to determine how much cc's you need or if liquid cooled vs fan cooled. 1st how fast do want to go. 2nd groomed trail ridding, lake, off trail or deep snow. if you are going slow get a fan cooled machine. you will not foul out as many plugs as a liquid cooled going slow. if you are doing groomed trail ridding any above 440 will suit you fine, if you need speed a 600 gives good power, gas mileage and handling. off trial, deep snow , 2 track and seasonal roads go with 800cc and big lugs on the track. lake racing go with 1000 or bigger.