Originally Posted by grey_esp
I think the EL gt has a different front spindle than the regular Falcons, was done to get bigger and wider rims on there from the factory.
The spindle / upright assy was changed to fit the bigger brakes, the offset and other dimensions are still the same as a std falc.
A friend of mine had 10in wide rims on his EF, they fit nicely under the rear, but the front guards had to be rolled out even then they still touched on tight turns, but it can be done I guess.
As far as diameter goes the bigger the wheel the more component clearance you'll have.
Myself personally, I wouldn't go bigger than 18 x 8.5's with a 245/40/ZR18 tyre.