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  1. #1
    FM
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    26" AM hardtail conversion- geometry ?

    Wondering about throwing 650b wheels on my 26" Curtlo AM hardtail. The bike is sweet but I haven't ridden it much since getting into 29'ers... I've since sold my yelli screamy so thinking about a refresh on the curtlo.

    The frame has paragon sliding drop-outs, so I'm pretty sure the back would take a 650b just by adjusting the drops back 3/4". It wouldn't kill me to replace the fork if needed (currently a 150mm talas 32).

    Geometry is the big question, especially BB height. Currently with 26" wheels the BB sits at 12.5" with the fork at 120mm (69d head angle), or 12.75 with the fork at 150mm (67.5" head angle).

    Thinking bigger wheels generally play well with shorter forks, steeper angles and skinnier tires, so reducing fork travel or running a skinnier rear (i.e. 2.2) might not be bad compromises, and both would help drop the BB. Also considering just a 27.5" front wheel as an option.

    IMG_3595

    Any thoughts? My frame geometry is pretty similar to a transition transam or chromag samurai, so any thoughts on running those bikes with 650b would be helpful.

  2. #2
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    I converted a Santacruz Chameleon into 27.5", but as you said I did put in a 120 mm fork, which in fact did helped with the geometry. As of BB height, since the Chameleon has an eccentric bb then I put it at 6 o'clock reducing the bb height to about 12.6-7". I do like the way it handles, and no complaints in responsiveness.

  3. #3
    FM
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    Thanks 40'er. BB height is really my only concern at this point. I think 27.5 wheels would put my BB over 13", and I'm not much of a high BB fan. On the other hand, I could always run just the 27.5" in front, which would basically maintain the current geometry if I drop the fork 20mm.

  4. #4
    NedwannaB
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    Looks like you're running a good size tire in back already. Using some measurements from my xc hardtails that I run the 650's on, you'll need about 14.25" minimum from cntr qr axle to back of seat/chain stay bridges. My braces are about 1.75" wide and then the stays roll out from there. I can run 2.2 Wolverines without any side rub. As far as bb ht, that depends on the tires you have on now. Figure basically a half inch more from 2.1-2.2 26" tires. Mine being Wolv-Wolv's. Nevegals-Nevegals. YRMV....
    Wait,who did he tell you that?....

  5. #5
    FM
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    Thats encouraging. 1/2" of added BB height I can deal with... 3/4" or more would be pushing it.

    As for tire clearance, there's plenty of "depth", but the width may be a limiting factor. 26x2.2 is about as big as I can go. The tire shown rubbed just a little bit. But I have 3/4" of unused chainstay adjustment so I think I can just move the wheel back to maintain the same clearance.

    Thanks for the info. Got some feelers out to see if there's a wheelset I can borrow. if not, might just pony up to try it.

  6. #6
    NedwannaB
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    Quote Originally Posted by FM View Post
    Thats encouraging. 1/2" of added BB height I can deal with... 3/4" or more would be pushing it.

    As for tire clearance, there's plenty of "depth", but the width may be a limiting factor. 26x2.2 is about as big as I can go. The tire shown rubbed just a little bit. But I have 3/4" of unused chainstay adjustment so I think I can just move the wheel back to maintain the same clearance.

    Thanks for the info. Got some feelers out to see if there's a wheelset I can borrow. if not, might just pony up to try it.
    If you have sliders you should be good to go. Is that tire in back a Spec Purgatory 2.2? If so they run pretty big.
    Wait,who did he tell you that?....

  7. #7
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    Keep us posted on this. You should have no big issues other than the increased bottom bracket height (but to you that could be a big issue since I think you prefer lower/low-ish bottom bracket heights right?).

  8. #8
    FM
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    Thanks all.
    Tire in back is a Bontrager Big Earl 26x2.3 of some sort. Barely fit with the chainstays @ 16.5", It's since been replaced.
    I do prefer lower BB's. I don't think I'd care for the ride if the BB goes over 13", but hard to say. Ideally I'll be able to borrow a pair of wheels for testing before investing.

    I will post back- I'll probably do this at some point this season!
    Last edited by FM; 11-19-2012 at 08:25 AM.

  9. #9
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    Any updates on this experiment, FM?

  10. #10
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    I think he sold the frame

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