I've got a 12 tooth front sprocket on and whatever the stock rear size is (44ish?). I don't have much room between the skid plate and rear sprocket. Options that I can think of in my current preference order:

1) Find a 10 or 11 tooth front sprocket.
2) Get a larger rear sprocket (3-4 teeth = 1 on the front?) and use washers to drop the skid plate if necessary.
3) I'm thinking about buying different tires (the ones with all the X's for tread) to replace the stock ones. Should I get them a touch smaller? That would obviously drop my clearance a bit. How much of a difference could that make?

What do you guys suggest?

 

Front sprockets make about 4-5 mph difference per tooth, rears make about 2 mph difference per tooth. Changing the front sprocket would be the best way to go, especially if you have limited clearance in the rear. If you still have the original chain and sprockets you should replace them all at once, mixing a new sprocket with an old chain or vice versa will cause excessive wear for both pieces.

20" rear tires are a good all-around size, and a 20" flat profile tire like holeshots or razrs will actually be a little shorter than the stock ones because the stock ones bulge out around the middle.