G-xx : I think you/me/we should manage to the same OD for our spare vis-a-vis the tires on the 4 corners of our Avs, such that if those of us with 16" spare rims (that is all of us) with 17" rims on our rigs (the Z71/Z66 and select others) look at the spare tire size and it does not give us the same OD as we are running on the rig (that is my question for the true Z71/Z66 owners, I am not one so I cannot tell if GM manages to this result with a different spare tire size) then we can get the correct size on there.
and you are right, for those of us who have gone way beyond what our Avs came with (me, the Firestone Wilderness LE, if I recall, 265/70R16s - OD of 30.6 - were replaced with 275/70R17 Goodyear MT/Rs - OD of 32.4) and even assuming GM had matched our oem OD with the same OD on the spare, we are now out of whack. To be wise, I would need to get a 16" tire with a 32.5 (roughly) OD. From a quick look, the Dunlop Radial Rover RV 255/85R16 might be close for me, with an OD of 32.7 and a manageable section width. Plus it aint as expensive as my MT/Rs. Just a thought. I also have no idea if there is a fitment issue up in the spare tire area.