i have seen it done for slalom, i can see it being useful for DH but not for freeriding really, normally you go wide back narrow front so you can have some more stability in the back and a tighter turn from the front
I was looking at running 195's on the front with otang 4pres with the 180's at the back with Krypto classics....i was thinking that the 4pres and wider would grip better, and the 180s would slide more???