My Dad is new to snowmobiling and bought a Rev last year, we put 144 studs in it, but I forgot to change out the carbides. He has the precision skis and didn't have enough bite last year, he really has his heart set on the shaper bars, and I know that we have to go longer. When I look at Study Boy or Woody's websites they recommend either 6" for 144 studs or 8" for 168 studs. Does that mean 6" both inside and out? I searched for some other posts about this and wasn't quite sure what to make of it. I hear of people putting 6" on the outside and 4" on the inside, but if all the weight is on the inside carbide in a corner, wouldn't it make sense to have the longer carbide there? My other question is would it be worth it to go to the 8"? I don't think he would mind if it pushed at all, just so long as it would bite. If anyone could let me know what they've tried and what they recommend, I would really appreciate it. I know from experience that you guys will help alot.