Downside of BFG KO2 tires is their weight, which is substantially higher than other tires of equal diameter.
OEM Bridgestone Dueler H/L 400 (225/55 R18): 25 lbs
Compared to other 18's:
Yokohama Geolandar A/T G015 (235/60 R18): 34 lbs (+9 lbs, 36% heavier)
General Grabber AT2 (255/55/ R18): 34.5 lbs (+9.5 lbs, 36% heavier)
Toyo Open Country A/T II (255/55 R18): 35 lbs (+10 lbs, 40% heavier)
Nitto Terra Grappler G2 (255/55 R18): 35 lbs (+10 lbs, 40% heavier)
BF Goodrich All Terrain T/A KO2 (255/55 R18): 44 lbs (+19 lbs, 76% heavier) - This is 9 lbs heavier than the other 255/55s or 25% more than the same sized tires!
Also to compare the common 17's:
Yokohama Geolandar A/T G015 (225/65 R17): 29.8 lbs (+4.8 lbs, 19% heavier)
Toyo Open Country A/T II (235/65 R17): 32 lbs (+7 lbs, 28% heavier)
Hankook Dynapro ATM RF10 (235/65 R17): 32 lbs (+7 lbs, 28% heavier)
Cooper Discoverer A/T3 (235/65 R17): 34 lbs (+9 lbs, 36% heavier)
Kumho Road Venture A/T51 (235/65 R17): 34.3 lbs (+9.3 lbs, 37% heavier)
BF Goodrich All Terrain T/A K02 (225/65 R17): 39 lbs (+14 lbs, 56% heavier)
The KO2's are the heaviest of each size group. This is due to the thicker sidewalls, and meatier tread blocks I assume.
Keep in mind, these sizes are a little mixed, and some, especially the 255/55 R18's, are unlikely to fit without rubbing or modifications. Most of these tires are in the 35 lbs range, and adding un-sprung weight and rolling mass are typically detrimental to the performance of a car. Here, the trade off is off-road capability.