Ball bearings should always be your first upgrades; that reduce friction for less rolling resistance, and that means higher speed and longer the running times. Ball bearings hardly require maintenance and last a lot longer than stock Oilite bushings.
Our Yeah Racing Ball Bearings have the lowest resistance. They are manufactured perciously by Aircraft quality stainless steel. Pre-lubricated with light protection oil, not any grease to ensure its excellent performance!
Link: Yeah Racing