Set aside your wheels, 4 wheel bearing's, wheel shafts and the gear ratio of your choice. For this guide, i will be using the 3:5:1 ratio, which is the green counter gear ( not in picture ) with the pink shaft gear and narrow large diameter wheels.
Insert the wheel bearing to both sides of the nose unit like the picture below. Making sure the flared end of the bearing insert faces outwards.
Thread the shaft into the wheel bearings with the pink shaft gear in the middle.
Push a wheel into the shaft on both sides. Make sure the wheels are in all the way but not so tight that it cant spin freely. A good practice is to leave a ~1mm gap between the wheel and the bearing.
Give the wheel a quick spin and it should be able to spin for more than 10 seconds, if it does not spin freely check the wheel if its too tight or check the gear if there is something catching on the gear. Also watch the wheels as they spin. If there is a major wobble while it spins replace the wheels. A slight wobble is negligible but it is always best to have the wheels spin as straight as possible for maximum performance. Once everything is done repeat the same for the tail unit.
Keep Pushing the Speed
Reggie