During the breaking-in period of a motorcycle, it is generally recommended to use mineral oil rather than synthetic oil. Mineral oil allows the engine components to wear in and seat properly, facilitating the break-in process. Synthetic oils, on the other hand, tend to have superior lubricating properties but may reduce the necessary friction during the break-in period.
It is important to consult the owner's manual or contact an authorized Aprilia dealer to confirm the specific recommendations for your SR 125cc model, as different manufacturers may have varying guidelines. They can provide the most accurate information regarding the optimal type of engine oil to use during the breaking-in period.