beagle, did that 5.5 come with that shock? I ask because the SPV shocks are not generally the best match for VPP bikes. You're gonna get some differing opinions on this, but the VPP design needs very little stable platform for pedaling efficiency. Of course, there is personal preference, and it sounds like you want more of an "XC feel", so perhaps you'll be alright. While talking to Manitou a couple of weeks ago, the tech guy even recommended not using an SPV shock on my Nomad...which I wasn't considering anyway...as the inherent pedaling characteristics of the VPP on my Nomad would produce an overly harsh ride. I was ordering an Evolver ISX-6 which has no SPV platform. I've experimented with a couple of shocks on my Nomad, and we've had other VPP bikes through the shop obviously, and I have to agree that VPP bikes need little if any pedal platform...unless you're really looking for a stiffer ultra-XC ride. That's why the Fox Propedal shocks have often seemed to be a better choice for VPP bikes than Progressive and Manitou SPV shocks. The SPV is way stronger pedal influence than the Propedal IMO. This is apparently why Manitou is offering the Evolver series in a non-SPV design. The ISX-6 has no SPV, and the ISX-4 is available with or without SPV. Sounds like Manitou is recognizing the pedaling efficient designs like VPP, DW, Maestro and others.
On your 5.5 I'd use the minimum 50psi in the SPV chamber with the red chamber nut turned all the way out (counterclockwise) to start with. Set the main air chamber pressure to achieve the sag you need and go test. If you have bottomout issues, experiment with juggling a little more main chamber pressure and turning in the red bottomout chamber nut until you get the balance that you prefer. Try not to rely on the bottomout chamber anymore than you have to but definitely use it as needed to control bottomout if you're happy with your main air chamber sag and mid-stroke performance. Yeah, this a somewhat complicated shock compared to some "dumb" shocks that are available, but you should be able to get almost exactly what you want across a broader range of use. Oh...don't forget that as you turn in that red bottomout knob, the air pressure in the SPV increases, so you should check your SPV pressure and reset accordingly each time you change that bottomout knob. With your VPP design, I'd be surprised if you need more than the minimum 50psi SPV pressure...but it's there to raise if you need it. Remeber that SPV pressure is what affects pedaling platform and mainly that initial small bump compliance. On a VPP bike, you shouldn't need lots of pedal platform tuned into that shock or you'll get a harsh ride.
Sorry 'bout ranting.
