Back in the saddle here at Moots.
Clearance on the Psychlo X newer stays can run a 34c tubular (read: big, fat) with some room. On my stock chainstay set up I can run a 38c Nokian studded tire during the winter and have great room. Like posted above, the tire makers are not using a standard and one's 34c is not going to measure the same as anothers. The 38c I run is on the small side for sure....but it is a good standard to start with.
I mostly run a 32c tubular or clincher and have good room for ice/snow/mud.
I'm writing a post on the bikes I used at nationals and will take good pics of tire clearance and get pretty indepth on what my set up was.