Don't know about Navaras I'm afraid but can help with T2's.
Nothing but standard is recommended by Nissan, thats 235/75s on eother 15s or 16s depending on age.
Practically though a 31 x 10.5 will fit, though it dpends on the manufacturers sizing, I've got 30 x 9.5 x 15s on and neede to remove the front mud flaps otherwise they were fine.
What size have they got on?
For Navara try
www.uknissan4x4.com its a free site or the owners club in my sig.