The change was first seen at Sepang, at the first tests for the new RS-GP 2018.
"Given the data collected over the past season and in keeping with the suggestions provided by the riders, we came up with guidelines for the evolution of the new bike.
Two of the objectives for the development of the Aprilia RS-GP 2018 were to focus the mass near the centre of gravity and to change the distribution of weight. These changes affected the entire bike, with several core components being moved and redesigned.
The fuel tank, for example, has a different shape compared to 2017 and it was physically impossible to keep the lid in the traditional position, which is why on the new RS-GP, access to the fuel tank is provided from behind the saddle".