Has anyone put a full-size spare underneath? If so, what additional parts were need if this is at all possible. Thx.

I'm running 255s all around, and tried to mount one of 255s underneath. Unforetunely, it doesn't fit. So I'm stuck with the limited spare. But you think about it, how many times are you going to use that spare? It'll probably rought off the rim before you get the full life of it.

Great point. I have some 18" OEM rims just sitting in the garage and started to ponder the idea.

When I put my trailer hitch on my N* SRX, the spare barely fit as is (if I remember right, the mufflers were right there because there definitely was heat shielding I bent up).

I personally don't see much need for a spare. I've had 1 flat tire in my 16 years of driving and it was my fault (I tried to drive on a low tire to get home instead of filling it up right away and the sidewall tore). I don't know if you still have onstar or how many miles you have on yours, but you probably have free road side assistance. I get free roadside assistance from Sam's Club. I took the spare out of my CTS since I can just hit the onstar button and someone is there in 30 minutes. Plus, my wife drives the SRX, so if she gets a flat, she will probably call me or Sam's to send someone to fix it. That's just my 2 cents though.

I hit something on the road in June and ruined a rear tire...had to drive 155 miles on the temp spare to find a tire the right size for the rear in Iowa......the stupid "spare Kit" that comes on the 2010's would not have helped at all as the size wall blew out; and 155 miles seems like eternity at 60 MPH!!