Sport riding performance on racing circuits and other locations is seen as an important element in the marketability of motorcycles. In sport riding, some riders start a turn while braking or start acceleration (driving) while turning. Furthermore, the braking aspect of sport riding performance is also critical to accident avoidance performance since it is similar to that of the braking during cornering performance. Consequently, in this paper a fundamental study was carried out to determine methods for improving the cornering limit performance during driving and braking. In the case of four-wheeled vehicles, the G-G diagram is used as a method to indicate the cornering limit performance. In the G-G diagram the longitudinal driving and lateral driving of the vehicle are set as the two axes. Therefore, the first part of this paper proposes a G-G diagram for motorcycles theoretically. In the latter part of this paper, this paper discusses the braking force distribution ratio of front wheel that would maximize the maximum lateral driving, the influence of the normal load distribution ratio of front wheel on the limit cornering property and the influence of the height of the center of gravity on it. From these result, this paper proposes methods for improving the cornering limit performance while braking.