Why does A320 Main Wheel need to be tightened 3 times during installation?
FreeMan - Commercial jet aircraft wheels are installed with a single nut on the axle, like a wheel hub on a car.
The commercial jet aircraft axle is a few inches in diameter and is hollow. The wheel bearings are tapered, and while the axle nut is being tightened the wheel is spun ih the normal direction of rotation. A higher initial torque is applied to the nut, and the pressure on the bearings helps to get the races properly seated while the bearings are rolling over them.
The nut is loosened, then the process is repeated using the torque specs specified in the manual. 
One of the airlines I worked for had a policy that required that the final time the nut was tightened, it would be turned by hand. After a while, they went back to following the manufacturer's recommendations. 
To recap, really tight to seat the bearings, looser for in service operation.
I hope that helps.