Botched geometry. Any suggestions?- Mtbr.com
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  1. #1
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    Botched geometry. Any suggestions?

    Basically a custom ti softtail frame with a number of issues, most recently discovered and most serious seems to be a geometry issue. Specifically head angle. Original thread is here in the 29er forum. Any ideas on a solution or how I should approach this would be appreciated.

    http://forums.mtbr.com/29er-bikes/mo...ma-767931.html

  2. #2
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    My opinion is: unless you know a few other tube angles of the frame, you pretty much have to take the builder's word. I don't think one can really measure a frame (angles) without knowing the rest of the frame's specs.

    So many things on a built bike can alter the designed geo (many were mentioned in the referenced post......axle to crown, tires, wheels, lower headset).

    You do have some ability to dial in the feel even if the frame is wrong. Items like fork (in terms of rake), tires, stem length, bar width.

    Head angle is just a part of the feel of the bike, and at the end , its just head angle. There are other geo items that together product the feel.......which lastly can be a bit subjective.

    I would ask for complete frame specs so you can reference against the head angle. This way, you are armed with the best information available.

    I liked Walts suggestion of putting an angle finder on the two bikes but that will only give you a comparison of the two bikes in their current build state.

    my contribution and good luck-

  3. #3
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    Only way to fix it is with a longer travel fork or a head set with a taller stack or a "slackset " head set.

    Tim

  4. #4
    pvd
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    Sell the bike.

  5. #5
    Randomhead
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    all of the possible solutions available to you (that are allowed by forum rules) are outlined in the other thread.

  6. #6
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    Seems pretty simple to me. If you had a custom order for specific geo and the bike does not measure out to that geo (give or take a reasonable amount of tolerance) then they need to re-do the frame.

    Pull all the parts off and find a local builder with an accurate jig. Have them put the frame in the jig and document all the angles.

    If it doesn't match what it's supposed to then Dean is at fault.

  7. #7
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    So I figured I'd echo this post here to see what you frame builder types think about the solutions here.

    Dean has elected to try to modify the frame to change the headangle. What they want to do is move the shock position forward on the top tube and remove some of the preload in the rear stays (this is a softtail afterall and has about 1/4-1/2 of it's travel preloaded into the stays.

    He thinks, using this method, that he can get the head angle (after sag of front and rear shock) to be about 71 degrees. This will also lower the BB... just not sure how much.

    So basically if they slacken the HA by 2 degrees by adjusting rear shock position, how much BB drop is this going to add? Also, do you guys think this sounds like a quality solution?

  8. #8
    pvd
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    It all sounds so horrible. I wouldn't want a hacked up frame like that.

  9. #9
    Frame Building Moderator
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    No.

    They need to start over. The solution being proposed will slack back the seat angle as well, which is going to totally change the fit of the bike in a number of ways. You can get your position to where it was by sliding the saddle WAY forward (~3cm) and using a 2-3cm longer stem, but it's going to result in a very odd weight balance between the wheels.

    Additionally, you're talking about a drop in BB height of at least 1cm and maybe 1.5cm (I'm not going to sit here and calculate it out, but it's going to be in that ballpark). That is a ton, especially on a full suspension bike.

    They need to start over from scratch, or you need to do an angleset type solution. Lowering the rear end of the bike is not a good idea.

    -Walt

    Quote Originally Posted by h2otaco View Post
    So I figured I'd echo this post here to see what you frame builder types think about the solutions here.

    Dean has elected to try to modify the frame to change the headangle. What they want to do is move the shock position forward on the top tube and remove some of the preload in the rear stays (this is a softtail afterall and has about 1/4-1/2 of it's travel preloaded into the stays.

    He thinks, using this method, that he can get the head angle (after sag of front and rear shock) to be about 71 degrees. This will also lower the BB... just not sure how much.

    So basically if they slacken the HA by 2 degrees by adjusting rear shock position, how much BB drop is this going to add? Also, do you guys think this sounds like a quality solution?

  10. #10
    Nemophilist
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    Geez;

    I still do not know with any certainty that the frame is wrong, but the fact that they would entertain the idea of "working around" a problem such as this means they have accepted it as a possibility. I'm gonna have to agree that this all sounds like a real boondoggle. I would not want a frame that I paid good money for to be bodged to make up for a clear mistake. I don't like the sound of it in theory, nor do I like the solution from a geo standpoint. It seems to me the only way to fix it properly would be to redo the HT, and I would think that would necessarily alter other parameters like the TT length in a manner you may not like.

    At this point I'd want WHAT I PAID FOR.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  11. #11
    Eric the Red
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    Dude, a lower bb will be miserable on your home trails. Make him fix that **** right.

  12. #12
    Stokeless Asshat
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    By all rights Dean should build you a new frame. Sucks but it's true.
    Zip ties? Not on my bike!

    Want:
    650B rims or wheel set. 80's vintage 32 or 36 x 135mm

  13. #13
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    Can you get your money back?

    Tim

  14. #14
    gran jefe
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    If he says its a good frame, then he will probably be willing to buy it back. oh, he won't buy it back? it's because he knows it's botched. ridiculous.

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