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  1. #1
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    72 deg. seat tube legs with a 54 cm top tube torso, help

    I did a bike fit through compettitve cyclist and started to get a picture of my poor proportions. I'm 5'10 with a 33" inseam, but my thigh is 23" by itself (from butt to knee cap as described on their site, flat back to the wall). when I pedal, my knee caps literaly reach past my shoulder blades in the drops(my back is flat, not arched). my current bike has a 73.5 deg. seat tube angle and a 55 cm c-c virtual top tube(head tube is also 73.5). the post that comes with my bike, a streampost, is proprietary and can't be swapped for more setback(its at least 15mm anyways). I'm riding a bontrager r saddle, and based on the wing position versus rail position, I don't think changing saddles is going to make much of a difference. my current stem is 100mm, but I dont think Im far enough back, meaning I would need a shorter stem. I don't really want to do that. any ideas on a 72 deg bike with a short top tube? even considered a womans frame figuring on a shorter top tube compared to seat angle, but thats not the case. a 73 or 74 deg frame would work with a very short top tube, 54 tops for a 73, 52 tops for a 74, because a deep offset post will lengthen the top tube. open to suggestions. thanks

  2. #2
    OM boy cyclezen's Avatar
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    Quote Originally Posted by Keithm View Post
    I did a bike fit through compettitve cyclist and started to get a picture of my poor proportions. I'm 5'10 with a 33" inseam, but my thigh is 23" by itself (from butt to knee cap as described on their site, flat back to the wall). when I pedal, my knee caps literaly reach past my shoulder blades in the drops(my back is flat, not arched). my current bike has a 73.5 deg. seat tube angle and a 55 cm c-c virtual top tube(head tube is also 73.5). the post that comes with my bike, a streampost, is proprietary and can't be swapped for more setback(its at least 15mm anyways). I'm riding a bontrager r saddle, and based on the wing position versus rail position, I don't think changing saddles is going to make much of a difference. my current stem is 100mm, but I dont think Im far enough back, meaning I would need a shorter stem. I don't really want to do that. any ideas on a 72 deg bike with a short top tube? even considered a womans frame figuring on a shorter top tube compared to seat angle, but thats not the case. a 73 or 74 deg frame would work with a very short top tube, 54 tops for a 73, 52 tops for a 74, because a deep offset post will lengthen the top tube. open to suggestions. thanks
    er, not poor proportions - great proportions!
    lotsa leverage and less useless upper body to drag around...
    same story for me, maybe a little more, since I'm about 5'10" 1/2 and almost 34 inseam and almost 24" thigh.
    ... you're getting to0 wound up in the short torso thing...
    long legs (and thigh bones) usually also comes with long arms... also a good thang
    which means OK for fairly normal frame Dims.
    I ride with 30.3 cm setback from BB to sitzbones - thatz about 6.8 cm saddle nose setback from BB, using a Spec Alias saddle on 56CM Roubaix. I also use a 120 stem. The Roubaix has 73.25 ST angle and a 56.5 TT.
    works great for me...
    the more lean angle you get to the upper body (to a point- about 45 deg), the further back your hip sockets rotate, relative to the sitzbones.
    175 cranks + 30 cm setback just about puts my tibial tuborosity above the pedal spindle.

    to my mind, too many riders these days are too balled up on their machines...
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  3. #3
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    Quote Originally Posted by cyclezen View Post
    er, not poor proportions - great proportions!
    lotsa leverage and less useless upper body to drag around...
    same story for me, maybe a little more, since I'm about 5'10" 1/2 and almost 34 inseam and almost 24" thigh.
    ... you're getting to0 wound up in the short torso thing...
    long legs (and thigh bones) usually also comes with long arms... also a good thang
    which means OK for fairly normal frame Dims.
    I ride with 30.3 cm setback from BB to sitzbones - thatz about 6.8 cm saddle nose setback from BB, using a Spec Alias saddle on 56CM Roubaix. I also use a 120 stem. The Roubaix has 73.25 ST angle and a 56.5 TT.
    works great for me...
    the more lean angle you get to the upper body (to a point- about 45 deg), the further back your hip sockets rotate, relative to the sitzbones.
    175 cranks + 30 cm setback just about puts my tibial tuborosity above the pedal spindle.

    to my mind, too many riders these days are too balled up on their machines...
    Your right, they are good proportions for cycling, but it seems most companies make bikes for the "average" rider. I actually liked riding with 6 cm setback from the bb to nose of my bontrager r saddle, but even when adjusted for new proper seat height, my lower leg looked axaggeratedly angled back. I studied many, many pictures of professionals at the bottom of the pedal stroke (I know, I'm not a professional) and found that 99% found a very similar, nearly perpindicular lower leg position at the bottom. I'm trying to replicate that for my position because it seems they're on to something. Fabian was an exception, his seat was a little more forward relative to the others. right now my seat is 8 cm back.
    thanks for the reply.

  4. #4
    Time for a change. stapfam's Avatar
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    Sounds as though your problem may be getting the saddle far enough back on the seat rails. I have the reverse with short thigh bones for my height of 5'6". I like a top tube length of 53.5 cms and find trouble getting the seat far enough forward. I would like a steep angle of 74 deg on the seat tube and I can only get this by going to a frame size that is too small for the TT length I want. I overcome this by using an inline Seat post that allows the saddle more forward movement.

    But in your case- You want the Seat further back - if I understand your underlying problem. There are seat posts that have a bend in them to move the seat rearwards.

    Other than that- I think you are looking at custom frames.
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  5. #5
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    Yeah thats right. but my bike came with an aero post design, called a stream post. BMC only makes one offset for the streampost, which looks to be about 15 mm.

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