I'm running 215/65/16 chunky Michelin Latitude cross on mine. At the back there is about 1" clearance for/aft on the bottom of the arches. At the front it's about 1 1/2"
This is my first T4 and haven't played about with wheels much but I don't think I'd like to go much bigger. Though I think someone on here fitted 225/60/16 BFG's
Stick you tyre size into a tyre calculator and see how the diameter works out,
Ive raised the back with HD 1200 springs and wound the front up to suit.
I think the factory 16" T4's had different front arches.
Tobes