fork oil level

[DeanR]

I'm confused about how much fork oil to use. The folks at Progressive tell me to measure the level without springs in and with forks completely compressed. Level should be no more than 5 1/2 in measured from the top of the fork tube.

Well, after putting in 8 oz. per Yamaha manual ( 6 1/2 oz drained out that I had been running with ) I measure 11 1/2 in. from top of tube. Quite a difference and I don't know what to make of it.
The other fork which I haven't yet drained ( broken off drain screw ) measures 13 in from top of tube!
What's the deal with fork oil??

[TopCatGr58]

Well Dean,

I don't know about the folks at Progressive, but my understanding is that the amount of oil needed is just enough to cover the lower damping rod and its valving holes, and I would imagine that Yamaha calculated that when they set the recommended amount of fluid for the forks. The Progressive springs aren't much different than the OEM's in that they take up a certain amount of space in the tube, so as long as the fluid is up far enough to cover the damping rod, then I would think that would be enough, and probably doesn't need to FILL the entire tube to the Progressive recommended level!

Any hydraulic Xperts want to chime in, confirm or bust it?
T.C.