I currently own a GSF(1800kg) and recently rented a MX-5(1000kg). The first thing I noticed from that MX-5 was... Wow!!! It's so noisy!!! When I drove that little car on mountain roads, I didn't notice a lot of differences between both. However, when I filled up some gas for that MX-5... Wow!!! That's a BIG difference!!!
Very good material but one claim: "reducing the mass by 100 kg will result in a 7-9% reduction in fuel consumption - is not true." The material does not take into account the possibility of braking kinetic energy recovery. For example, a electric car with a mass of about 2000 kg will consume about 20 kWh of energy/100 km, but the same electric car loaded with 5 people and luggage and weighing about 2500 kg or 25% (500 kg) more - will consume only 1.3% more energy so about 20.26 kWh/100 km due to braking energy recovery. A heavier car will roll further downhill or recover more energy than a lighter one. It can therefore be said that: "a weight reduction of 100 kg reduces energy consumption by about 0.05 kwh/100 km". But the fact is that carrying a heavy chemical battery in an electric car is completely pointless.
Cars have not only become wider, but taller as well. Witness the rise of the SUV which has displaced sedans in many countries. SUVs are also more likely to have 4 wheel drive, which adds more weight to an already heavy vehicle. All the efforts of automotive engineers to achieve lighter weight are wasted when consumers buy the wrong type of car.