Hi Bonz, I'm basing that off of some things that Lake Speed Jr. has said about ZDDP--repeating that ZDDP tends to both increase friction and reduce wear in the right amounts (though if too high can cause more wear and/or damage).
I'm aware that at high temps, ZDDP forms a glassy phosphorus coating on metal surfaces. But is that all it does? Because I would think that would only tend to reduce friction, not increase it. I've wondered if in the particle state, it has a gelling like affect (sort of like, but different than, a polymer based viscosity index improver)? I wonder that for a few different reasons. One reason is that I was actually looking up reviews of a ZDDP increasing additive recently, and one of the reviewers noted that after he poured out the contents of the small bottle, there was left behind this thick, goopy, snotty like residue and he was wondering if perhaps that is where most of the ZDDP was actually at. (the product was a single bottle of Rev X on amazon btw).
Again, I'm no expert, but I do like to connect the dots and question. I have been trying to figure out what the difference between regular car oil and wet clutch motorcycle oil is for awhile now, and I don't believe it is solely as simple as motorcycle oils always have much less moly, boron, and/or antimony. But I may be wrong. But I do note a few major repeating patterns in the real world, 1. motorcycle oils tend to have higher ZDDP levels than car oils, 2. they have lower amounts of moly, boron, and/or antimony generally, and 3. they tend to be higher viscosity. And I have wondered if there is a synergistic affect from those 3 common differences? I'm fairly new to this whole "obsessing about oils" thing though.
I guess to know for sure, someone would have to consult a tribologist(s) who has been involved in formulating wet clutch motorcycle oils. It would be great to be proven correct or wrong on this. But I rarely ever hear anyone discuss the mechanics of why they are different, but just the repeated dogma of, "you can't use car oils in wet clutch motorcycles because". At most, I hear about friction modifiers, and yet I've seen some (even high quality Amsoil) motorcycle oils with decent levels of moly and/or boron. I've never been satisfied with surface level dogma, and have a need to know the exact why's.