BMW i8. Click image to enlarge
Since carbon fibre is so incredibly strong, the monocoque design for the i3 and i8 will be completely rigid. It is so strong in fact that the structure can make do without any extra crash worthiness protection additions, thus further reducing weight. When a carbon fibre vehicle is crashed, it is more flexible than steel or aluminum. The fibre ‘net’ absorbs a lot of the crash force as it flexes, then releases it in a rebound.
The added rigidity also allows no ‘B’ pillar on the i3 concept car and thus permits a large, dual-door single passenger entrance area. With less space eaten up from the actual structure, carbon fibre–built vehicles allow more interior space so that a vehicle that borders on city car sizing, like the BMW i3, can offer interior space closer to a mid-size sedan. Finally, the carbon fibre chassis can accommodate a secondary engine (range extender) in the i3 as an option, without any need to vastly modify the structure.
BMW Carbon Fibre Plastics. Click image to enlarge
BMW expects production versions of the hybrid i8 to come in around 1,480 kg and knows it would weigh considerably more with conventional steel and aluminum architecture. For example, the 1-series based all electric ActiveE is close to 1,814 kg compared to the automatic equipped 128i that only weighs 1,490 kg. The real question then becomes how much will it cost. That has always been the stumbling block with carbon fibre. If it were cheap, every car in the world would most likely use the material. It will be interesting to see where the i3 and i8 end up on price once they hit the market. All BMW is currently saying is that the i3 will start below the price of a BMW 5-series.
However, with BMW investing heavily in carbon fibre plastic research and production, one can only hope raw material and production costs will decrease in the future. If the i car concept really takes off, other manufacturers will likely follow suit and join BMW in the carbon fibre plastic game which will only expedite the transition of carbon fibre from an exotic resource to an everyday material.