I own a Cervelo P4 and have been using a Mavic disc with it for the past year.  Zipp just introduced a new disc, the Super 9, that is supposed to eliminate all of the fitting issues it has had with the Sub 9 and yet still be as fast.  However, on the Zipp web site, it issued a warning that it may not be compatible with some bikes that have hidden rear braking systems.  Does anyone know if this wheel is compatible with the P4?  Thanks.

Yeah, this is very very P4 frame/wheel specific. I have heard that if you shave the brake pads and can manage to open the brake arms wide enough without hitting the chainstay, the wheel can be used, even then it may work for some, not for others.  The problem is the increased width of the wheel.

I wouldn't consider buying anything other then a flat disc wheel for the P4 unless something new comes out from Cervelo about it. (Edit - although I can't see a flat clincher disc in Zipp's line up, so the 900 Clincher I think if you wanted to go with Clincher is near flat???)

 The P4 was designed so that it wouldn't need the tiroidal discs at all. It was maximised for flat discs. It is my understanding that as it was designed to be maximised for flat discs the P4 is fastest with a flat disc. In other words, no matter what the wheel company says about their wheels, the P4 is fastest with a flat disc.

 I've never seen a P4 ridden by the test team with anything other then a flat disc.

 the tiriodal bulge helps smooth the flow on some bikes - the P4 frame does the job in this case, you just don't need anything other then a flat disc so I am led to believe. 

 Open to corrections though, but I'm yet to see anything new in the P4 that would indicate it's changed re this.

 Thanks-appreciate all of the information.