According to what I have read from books and internet, it is said that for different mud, there are different optimized tire width.
But here in Southwest Florida, the Mud we experience is mostly pretty thick, so most jeepers here are using wide tire, usually 12.5 inch. But 13 or 14 inch widht is also quite common.
Some jeepers told me they will use super wide tire so they can float on the mud and jsut spin the tire to throw the mud backward to gain forward momentum. I am not sure if it is true or not yet. But I do see those
guys doing that on Mud for fun.