Im picking up an 87' DR125 for my son. I dont know what the sprockets are now, but one is chipped. Since im going to replace them anyway, Can anyone tell me a good set up to use? I dont know the stock sizes(yet) but we will be strictly off road. Mostly trails, maybe a little track ridding too. Most of the time we will be less than 30mph and will almost never go over 50. He likes to pull a few wheelies too. Just looking to get a little more low end. Oh, and will the chain have to be changed out too? any help?