Will a 20" X 8.5 wheel with a 45mm offset
Fit a 2005 GT without issues?

I know the 45mm offset is standard on stock GT wheels, but
Doesn't that change as wheel diameter Increases?

(Sorry dont really know anything about wheels)

Thanks

 

The offset does not directly change with diameter, the issue with diameter would be with tire size and overall diameter. Offset will be affected by width of the rim, i.e. 8.5 vs 10 inch rims. You should be fine with 20 x 8.5 as long as the overall diameter of the tire is close. Discount tire site has a calculator you can use.

 

Thanks!