Head Tube Length Q
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  1. #1
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    Head Tube Length Q

    I am 6' 1" with a 36.1" inseam. The top tube on my to be custom frame is 57.4 effective, the seat tube is 56.6 with a 5-6 degree angle. 814 cm bb to saddle top. The first drawing of the frame design shows a 21.8 cm head tube. What would you geometry experts say would be good head tube length based on my specs?

  2. #2
    What? Me worry?
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    Based on your height and inseam, you'd probably ride a 58cm frame in a race bike, maybe a 56cm if you went really compact, and a 60cm or even 62cm with conventional touring sizes. For a 58 cm frame, a head tube of about 190 is plenty big. 218 sounds excessive, particularly if you want to get any significant bar drop.

    Check the height of the bars vs. the height of the saddle and see if you can get the drop you want.

  3. #3
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    not enough info...

    To give a suggestion, you either need to post a desired handlebar height from the floor to the top of the bars or the desired drop from the saddle to the top of the bars and the BB drop, if it's something other than the common 7cm.

    A reputable builder would show all this in his proposal, so you know ahead of time exactly how much spacer and what stem angle was required to make the bike fit as desired. Without this info, the frame won't be very well customized.

    I would assume this frame uses a conventional headset that adds 25-30mm to the HT length, not an integrated type with a smaller stack height?

  4. #4
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    More Info

    You don't say if the frame in measured center to center or center to top. also you don't say if it's got a sloping or horizontal top tube. I am the same height as you. Using the conventional formula for frame size I need a 60cm frame (c->t horizontal top tube). This fits me perfectly (with the seat post all the way up), so the size you are talking about sounds very small. I don't know off hand what the center to seat top is of my bike is but it sounds to me like you would need to use an extra long seat post to get enough height. My toptube is 58.6 which is long so the length you describe is comparable for a frame of that size. The bottom of the head tube is at the same height on all frame sizes with the same wheel size. On a bike with a horizontal top tube the top tube meets the head tube at the same height as it is at the seat tube so the length of the head tube is proportional to the size of the frame. You don't say if you want to have high or low bars so it's hard to say if you are getting the right length of head tube. You certainly will be able to get the bars low enough with the geometry you describe. If you want high bars ie. as high as the seat you will need a humongous pile of spacers under the bars. Do you have unusual proportions like short legs and a long toro?

  5. #5
    kmc
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    parallel universes...

    tyro -
    Our measurements are really similar. I am 6'1-1/2" with a 36" inseam. My desired bb to seat height is 81cm, based on a fitting by a very good physical therapist in seattle who specializes in bike fit.

    My custom frame has a 58 top tube (with a six degree slope), 56.4 seat tube length and a head tube of 18.5 cm. With 20mm of spacers, I have 8cm of drop between my handlebars and seat. I specified the drop to the builder based on the fitting...he determined the head tube length based on my choice of headset, spacers, stem, etc. I am using a 110 x -6 stem as well.

    Did you specify any drop? If my bike had your head tube length, I guess I would only have 4 cm of drop.

    I hope this helps as reference. PM me or reply if you need any more information on my bike's numbers.

  6. #6
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    The bar drop is speced at 6.5 cm to start and if I flip the stem with the 2 cm of spacers, it would go to 9 cm. The fitter has all of the info in the sheet and then some. Right now the headtube with headset is 18.9 cm total. The stem will be run in the positive 6 degree rise position to arive at the bar drop of 6.5cm. The 21.8 cm ht length was to achieve the amount of drop with the stem in the negative 6 degree position. I think that the 18.9 cm total will be fine. This includes a 1 cm head tube extension (above the usual extension).

    The rest of my bike's numbers are st (c-c) 56.5 cm, tt (effective) 58.4 cm, ht 73.5 degrees, st angle 73, 41.3 cm chanstay, with 5 degree slope to tt.

    kmc, parallel universe is right! Seperated at birth! Thanks for the info on your frame. It sounds like our frames will be very near the same dimensions. Mine will have less bar drop to start, but that will be primarily baes on the way I will run my stem. One questions though, how far is ir from the BB center to the top of the saddle? I am at 81.4 cm.

    Thanks a lot for the help guys!

  7. #7
    kmc
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    info

    tyro -
    My bb to top of seat is 81cm. Also, my headtube is 18.5 without a headset. Add another 20mm for the headset. I am running 20 of spacers as well.

    Our bikes will be very close. My specs: seat tube 56.4, effective top tube 58, head tube angle 73.5, seat tube angle 72.75, chainstays 41.5, six degree sloping top tube.

    Who is building it? I got my Curtlo in February. Great bike.

  8. #8
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    Quote Originally Posted by kmc
    tyro -
    My bb to top of seat is 81cm. Also, my headtube is 18.5 without a headset. Add another 20mm for the headset. I am running 20 of spacers as well.

    Our bikes will be very close. My specs: seat tube 56.4, effective top tube 58, head tube angle 73.5, seat tube angle 72.75, chainstays 41.5, six degree sloping top tube.

    Who is building it? I got my Curtlo in February. Great bike.
    Yes, the bikes will be VERY close to one another. Let me know if you ever want to trade.

    It is being built by James at Black Sheep in Colorado. He's been an absolute pleasure to deal with in every way. I simply cannot recommend him enough. www.blacksheepbikes.com

    Curtlo does great work. He's local to me as well. I'd love to have one of his cross bikes.

  9. #9
    old school drop out
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    Quote Originally Posted by tyro
    I am 6' 1" with a 36.1" inseam. The top tube on my to be custom frame is 57.4 effective, the seat tube is 56.6 with a 5-6 degree angle. 814 cm bb to saddle top. The first drawing of the frame design shows a 21.8 cm head tube. What would you geometry experts say would be good head tube length based on my specs?
    That sounds tall to me. I'm about your height, with a slightly shorter inseam. On my bike, a 218mm headtube with an external headset, measures to about 1/3 of the way up the stem.

    I assume that the frame will have an integrated headset? If so a 218mm might be workable for me, but would require no spacers, and a -17 stem. But if you're looking for a more upright ride, it might be okay.

  10. #10
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    Quote Originally Posted by laffeaux
    That sounds tall to me. I'm about your height, with a slightly shorter inseam. On my bike, a 218mm headtube with an external headset, measures to about 1/3 of the way up the stem.

    I assume that the frame will have an integrated headset? If so a 218mm might be workable for me, but would require no spacers, and a -17 stem. But if you're looking for a more upright ride, it might be okay.
    Thanks for the info. I've talked him and we've gotten the ht down to 18.9. I think it should be fine there.

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