How Often to Pack Wheel Bearings

In some respects it's a game of odds. My career of 40 yrs was in the bearing business so I know about bearings and proper lubrication. Your mechanic is right based on the way most all owners maintain their wheels. In between trips your rig will be stationary. The lubrication of your bearings is the oil in the grease. Think of grease like a sponge; grease is a sponge, wheel bearing grease is a lithium base, a carrier that holds the oil in place. Sitting for long periods, some of the oil will separate from the grease and when the wheels actually turn after that long period of being idle, there is a microscopic scar that can be made on the bearing raceway. That scar is like a defect on a blacktop road. Once it starts it grows faster as traffic runs over the scar and soon there is a pothole; or bearing failure. Rotating the wheels in storage will help prevent these scars from starting, as will taking the load off the wheels. As stated earlier, most will not do this so the best alternative is to repack annually. There are other factors, such as moisture due to changes in temperature and humidity that can affect corrosion rate. Temperature changes during storage can cause moisture to build and as that oil leaves the bearing surface they can start to rust. Again, microscopic in nature but can occur and cause premature wear and eventual failure.