A gearbox assembly includes a plurality of planet gears. At least one planet gear of the plurality of planet gears includes a layshaft. The gearbox assembly includes one or more roller bearings disposed within the layshaft and includes a plurality of rolling elements. The gearbox assembly also includes a bearing radial envelope in a range of 1.2 to 4.325. The gearbox assembly can also include a layshaft axial envelope in a range of 3.8 to 12.5.