It helps to be familiar with frame tubing (brand and type) to have an idea of what you are dealing. Without decals it can be quite difficult (impossible) to determine tubing type, and decals are unfortunately often replaced with the incorrect one. Still, most higher end/lightweight tube frames use certain seat post sizes that generally conform to the wall thickness of the tubing used (at least the seat tube). If a seller says Columbus tubes forca bike w/o any decal then I would question how they knew what the tubing is. I would still ask for the seat post diameter (hoping the correct one is in place). That at least gets you in the ballpark; e.g. for Columbus Aelle=26.8mm, SP=27.0mm, SL=27.2mm; Reynolds and other makers follow a similar pattern, but of course there are always exceptions.
Note: larger frames tend to use thicker walled tubing so if you are looking for an extra lightweight frame you may only find them made with a slightly heavier tubeset or mixed tubesets than what small to medium frames use in their lightweight models.
Regarding the first bike shown with the Tretubi frame; that asking price is far too high. That is an entry level frame built for a specific price point and would not garner that high of a value unless the groupset/components installed were of a much higher grade (it does happen where high end groups are put on low tier frames by owners, but not on factory bikes. The tubing type does not dictate the quality of construction, but certainly should affect value since it is a less expensive frame regardless of components. The feeling and responsiveness will be affected depending on how hard you intend to push it. I have not ridden an Aelle Tretubi (Aelle main tubes, probably hi-tensile tubes elsewhere) framed bike so I cannot provide feedback on it, but an full Aelle frame itself rides well and is certainly stiff and durable enough. I like my Aelle framed bike better as a climber than an SL frame, and most else being equal (same rims, tyres, pressure, saddle) the two frames ride comfortably enough for hours in the saddle.
Note: larger frames tend to use thicker walled tubing so if you are looking for an extra lightweight frame you may only find them made with a slightly heavier tubeset or mixed tubesets than what small to medium frames use in their lightweight models.
Regarding the first bike shown with the Tretubi frame; that asking price is far too high. That is an entry level frame built for a specific price point and would not garner that high of a value unless the groupset/components installed were of a much higher grade (it does happen where high end groups are put on low tier frames by owners, but not on factory bikes. The tubing type does not dictate the quality of construction, but certainly should affect value since it is a less expensive frame regardless of components. The feeling and responsiveness will be affected depending on how hard you intend to push it. I have not ridden an Aelle Tretubi (Aelle main tubes, probably hi-tensile tubes elsewhere) framed bike so I cannot provide feedback on it, but an full Aelle frame itself rides well and is certainly stiff and durable enough. I like my Aelle framed bike better as a climber than an SL frame, and most else being equal (same rims, tyres, pressure, saddle) the two frames ride comfortably enough for hours in the saddle.
to old to change now……
