A couple weeks ago I posted a question about gearing and didnt get too many answers. I believe the stock gearing is 15/56 (I might be wrong on the front). Anyhow our bike is raced in the girls class and too a lesser degree in supermini. I was having problems getting my daughter adjusted to the 4stroke as she was riding it like her kx100 and ringing the heck out of it and constantly on the rev limiter. I figured gearing it higher for her might help. I figured with how my son and daughter were running it and testing it on our turn track, that a 54 rear would do the trick as they were running out of gears on a medium to long straight but just barely. I figured on a longer mx track they definitely would need taller gearing. Against my judgement I went with a 52 rear which my wife thought appropriate and although she is not on the rev limiter, the gearing is just a little too tall in the corners and doesnt come up on rev quickly enough. Anyhow my conclusion is that a 54 rear for most mx applications is probably the right gearing. My 200 pound rear still likes the stock gearing. Hope this helps someone as it seemed there was more info for gearing on bikes that were adult riden and for trail riding.