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  1. #1
    Parts Guy Gravity Worx's Avatar
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    Need help in clearing up a frame building question

    We could use some expert frame builder information please.
    Thanks in advance.

    Here's the situation.
    We have a member (APclassic) who is contemplating cutting a head tube to make it fit in-between the 2 clamps on a Lefty fork. It has upper and lower crowns.
    Bottom crown is in fixed location, top one is obviously maxed out, hence, the need to cut head tube.

    I spoke up and said that the location of the cut (top or bottom of head tube) can have a slight effect on head angle.
    Was promptly, and in no uncertain terms, told that I'm stupid for even thinking of this.
    I'm OK with that part as that is just part of forums, However, I'd like to get the actual answer.

    On the bottom of page 2 and on page 3 we have diagrams (I'm a horrible artist so please bare with me)
    Can some one please prove or dis prove that this will have a slight effect on head angle?
    Here's the link:

    http://www.bikeforums.net/showthread...=1#post4084018

    Thanks again,
    Darin

  2. #2
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    OK, I think you are right. There will be a difference in the effective length of the legs if you shorten the top of the steering tube/neck, and the legs index from the underside of the top triple clamp. That difference in leg length means a difference in steering tube angle, however small.

    It might be possible to adjust for this change, if one had the parts in hand. It would also be worthwhile drawing out the change in trail to see how significant it is. Most bikes don't have enough steering tube extending above the TT to allow much change in the steering geometry from trimming back the top of the steering tube.
    Last edited by NoReg; 03-22-07 at 03:16 PM.

  3. #3
    Parts Guy Gravity Worx's Avatar
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    Thank you.
    That's what I thought, but wanted to make sure as my experience is more in assembling the bikes and riding them than it is in the frame geometry.

    Thanks again, darin

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