Head tube angle change for Kona Unit- Mtbr.com
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  1. #1
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    Head tube angle change for Kona Unit

    I have a 2009 Kona Unit (small) with a head angle of 70.7 degrees. There is a handling problem with the front wheel wanting to wash out in corners. I'm running the standard Maxxis Ignitor 2.1s that came with the bike, currently at about 22-28 psi (depending on the conditions). I weigh about 70kg fully kitted out. I have tried many different (including higher) pressures, but the problem just gets worse. It just feels too slack. The tyres aren't worn much at all.

    I intend to try changing the tyres to Racing Ralph 2.4 front/2.25 rear to see if this helps. I realise this slackens the HA even further, but maybe the bigger front tyre will give more grip and eliminate the problem. It's certainly the cheapest option to start with.

    As you can see by the specs linked below, the larger sized Units have much steeper HAs (72.2 - 73.3 degrees).

    Is there someone out there clever enough to tell me what the new HA would be if I switched to a 445mm carbon fork (drops the front by 19mm)? I'm also aware it will change the seat tube angle and drop the bottom bracket a little.

    Full geometry specs are here > http://bikes.konaworld.com/09/09_unit_en.cfm but the other critical figures used to calculate should be the Wheelbase (1070mm) and current Axel to Crown of 464mm.

    Thanks in advance,
    Steve
    I see hills.

    I want to climb them.

  2. #2
    AZ
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    Less than one degree .

  3. #3
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    I've had that problem on another 29er. IMO, it's not your tires. Sounds to me like you've got a mix-matched fork in regards to trail or offset.

  4. #4
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    Calculation

    Quote Originally Posted by Stevob
    Is there someone out there clever enough to tell me what the new HA would be if I switched to a 445mm carbon fork (drops the front by 19mm)? I'm also aware it will change the seat tube angle and drop the bottom bracket a little.

    Full geometry specs are here > http://bikes.konaworld.com/09/09_unit_en.cfm but the other critical figures used to calculate should be the Wheelbase (1070mm) and current Axel to Crown of 464mm.

    Thanks in advance,
    Steve
    Based on those specifications, If you put on a 445mm fork, it will change the head angle to 70.94 degs. Not quite what you are looking for...

  5. #5
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    Thanks for the responses. The current fork is the standard one, with an offset of 45mm, pretty common, but gives a more pronounced effect when compared with the other head tube angles available.

    Looks like it's time for new tyres.
    I see hills.

    I want to climb them.

  6. #6
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    What about putting on a slightly longer stem so that you have more weight over the front end?

  7. #7
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    Sorry to hear that you are having problems.I have a 19'' Unit that I run a RR 2.4 on the front and I have no problems with the front end washing out. I don't think you can go wrong with it on the front and rear, but go 2.4 on both ends or else you will slacken the HT a little more. You have plenty of room for a 2.4 rear. I also think that the above post is on the right track with a longer stem but you can try just lowering you existing stem to get more weight on the front wheel. Remember to pay attention to keeping your weight up front and remember that winter trails are hard and icy and that things can change a lot for the better come spring.

    Here is a pic showing the rear clearance with a 1.9 Karma:
    Attached Thumbnails Attached Thumbnails Head tube angle change for Kona Unit-p1020476.jpg  


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