Does anyone know what 18" size wheels and tires will fit a 2011 G37x?

Tirerack.com says:
Rims that are 18x8 +40 will fit, but can I go to wider?
OEM tires are 225, can I go 235 or 245 without having to modify anything else (i.e. rolling fenders)?

I'm not looking for a staggered setup so I need specs that will fit both front and rear.

Thanks.