and have found that the Sky wheels are a 5X110 with a 55mm offset.
So will I have to have spacers on these like on the Solstice ones?
Or is the 55mm too much of a difference from stock? What is stock...42?

 

What exactly does the offset mean when it comes down to wheels.

 

SS offset is 42mm on the 18" wheel. GM warranty on suspension would be trouble. Turns could cause problems too.

 

Offset is the distance between the centerline of the wheel and the hub mounting face.

This distance dictates the wheel’s placement within the wheel well. Offsets are described in three different ways, Positive, Zero and Negative.

Positive Offset: Hub mounting face is on the outside (towards the wheel face) of the wheel centerline.

Zero Offset: Hub mounting face is the wheel centerline.

Negative Offset: Hub mounting face is on the inside of the wheel centerline.

 

The Sky and the Solstice wheels are the same size 18x8 with a 55 mm offset. With a 225 45 18 you may need small 7mm spacers for the front.