DW
a roto-molded seat is exactly that... it is a seat made by rotating the mold. Roto molding is commonly found in the plastics industry. the process starts by heating a aluminum mold and injecting plastic pellets (usually low melting plastics like polyethylene) into it, as the pellets melt, the mold is rotated to coat the inside of the tool, when the mold is thoroughly coated the heat is removed and the plastic starts to harden while the mold is still being rotated. After the plastic cools or "B" stages the part is released from the tool and hopefully sales are good enough to start the process all over again. Roto molded products are a cheep way to make a hollow cavity part without the expence of an internal core. Common roto molded parts beside seats are, kayaks, Jazz style fuel cells, trash cans, even some ceramic figurine's.
Composite seats including fiberglass and carbon fiber are still legal. well made composite seats will hold up to stresses, and vibration much better than aluminum! Have you ever seen an aluminum seat all cracked up around the mounts? Check yours it might be. That's why Kirky and other manufacturers triple reinforce all there alum seats in the mounting areas, they know they are prone to failure. My liner seats are all carbon fiber.
The question is about the tubing structure below the driver, not whether anyone thinks this seat is better than that seat or what might not be legal next year. Consider the seat like the hood of your car.... you can drive your car with out the hood... you should be able to drive your race car without the cosmetic seat! the cage should be tight around the driver and the safety harness designed so you ARE NOT relying on the seat for restraint. You should be able to set in the frame and harness and drive the vehicle without a seat. Last weekend Rick Vesco dropped off Don's bike liner the "Lightning bolt", Don Vesco raced and crashed this liner several times over 300mph.....That liner didn't have a seat.... never did..... and when we restore it....it never will.
Kent