Just get the one for a 31" it will fit the smaller stock tire.
I bought one for the stock tire off ebay, it ended up fitting on the 245/75R15 (30.6") I added later, just a little tight.
I don't have a tire cover anymore, it froze on the first winter, destroyed it trying to get it off. Decided it looked better without a tire cover anyway.
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2005 CRD "
Ol' Blue"
Red Ryder carbine-action, two hundred shot range model air rifle with a compass in the stock and this thing which tells time.
My build page- RL Komodo Rear and TJM Front Bumper, armored, lifted, JBA Steel D30, 4.10s and ARB air lockers.