Originally Posted by fpmlt
Would one then also need to consider: tire pressure, load, shock type and setting, and even speed?
In my opinion, no.
I tried to be kind in my evaluation of the posts on the ADVrider site by the guy who reports having done a cement mixer stress test of a K1200rs final drive; this will be a little more direct:
Here's the salient part of this guy's post: "....cut top and sides; replaced with plexiglass. with highspeed flim 300 frames per sec. I placed red dye #3 in cage ball area. spun drive and struck wheel to simulate bump, all load was absorbed by cage twice once at impact and at 90 degrees later in spin direction. after 144 impacts the 92,997mi. cage failed in the same way as the 19,700mi. cage did. same test new 17 ball unit failed after 661 impacts in the same way as the 19 ball bearings. stay away from potholes"
Let me put it this way, I think it is either a very inadequately controlled test, or he lacks the ability or motivation to report it well, or the entire thing is a fabrication. In any case, his report gives me no valuable information, just questions. I mean seriously, he installed a window in the drive housing, filmed with "highspeed film 300 frames per sec.", and hasn't posted a picture, and can't write a better description than that? I'm waiting for pictures of his test rig, and a well written report of his findings. Until then, it is malarky as far as I am concerned.
I have 40K miles on a FD rebuilt with a 17 ball bearing. I have pounded over potholes, two up, overloaded with camping gear, ridden the "washboard" of the hardpacked dirt roads of rural Vermont at speed. My drive has been hammered. I opened it recently to inspect the bearing. After 40K miles it looks like new. That is just a case report of one, but frankly a better indication of things than is his reported simulation of potholes.
If this guy actually simulated 661 potholes and made a bearing fail, I'd like to know exactly what his experimental setup is, and I'd like to see good quality pics of the failed bearings after they've been cut open. Until he reports with good information it is meaningless. Let's face it, potholes aren't good, they can bend rims, and breakstuff, and maybe enough potholes hits will break a final drive. The mech. engineers who have kindly posted on this subject in the past have indicated that micro-stresses to the balls and races during installation or due to excessive preload may be what sets the stage for development of the pitting of balls and races that I am seeing in failed bearings. It stands to reason that if you hit the bearing hard enough you might initiate such micro-stresses eventually leading to failure. But I think that this is unlikely in a properly lubricated, properly assembled final drive.
So, an emphatic "NO", I do not think we need to consider: "tire pressure, load, shock type and setting, and even speed".
That's a considered opinion, but granted, just an opinion.