do not buy any adapter
I have a 33x12.50R15 MT on my spare
here is what you do
go to the hardware store
Get you some 1" spacers.. the ones i picked up were Brass and hallow throughout.. Get you some longer bolts... some washers..and some nuts..
take off the 3rd brake light bracket... insert the spacers...put in the bolts and wa-la.. your brake light is now higher and your tire will fit like a glove :}
just did mine the other day
here is a write up