I can't fit a matching spare under there either, due to the Helwig sway bar that barely allows for the stock size to fit, even then I had to air it down. I used to have my dad's GMC truck and the spare was mounted on the front of the truck, in front of the grill. I thought about that if I get a set of 5 matching tires, but the weight factor kills it, already have a winch and bumper up there and taxing the front anymore with my slide in camper is just asking for trouble. My plan was to carry a power tank Co2 and some tire plugs, and hope I never have to use the mis match sized factory donut, but I leave it in place just in case. I like to get 5 tires and rotate the spare in whenever I can, two of six of my vehicles I can do this, I wish I could with my Cummins.