Steel "Integrated Seat-Mast"...Good Idea?
I've been perusing the Giant bicycle catalog and their high-end road-bikes have "integrated seat-masts", which basically means the seat-tube doesn't stop at the top-tube and keeps going up, serving as the seatpost. According to them it's "stiffer", but it's only an option on CARBON frames, which is why I am asking the following...
If one were to go with a custom steel frame, would this option increase stiffness and/or help with racing performance, or is going with a standard alu/carbon seatpost system a better way to go? Obviously you would still need a seatpost binder at the top with a severely cut-down alu/carbon seatpost to get the saddle attached to the frame (unless you welded the seatpost binding system to the seat-tube?). Seems like it would be more weight than a traditional seatpost setup?
I ask because I am considering going with a custom steel frame from a local framebuilder and I might as well go balls to the walls with the design and an integrated seatpost would look awesome! :p
I also desire a triple-triangle setup, and with an integrated seatmast, well...it'd definately be unique. ;)
integrated seat post stiffness
Indeed, they are structurally stiffer.
However, with a round pedalling stroke, the seat between your legs is right at the end of the "lever" that it is (that keeps your bottom bracket from swaying from side to side), hence you wouldn't be gaining any actual pedalling efficiency from it. (plus the dowtube contributes immensely to keep the BB in place)
I do see a reason for carbon frame manufacturers using this setup: although I've never seen a survey or test data on this, I do suspect that carbon tubing is rather sensitive to compression! It may be good for general rigidity-to-weight ratio, but the mere nature of it's construction makes it poor at resisting strong forces squeezing it, such as a seat clamp! So it definitely has it's place in the carbon world.
However, the drawback is that the bike becomes hard to sell, because it's really made to measure for you. Also, you better make sure you get it right the first time, because contrary to a seatpost, there isn't much adjustment possible there. Once it's cut, that's it!
As the other guy said, marketing-wise it is a good way to give a blow to the pre-owned bicycle sales and increase new bike sales...
One thing though, this definitely does NOT have it's place on a custom steel frame! Do yourself a favor, kill that thought.
If you're looking for more rigidity, you'll gain infinitely more of that with a ROUND downtube and seat-tube (stay AWAY from "aero tubing, stay away from clover or triangular cross-sections, because that IS 100% marketing and 0% sanity), and possibly extra wall thickness too. If you go carbon, a frame such as a Merkx with extra material around the bottom bracket is the way to go.
If you would like a nice vintage ultra-stiff bike, I have a Cannondale for sale. I have too many bikes, just bought a recumbent, and my knees and back don't forgive me anymore for serious riding or racing. The Cannondale is equipped with the lightest components available in the 90's (no not Campy S-R, lighter than that!) but not as light as the new stuff available to the pros today.