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  1. #1
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    Optimum Axle to Crown for 69er conversion

    I'd like to convert my Kona Titanium Singlespeed 26er with front suspension into a full rigid 69er. Currently looking at a White Bros. Carbon rigid fork w/ 445mm axle to crown measurement. Don't want a fork so tall it slows the handling but I'm uncertain as to what measurements I should be looking for. I've seen 26" rigid forks from 409mm to 470mm.

    (frame was designed to use an 80mm travel fork)
    Last edited by Spastook; 01-24-2012 at 07:21 PM.

  2. #2
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    "Optimum" depends on the a-c length your frame was designed for... I used this article as a guide http://www.dirtragmag.com/printrag/m...our-own-2926er in dirt rag to convert a bike a while back.

    I've since robbed the bike of parts for another build, but i did really like the ride.

    Good luck!

    PS- you might get more advice in the 69er section...

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  3. #3
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    I just put a 26" disc only Salsa Cro Moto fork on my 26" Kona Explosif frame and I'd bet I could fit a regular 29" tire/wheel combo in it although I haven't tried just yet. I do have 29" wheels on it actually with Bontrager 32mm tires front and rear and there's a ridiculous amount of clearance above the current "road" tire in the front.

    This one

    Salsa Cycles | Components

  4. #4
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    Hey man, I have a 2008 Trek 69er frame in Rootbeer, brand new waiting to get built up. I don't have the cash to build it so if you want a true "69er" let me know! Haha
    My motorcycle runs on infant blood

  5. #5
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    Quote Originally Posted by Spastook View Post
    I'd like to convert my Kona Titanium Singlespeed 26er with front suspension into a full rigid 69er. Currently looking at a White Bros. Carbon rigid fork w/ 445mm axle to crown measurement. Don't want a fork so tall it slows the handling but I'm uncertain as to what measurements I should be looking for. I've seen 26" rigid forks from 409mm to 470mm.

    (frame was designed to use an 80mm travel fork)
    You could use something like a Salsa Cromoto 425mm a/c, that will still give you more than enough tyre clearance for something like a 2.35 Rampage. However, I think that the 38mm offset of that fork (and most other forks intended for 26" wheels) isn't sufficient for optimum handling with a 29" wheel, so you end up with too much trail resulting in that "floppy" feel at low speeds.
    If you can live with 445mm a/c then the best fork you could get (IMHO) is the fork that Singular Cycles use on the Hummingbird 69er (and also the Gryphon, I believe).
    This has 55mm offset which works far better with the bigger wheel, as it gets the trail back down to a sensible amount and, as a bonus, gives fewer problems with toe overlap too.
    Nicest steel fork that I've ever used.

  6. #6
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    [QUOTE=jten9;8940038]"Optimum" depends on the a-c length your frame was designed for... I used this article as a guide Making Your Own 29/26er | Dirt Rag Magazine in dirt rag to convert a bike a while back.


    Thanks, I read this article from Dirtrag and based on their formula it looks like a 425mm axle to crown measurement would work best for me. The White Bros. fork I've looked at is available in that length.

  7. #7
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    I've used a Surly 1x1 in the past, its only 413 ac and has a good 45mm offset. Only drawback was clearance was tight with the biggest tires... I ran a Geax Seguaro 2.2 comfortably, but probably couldn't go much bigger while maintaining some mud clearance.

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  8. #8
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    [QUOTE=Spastook;8941198]
    Quote Originally Posted by jten9 View Post
    "Optimum" depends on the a-c length your frame was designed for... I used this article as a guide Making Your Own 29/26er | Dirt Rag Magazine in dirt rag to convert a bike a while back.


    Thanks, I read this article from Dirtrag and based on their formula it looks like a 425mm axle to crown measurement would work best for me. The White Bros. fork I've looked at is available in that length.
    Cool, I really liked my 69er, I wouldn't hesitate to do it again. Post a pic when you're done!

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  9. #9
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    A great option would be an OS Bikes Black Buck fork. They come in the following lengths:

    435mm AC with 51mm offset
    455 mm AC with 51mm offset
    475mm AC with 51mm offset

    You can get one for around $100.00 or so plus shipping.

    I got one a few weeks ago from Mark Slate and it is a nice fork and the offset would be good for a 69er conversion.

  10. #10
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    Doesn't more offset on a fork give you more trail?


    Quote Originally Posted by Andy R View Post
    You could use something like a Salsa Cromoto 425mm a/c, that will still give you more than enough tyre clearance for something like a 2.35 Rampage. However, I think that the 38mm offset of that fork (and most other forks intended for 26" wheels) isn't sufficient for optimum handling with a 29" wheel, so you end up with too much trail resulting in that "floppy" feel at low speeds.
    If you can live with 445mm a/c then the best fork you could get (IMHO) is the fork that Singular Cycles use on the Hummingbird 69er (and also the Gryphon, I believe).
    This has 55mm offset which works far better with the bigger wheel, as it gets the trail back down to a sensible amount and, as a bonus, gives fewer problems with toe overlap too.
    Nicest steel fork that I've ever used.

  11. #11
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    Quote Originally Posted by racewrench View Post
    Doesn't more offset on a fork give you more trail?
    No. Read this and it has nice pics to show you why... Dave Moulton's Bike Blog: Trail, fork rake, and a little bit of history

    To the OPer, I am currently using the Ragley carbon fork with 440mm A/C and a 38mm rake. I was using the Salsa Cromoto 445mm and find that my steering is a bit quicker with the Ragley even with less rake. I don't experience any flop and it is nice and responsive. I do think that my Soul Cycles Hooligan was built around a 100mm fork though. And i'm running a 650b in back.

    Basically, if you're building on a 80mm fork (about 430mm with sag) then you want about 410-430 A/C for rigid. The slightly slacker head angle will help on the downhills on a rigid. The larger wheel up front will also help this. I find more confidence riding rigid with the big wheel up front on the downhills. No suspension to compress and steepen under hard braking and turning into the corners.

    Trial and error and your riding style will decide how many forks you use to find your perfect fit. I've gone through 3 setups so far. I think i found my fork range. 440-445mm A/C and 38-45mm rake.

  12. #12
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    thx
    should have known that..

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