Stock M1009 tires are 31x10.50-15 (or R15 for the purists when referring to a radial).
Unmodified, you can run up to 33x12.50 if your springs don't sag too much. Over that size requires some modification (lift and/or fender trim).
My personal experience with that size aggressive tread tires (BF Goodrich Mud Terrain KM2) was that every other lug, the wider ones, rubbed on about 1/8" of the inner rear portion of the right front fender during the right conditions in a turn. I trimmed a bit of fender lip off with a Dremel, no more rub. I think a slightly less knobby tread would not have rubbed.
With the 12.50s my speedometer reads
approximately 1mph low at 25, 2 mph low at 35, 3mph low at 45, 4mph low at 65-75. (GPS measured, rounded off).
For those who will now jump in about tire sizes for M1008s, etc., he did ask specifically about M1009s.
Cheers