I am not 100% on the fitment of the pontiac G8 wheel. I would check the offset and bolt pattern first. If it is anthing like the 2010 camaro steel wheel. you will need to do 1 of 2 things.
1) open up the hub hole in the wheel to fit SyTy. and use an adapter in the rear.
Or
2) use a spacer in the front and an adapter in the rear.
The size of the spacer and adapter depend on the wheel offset.