Reply #49: Composites are expensive to produce and -- particularly -- to repair.

[leveymg]

A typical F1 car is about 1200 lbs, but could be considerably lighter if the rules allowed. Of this, the carbonfiber/kevlar hull is less than 150 pounds. If you apply the same technology to the chassis of a roadgoing passenger car, one could scale up to a five passenger crossover with modest off-road 4WD capability that weighs 2700 poundsor less.

By the way, I own a 1st gen Miata, the dimensions of which are only a bit larger than a mid-'60s Lotus Elan, which it so strongly resembles. The Miata is 800 pounds heavier, primarily because its structure is almost entirely welded steel structures. The Lotus had a steel backbone chassis, but the rest of the hull is made of fiber glass. A similar design using modern composite material instead of fiberglass would be strong enough to pass today's impact requirements, but it would be very expensive to produce because the laminates are hand-laid and then baked in a vacuum oven.

But, here's the real reason we don't see more modern composites, except on very high-end sports cars: the insurance industry. A Carbon-fiber/kevlar tub is extremely strong and stiff, but once damaged, must be replaced in its entirety - it's practically impossible to repair any but the most localized damage.

It is possible to design a composite chassis, road-going passenger car/light truck with modular (bold-together) substructures. It would make the most sense, structurally, to bolt the front and rear subframes to a central spine (like the Elan) that is attached to the cabin hull. That would reduce repair costs, somewhat, over a monocoque, but the manufacture and replacement cost would still be more that pressed and welded sheet metal.