The carbon fibre seat base I ordered from the guys at Unicyle.com NZ arrived and looks great! Super light, much thicker than I expected and super rigid. The plan is to use the carbon fibre seat base as part of my XC handlebars for 36″s.
The CF seat base is blank – coming with no markings or templates regarding where to drill holes for the seatpost, front and rear bumpers. It’s a little intimidating as you don’t really want to screw up a new CF base!
I used a plastic KH front bumper to roughly mark out where the front holes should be, then used a KH brake bracket for more accurate marking of the front holes (the plastic front bumper doesn’t sit flush on the CF base whereas the brake bracket does), taping the bracket down to the seat base and checking it from all angles to make sure it was square before marking.
With the front holes marked, I drilled and filed the four holes as per the instructions on the NZ Uni site.
I then mounted a metal stiffener top plate from a spare plastic KH seat to the top of the carbon fibre seat base to act as a guide for marking the holes for the seat post. I taped the metal stiffener plate hard against the CF based, checking it was aligned with the centre of the seat.
So with the seatpost holes marked, I again drilled and filed them as per the instructions – 3mm hole first, then 6.5mm hole, then file out the corners to make a neat fit for the carriage bolts.
The metal stiffener plate turned out to be a great guide for the seat post holes. I had previously placed a seatpost against the underside of the base and marked out my best guess of where the holes should be. You can see how far off those markings were in the photo.
Finally I marked the rear bumper holes using a plastic KH rear bumper, this was the easiest one as the bumper sits flush against the base.
The carbon fibre base is much thinner than the plastic base, so with all the holes prepared I then discovered the bulk of the spare bolts I had from the plastic seat were too long.
20mm M6 bolts work for the seat post holes. In my case since I was mounting my own handle where the front bumper should be 20mm also worked there, though they may be a little too long if I’d been using a plastic front bumper. 20mm was definitely way too long for the rear bumper but the bolts were soon shortened with an angle grinding, being sure to place the nut on first so it could be removed after grinding and in the process repairing the burred threads.
It’s recommended that rubber be placed between your seat post and carbon fibre base to stop the front and back edges of the seat post damaging the CF base. Finally I’d found a use for the original 36 tube!
Before putting the seat back together I covered the bottom edge of the CF base with tape, to prevent the seat base from cutting the seat cover, and causing discomfort.
I’m really looking forward to taking it for a test ride and seeing how well it works with my XC handlebar project!