Fitted Seat Tube - what sizes and options are there being used?
I have a design brief that requires the use of a seat tube extending 200mm above the Top Tube.
For those of you that have done this style of construction, my question is to do with sizing of the tube that was used, both tube diameter, wall thickness and whether sleeving has been used.
As to why, an example of using Columbus Zona External butt seat tube 28.6mm and seat stem (235gr) combo to yeild a saddle height of 810mm = 507gr.
Using a 35mm x 750mm butted 9/6/9 down tube = 470gr plus fittings. A similar result, but bespoke fitting to client only and no adjustment for height.
No doubt 28.6mm tubes are lighter as a combo, but my brief does not give me that option. Most seat tubes of the 28.6mm variety have .6mm wall with 200mm to go with external having .9-1.2 to work with at the upper 75-100mm. At any rate, can't get the 750mm required that way with off the shelf tubing.
My proposed option is to use a 34.7mm Down Tube that has .9 x 150mm with a 40mm butt taper to .6mm. This leaves 10mm of .6 before connection to the top tube. This area WILL be SLEEVED. So no sweat on Strength as I have the insurance of 35mm dia. plus...sleeve.
I would like to expand the information base as there is no info around to base decisions on.