Everyone wants lighter cars, they provide faster acceleration for the same power, use less fuel and they create less damage to the road surface.
But lighter cars, perhaps build from carbon fibre aren’t better in every aspect.
For instance if we only look at the mass of a car in the situation of a crash.
When we take a look at car to car collisions, lighter cars fare worse than heavier cars. In a study from Boehly and Lombardo they found that there was an increase of up to eight times in the fatality risk for occupants between the smallest and largest cars in the US. Nygren in Sweden found that drivers of 800 kg vehicles were twice as likely to be injured as drivers of 1400 kg vehicles. This is a significant difference, but these numbers don’t address important design choices as structural stiffness and geometric details. So getting into a big heavy car will be good to protect yourself, but it will not be beneficiary for other people in lighter cars.
One way to counter this problem is by making cars larger. This way, with the use of the right lightweight materials it is possible to make cars which are lighter but also larger than a normal (steel) car and thus as safer. Larger cars can mean larger ‘crumple zones’ which are very effective in protecting the passengers and drivers in a crash.
In the following little clip you can see the effect of mass in a collision. This is shown by crashing a smart into a Mercedes E-class. The Smart has a curb weight of about 800 kg and the E-class has a curb weight of about 1500 kg.
So this is an important thing to remember when car constructors are building lightweight carbon fibre cars. They have to think about the reduction in weight and what it means to the safety of the occupants. This can be done by making cars larger, with larger crumple zones but also by using techniques from Formula 1 and building strong carbon fibre life cells.
But what about the old heavy cars who are still on the road?
Source:
http://www.thecarconnection.com/news/1049212_are-larger-heavier-cars-safer-than-smaller-lighter-ones
Carbon Fibre Monocoque 