not really sure what the original size they put on back in 2007 but all the guys here change them from the carlisle's to the maxis.
I'll be visiting a friend tomorrow and I ll just read the dimensions on his tire, to post back here.
Additionally, I've read the reviews on the bighorn vs bighorn 2.0 and since I'm pretty happy with bighorn I think I stick with those. But I got a few months of rubber left on mine.
for the rears i see this spec 26x10x12
M918 Bighorn Radial Rear
M917 Bighorn Radial Front
for the fronts it looks like a 26x9x12 but as I said , i ll check with my friend tomorrow