Over-tightening a flat-seat nut can deform the wheel, causing the aluminum under the washer to extrude, which displaces the aluminum, causing the nut to loosen.
Over-tightening can also stretch the wheel studs or wheel bolt shanks beyond their elastic range. All bolts or studs are designed to stretch a miniscule amount when optimal clamping load is achieved. This elasticity of the stud or bolt is what helps to secure the wheel on the hub. When torqued to specification, this is referred to as achieving the proper “clamping load.” If the stud or bolt is excessively over-tightened, it’s possible that it will stretch beyond its yield point, losing its “rubber band” effect.
If stretched beyond the yield point, the stud or bolt becomes so weak that it cannot provide the clamping load needed. The result: The fastener loosens or the stud or bolt shank breaks.
Always follow the torque specifications listed by either the vehicle manufacturer or by the wheel maker.
Don’t guess. Actually take the time to pick up a calibrated torque wrench and tighten all of the wheel’s fasteners, in the proper sequence, in several steps to achieve final (and equal) torque values.
As far as thread preparation is concerned, make sure the threads are clean and free of dirt, grease, grit, etc. As far as wheel fastening is concerned, specifications are generally listed based on dry (no lubricant) threads.
Applying oil, grease or moly to the threads will result in inaccurate torque values (you’ll end up over-tightening). Simply make sure the threads are clean and dry. Aluminum wheel nuts (found on some higher-priced imports) are typically made from a very dense, strong 7075 alloy, and will function properly if handled correctly.
And especially when dealing with alloy wheels, it’s important to re-check and re-torque all fasteners after about the first 50 to 100 miles of operation. Due to metal compression/elongation and thermal stresses, the clamping loads may change during initial use.