I bought a clean used 03 RM65 for my 9-yr old son after he outgrew his PW80. I am a little scared of this bike (and he is too) since it is so quick and don't want him to get hurt or be afraid of riding. Can I reduce some of the quickness of this bike by changing to a smaller rear sprocket? I think the stock sprocket is 47 tooth, if anyone thinks this would help, what size should I go to?