Those tire size recommendations (no offense to MSA) are bunk.
In order to retain the same OD as what's on there now, I'd be looking for 225/55/16. Very common size, so there's lots of choices.
What you have now: 25.4" OD, 6.7" tread width
225/55/16 tires: 25.7" OD, 7.1" tread width
http://www.tirerack.com/tires/TireSearc ... iameter=16
Keep in mind, the Z can swallow up some pretty decent-sized tires. We run 255/45/16 on all four corners on our Z (of course, that's on an 8" wheel).