike is up to 30 lbs. When originally built, it was just over 28 lbs. During climbs, the bike is a bit more sensitive to my fore/aft position on the seat. Descents seem more solid. Other than the weight gain, I don't see any significant drawbacks and will continue with this setup.
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  3. #3
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    Well how about that! Are you sure you aint got my bike?!! Have you felt the giro imbalance between the 2 wheels or is that just my imagination?

  4. #4
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    Quote Originally Posted by kidsuma
    Well how about that! Are you sure you aint got my bike?!! Have you felt the giro imbalance between the 2 wheels or is that just my imagination?
    Hard to distinguish between imagination and reality on these very subjective evaluations.

    This is the gyroscopic effect in a bicycle wheel (paraphrased from Wikibpeia): If the wheel is leaned away from the vertical so that the top of the wheel moves to the left, the forward rim of the wheel also turns to the left. Kinda helps with turning. Higher gyroscopic effect would make the bike turn faster when leaned.

    Rotational speed, mass and diameter will impact the gyroscopic effect. SInce the 29er has a larger diameter, it will spin slower than the 26" wheel for a given speed. Thus, I expect the effects would tend to cancel.

    I have found myself going off track periodically, but I have attributed that to higher speeds than I would ordinarily run at, particularly on descent.

  5. #5
    mnt bike laws of physics
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    Yes your right testtech, the Angular momentum would only be more for the 29" wheel because of the additional mass that it has.
    But, because of the addition mass it will be slightly harder to turn - this will only be noticable at higher angular velocities(rotational velocity).

  6. #6
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    End of 69er experiment

    I ran the 29er up front for a couple of months. After a while, I began to suspect that my climbing performance was suffering. At the end, I did a fairly technical 12 mile ride with lots of short, steep, rocky climbs. I have two forks. The following day, I switched forks and did the same ride with a 26" front tire.With the 26" tire, I completed the ride with fewer calories, at higher average speed and cleaned virtually all of the trail obstacles that I failed to navigate repeatedly with the 29" tire in front. Two days later, I rode the same trail again with the 26" tire with similar results.

    My conclusion: The 29" tire sufficiently disturbs the balance of the bike so that significant control is lost on technical climbs. Reduced control and efficiency on climbs more than offsets any gains that may be achieved on descents or ease of clearing small rocks offered by the 29" tire.

    None of this suggests that purpose designed 29er or 69er bikes do not offer benefits. This merely suggests that if you alter well conceived bike geometry, some aspect of performance will likely suffer..

  7. #7
    mnt bike laws of physics
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    You need to use a much lower stem when you add a bigger wheel - or you can use a flat bar if you have a riser. It makes a big difference in climbing. The problem with your fork is that there are not a lot of stem options. Did you try lowering your front end?

    I added a 650b front wheel to my Prophet and Rush. The Prophet needed a lower stem while the Rush did not because the Prophet's HA was 1 degree slacker with the 650b wheel than the Rush and so has more trail.

    You could probably compensate for the excess trail and regain your climbing ability by lowering your grip position while keeping the downhill advantages. My Prophet's downhill perfomance is still much better than before while the tight uphill switchback prowess is spot on with the 650b wheel and lower grips.

    If you cannot dial it in with the 29er, you may give the 650b wheel a try. The current Neo-Moto tire is by far the best front tire I have ever used and there are many more tires on the way if you don't agree. TNC has converted his ML8 to the 650b front/Neo-moto with great success. the longer travel guys are lovin' the fact they are able to keep all of their travel. Personally, I was amazed how much performance gain I got from the conversion. I am racing the setup and have gotten top expert of all the ages the last 2 races(I am 43).

    If you would like any info on geometry, wheel builds or anything else, get back with me.

  8. #8
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    Interesting. I thought TNC converted a Nomad. I have been unable to determine whether a 650B would clear a DUC fork. I believe that it would require 1/2 of the 29er conversion shims.

    When I was riding the 29" wheel, I also missed the plush feel of 6" travel. Of all the changes in the bike, that, at least numerically, was the largest change--the loss of 1.5" travel. The loss of travel is exacerbated by the need to add oil to the air shock to prevent bottoming.

    Before I found the dramatic improvement by simply going back to the original geometry, I planned on trying a 650B. I already have the 650B front tire. Last time I checked, Stans did not have spokes to build a wheel for me. If the 650B could fit without travel reduction, I would try it. So, do you know if anyone has put a 650B on a 6" DUC?

  9. #9
    mnt bike laws of physics
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    Sorry, I must have confused TNC for another. I know I saw a Maverick converted to a 69er somewhere on that forum.

    If you could build your own wheel it would be much better than what stan or anyone else could do. The one I built is the stiffest per weight of anything I have ridden. I haven't yet talked to a wheelbuilder who knows about the physics of a wheel - it is sad. IOW, what it takes to make a wheel that is both light yet laterally stiff. Everyone just goes along using the same size spokes on both sides of a wheel, never questioning, when the stresses on either side are very different.

    You should measure the distance between the top of your tire and the bottom of the fork crown. If there is at least 6-1/2" there will be room as a 650b wheel is 1/2" bigger in radius. That will at least get you an idea.

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