Replace the washers on your axles with Thrust Bearings to add just a bit more speed, efficiency, and reduce motor amp draw. It's not a huge gain, but could give you that competitive edge. And that's why it's only $1.70 per wheel.

On front wheels put between the wheel and steering linkage to reduce the friction rub. Do not put the cap nut on so far that it binds. Leave just a hair of play.

On rear wheels put between the wheel and cap nut / axle nut to reduce the rear axle spin. Rear axles are not supposed to spin and increase resistance on the motor when they slip in the chassis. Adding thrust bearings will reduce or eliminate this occurrence. Do not put the cap nut on so far that it binds. Leave just a hair of play.

Will not work on hollow rear axles.