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LFWD carbon mesh seat
Seats are one of the most difficult parts of bike design. I like mesh seats for their breathability, but generally they are heavy and kind of large (clunky) looking. I had been collecting ideas over the years, so for the new FWD I built the seat first. My first step in a design is doing 1/4 scale drawings and lots of dreaming - exploring the possibilities. Cardboard is then used as a mock up to see what the drawings can't quite show. The cardboard tube represents the large-diameter bike frame tubing.
Here is an underneath view of the bottom section of the seat showing a section of heat-formable foam replacing the right section of cardboard. The foam is heated with a hot air gun and hand-formed (using gloves). The foam is 0.25" thick FR 4305 Last-A-Foam. Supplier is General Plastics, Tacoma, Washington, 206-473-5000.
This shows the entire seat bottom section covered with one layer of 5 oz. carbon (inside and outside surfaces). This was not vacuum-bagged. Excess resin was squeegeed off using the moldless techniques. It weighs 8 oz. (230g).
Here the foam back section is temporally taped to the bottom and cardboard back for a check on shape and fit. The foam was easier to heat and shape in two separate pieces divided down the center, then eventually glued. The outside edges of the foam is then trimmed and sanded. It weighs 6 oz. (186g) covered with carbon.
A view of the fully carboned seat. At this point I attached the back to the bottom with aluminum brackets, thinking I might want to change the seat back angle. Later I removed the brackets and permanently joined the two with carbon. Mesh will be strung between the edges.
Here the mesh is being fitted. A dart is cut and sewn as the angle changes from bottom to back. The mesh is overlapped about 1.5" around the backsides of the seat edges. Masking tape covers this overlap so hole locations can be marked (~ 1" spacing on the seat bottom and 1.5"-2" up the seat back). Some darts have to be cut to accommodate compound curves. Then 0.25" diameter holes are punched in the mesh. To ease punching and to strengthen the hole area, epoxy resin was previously used only on the overlap. Hole layout is then transferred to the seat and drilled.
Here plastic binding screws consisting of one male screw and a female post are used to mount the mesh to the seat (very lightweight). Note the rear seat braces. I chose a low position closer to where high rider pressure (lumbar region) occurs, rather than have a long unsupported section from a top support.
Overall seat angle can be adjusted within a reasonable range by moving the attach points up and down the metal seat brackets. Spacers could also be added or removed at the seat end of the tube braces for further adjustment.
Seat bottom view showing hose clamps holding a split clamp (held on with two hose clamps) which permits forward/back location. The split camp was made from a 2" section of frame tubing cut along the 2" dimension and spread to slip over the frame tube. Two short 0.75" thick wall tubes are braized on the split clamp 180 degrees apart. Appropriate holes are formed in the seat bottom in line with the split clamp tubes. 0.75" tubes are carboned to the inside of the seat and butt up against the split clamp tubes. Then 0.685" diameter tubes are slipped through the 0.75" tubes, making a pivot support. This pivot allows seat angle adjustment.
Air comes in through the large front opening below the mesh (note the opening on the left side of the previous photo), passes up through the seat, cooling the rider, and exits out the vent. This hand-size outlet is a convenient way to lift the bike.
Here is the seat on a low FWD bike. Mesh supports the rider's bottom with about 0.75" of clearance to the frame tube. In the lumbar region the rider does contact the carbon for about 2" in from the edge. This is to prevent rider backward movement during power pulses and its resulting loss of power. Further up the back, the pressure is much less and support is through the mesh only. There is minimal lumbar curvature needed because of the semi upright seating angle (to see over a fairing). This mostly steel version bike weighs 24 lbs. and is designed to fit in a 6 lb. foam streamliner.
Comparing a standard type steel frame/mesh seat with the carbon/mesh seat. The frame type seat typically weighs 2 lbs. 8 oz. (not including seat braces). The carbon seat weighs 1 lb. 6 oz. The carbon seat is trim, stiff, yet it still gives the breathability of a mesh seat. I do use a crotch support mounted on the frame, consisting of a small piece of stiffish foam.
Next section: Origin of the mold