What's the fascination with trailer bearings?

rwbradley wrote:
I am not trying to be a troll and start something, I do check my bearing and tire pressure when I travel. Why because everyone says you should. But if you ask them why you should they tell you because everyone else says you should.

But it is funny, a number of months ago an almost identical thread came up about tire storage and it took several pages to get to fact when someone posted Michelin's official statement on how to store Trailers with ST tires.

I am genuinely curious about the answer and I have no opinion on it at this point, and having a lot of people say "just do it" is a good way to get an answer, but I always like to ask why before I decide.

But after 3 pages of opinion that you should do it. I only saw one person actually answer the OP's question "Why?" He said that maybe it is because of the type of bearing. Is there anyone who can confirm this to be fact or outline the logic of why it could be fact?
Thanks

I'm not a wheel bearing or grease expert but using my armchair internet skills I discover that "grease" is a semisolid lubricant. This means that it has an oil lubricant mixed in with something (usually a soap) to make it "thick enough" not to run out of the wheel. Getting it just the right thickness is called viscosity. When a grease sit's for a long period of time the "oil" tends to separate from the "thickener" which is the soap. Now this grease is not only supposed to lubricate the bearings but it is also trying to keep contaminates like water and dust/dirt from reaching the ball bearings and race surface. When the oil separates out of the soap there is an avenue for water or dirt to reach the bearing/race surface which causes rust to develop on the bearing surface. The ideal situation for a trailer is to have the wheels jacked up off the ground and every day you rotate the wheels by hand to keep the oil and soap mixed together well. Most people don't have the luxury (time) to do that but instead repack with new grease which has the correct viscosity to keep it optimum condition to 1) lubricate the bearing surface and 2) prevent ingress of contaiminates (water and dirt). If your trailer doesn't experience much water or dirt contamination and it does not move very often of very fast then the risk of bearing failure is reduced.