The wheels in offroad are bigger - so more torque on acceleration is on wheel.
The tungsten nitrid ones are more cutting the diff rings and so its more grippy - that i was told from Hupo Honigl 2 years ago. Top drivers dont use them in offroad.
On ISTC scale racing the wheels are smaller, so you want to long maintance intervalls so they choose the silicium nitrid (ceramic)
Hope I helped a lot.
