I'm 5'6.5" with a 29" inseam. I've been given the opportunity to purchase a p3C 48cm for an extremely good price. I'm having a hard time finding a 48cm p3 at the LBS to test to see if I would fit on it. Any input would be appreciated.
There's no way to tell for sure, unless you get fitted.
For a road frame, the generic formula is 0.67*inseam so your ideal road frame size based on that would be 49.5 cm (give or take). Most riders fit on smaller TT frames so you could fit a 48 cm P3 in theory. Will you? Go and try it out. There's no substitute for fitting.
Most riders fit on smaller TT frames so you could fit a 48 cm P3 in theory.
Actually the designers at Cervelo were feeling giddy one day and they decided to make the numbers based on the road bike size so the numbers would be the same. so a 58 of any road bike should fit the same sized person as a 58 Cervelo TT frame.