1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
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  1. #1
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    Fork Length Question

    So I'm trying to build on a Kona Big Unit frame. Spec says fork length (axle to crown?) is 506 m.m.

    KONA BIKES | 2014 BIKES | TRAIL 29" HT | BIG UNIT (FRAME ONLY) Click on geometry

    When I look for carbon forks on sites like Jenson they are more like 470 m.m. I see no 505 m.m. carbon forks anywhere.

    So does this mean if I put in a 470 mm fork I alter the head tube angle and totally change handling of bike?

    Not sure what the 506 refers to on the Kona site linked above but again I cannot find a 506 mm rigid carbon fork in a search.

    Any help is appreciated

  2. #2
    Fat-tired Roadie
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    Yes, dropping 35 mm of length will mess with the bike's handling.

    Don't be overly specific in your search. Try looking for a carbon 29er fork. I bet it has about the right axle-crown length. 505 or 507 would be fine. Really, +/- 10 should be okay. But not -35.

    You could just buy the matching Kona fork. I bet Niner's carbon fork is about right. If you don't mind steel, there are a ton of nice options. Are you more driven by price or by getting to put some carbon on your bike?
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  3. #3
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    Quote Originally Posted by AndrwSwitch View Post
    Yes, dropping 35 mm of length will mess with the bike's handling.

    Don't be overly specific in your search. Try looking for a carbon 29er fork. I bet it has about the right axle-crown length. 505 or 507 would be fine. Really, +/- 10 should be okay. But not -35.

    You could just buy the matching Kona fork. I bet Niner's carbon fork is about right. If you don't mind steel, there are a ton of nice options. Are you more driven by price or by getting to put some carbon on your bike?
    Want a light build so I'm looking at carbon.

    Niner and others all seem to be at 470 mm

    Components > Forks > Rigid Forks | Jenson USA Online Bike Shop

    Im good with brakes, BB, crankset etc but the front end is a bit confusing.

    integrated, internal,threadless headset etc. Read up on it and Cane Creek has some good info but looks like Ill need help from LBS as far as headset as I suppose without proper press I'll mess things up.

    I could just ask LBS to get me a good fork but I want tolearn on my own if possible.

    Just cannot find a 505 fork. I may contact Kona about this.

    Lots to learn but I'm getting there.

    Any suggestions are appreciated. Just when I get ISIS, GigaX, square taper and JIS figured out I get the front fork curve ball thrown at me !

  4. #4
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    I think you will find that 506mm is the AC of a 100mm Fox suspension fork.
    Assuming it is sagged the usual 25%, that would be a AC of 481. 30% would be 470. The usual 29er rigid forks should work fine.

  5. #5
    rebmem rbtm
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    505 to 510mm axle to crown = a 100mm suspension fork
    Around 490mm axle to crown = a 80mm suspension fork

    I've seen 80mm suspension corrected rigid forks with listed axle to crown of 465 to 470mm
    I've seen rigid forks listed as 100mm suspension corrected with a axle to crown of 470mm
    Whisky Parts have a rigid carbon fork with 480mm axle to crown.
    White Brothers have a rigid carbon fork with 490mm axle to crown.

    If you're riding a 100mm suspension fork with the sag set at 20% it'll have a axle to crown length of 485 to 490mm, you won't be riding it with the fully extended length of 505 to 510mm

    http://www.universalcycles.com/shopp...p?category=703

  6. #6
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    Quote Originally Posted by Slash5 View Post
    I think you will find that 506mm is the AC of a 100mm Fox suspension fork.
    Assuming it is sagged the usual 25%, that would be a AC of 481. 30% would be 470. The usual 29er rigid forks should work fine.
    Thank you. Starting to make sense.

  7. #7
    Fat-tired Roadie
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    Interesting - the Kona Unit ships with a 470 mm Kona rigid.

    You could give them a call or email support. They're actually pretty responsive.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  8. #8
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    If you think about the bike's geometry, when you increase the length of the fork, the head tube angle is going to be increased. Say it's at 67 now, a lengthier fork could quickly turn that to 64. Doesn't seem like much, but your turning will feel less responsive and the balance is going to be a little awkward, especially at higher speeds.

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