Originally Posted by Maelochs

To really test friction under load, one would need to be indoors, on a machine, with force carefully controlled, so that friction could be measured precisely ... and tests would need to be 1000's of km long to measure the effects on wear .... and atmospheric/environmental conditions would need to be simulated, with some kind of calibrated grit-thrower and dust-blower and rain-sprayer ..... And No one Cares that much.